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Design of Differential LNA and Double Balanced Mixer using 180 nm CMOS Technology
Microprocessors and Microsystems 71 (2019) 102850
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Design of Differential LNA and Double Balanced Mixer using 180 nm CMOS Technology C. Kalamani Department of ECE, Dr. Mahalingam College of Engineering and Technology, Pollachi, Coimbatore, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 13 May 2019 Revised 15 July 2019 Accepted 24 July 2019 Available online 25 July 2019 Keywords: Radio frequency MOSFETs LNA CMOS Source mixer Double balanced mixer
a b s t r a c t The RFICs plays an important role in wireless communication systems due to their effective operation in the 2.4 GHz frequency, popularly known as ISM (Industrial, Scientific and Medical) band. LNA and Mixers are the major components used in transceivers for the purpose of amplification and frequency translation. Such LNAs and mixers are of different kinds and various techniques are used for their optimization. The paper describes the design of a differential LNA with two single stranded source degenerate LNAs with greater increase in gain. differential LNA is combined with Double balanced mixer with a current mirror circuit and BALUN with the bias controlling MOSFETs are used to show the better performance at 2.4 GHz frequency range. CMOS has become a viable technology for the design of high-performance receivers in the Radio Frequency (RF) regime. The conversion gain of 22.28 dB and IF of 595 MHz of Differential LNA with Double Balanced mixer are higher than the cross comparison results of the other methods at 180 nm technology. CMOS implementation of the design is done using the Cadence Virtuoso tool of 180 nm technology at 2.4 GHz frequency and 1.8 V of supply voltage. © 2019 Published by Elsevier B.V.
1. Introduction With the continuous and rapid development of microelectronic devices like the mobile phone, laptop, radio, wireless network and GPS (Global Positioning System), a diversity of electronic devices are extensively used in day-to-day life. Meanwhile, new commercial, useful and cultivated extraordinary performances are required for electric devices. With investigation and advancement of CMOS technology, it influences a low cost, miniature size and low voltage integrated circuit capable to incorporate entire structure on single chip. The trials are endless and designate caution in deliberation of RF Designs [1–3]. In Mixer in source circuitry is used to combine the Low frequency message signal with the locally generated signal to produce high frequency signal [4,5]. In the microelectronics applications, RF Integrated Circuits (RFICs) plays an improtant role due to the lower cost and less power operation in the 2.4 GHz frequency range. RF front end design contains Low Noise Amplifier (LNA), Mixer and Voltage Controlled Oscillator (VCO), and Power Amplifier (PA). Mixers, and LNAs are important blocks in transceivers. The output of mixer consists of sum and difference of input signal and Local Oscillator (LO) frequency. The block diagram depicts a simplified diagram of a base station transceiver in Fig. 1.
E-mail address: [email protected] https://doi.org/10.1016/j.micpro.2019.102850 0141-9331/© 2019 Published by Elsevier B.V.
This system contains receiver and a transmitter sections. In the receiver section, the signal would enter into the antenna. The signal usually becomes weak due to noise interference and attenuation at the antenna, and it needs to be properly arranged to enter the system. The LNA will amplify the desired signal while adding as little distortion as possible. Then the signal is sent to the down conversion mixer and low pass filter (LPF) which should be converted and tuned. The analog signal is then converted to digital data via the analog-to-digital converter (ADC). Finally, the bits of data are used for processing purposes. In the transmission section, the bits of data are converted from digital bits to analog signal by the digital-to-analog converter (DAC). The signal is then sent to up conversion mixer and high pass filter (HPF), which shifts the original frequency to a higher frequency for communication. The new signal is then sent to a power amplifier (PA) to increase the power for the signal, and prepare the signal for its distance travel. The signal is then transmitted though the antenna. LNA plays a key role in the receiver. It receives very low power from the antenna and amplifies them along with the decrease in the noise to a greater level. The demand of LNA rises due to the progress of the modern technologies such as GPS, Bluetooth, cell phones etc., Mostly in wireless communication system, the LNA is critical to design because it provides adequate gain from the little signal power which is established by the antenna, not only to make signal to noise ratio degradation but also to sustain signals with low power dissipation.
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Fig. 1. General RF transceiver block diagram.
Fig. 3. Basic single balanced mixer.
Fig. 2. Typical gain compression characteristic for a non-linear amplifier/mixer.
The performance of the LNA is mainly affected by three parameters namely the input impedance, gain and noise figure of the amplifier. The reduction of power consumption of radio frequency front end is the most important one in wireless communications. The basic structure of a single mixer is that it has two input port and one output port. It combines the carrier signal, either RF or intermediate frequency (IF) subject to up conversion or down conversion, with input from the local oscillator (LO).The properties of mixer are nonlinearity and time-variance. The operation is accomplished in time domain by multiplying two input signals:
x(t ) = A cos ω1 t
(1)
y(t ) = B cos ω2 t
(2)
Mixer output is
x(t ).y(t ) = A cos ω1 t.B cos ω2 t AB AB = cos(ω1 − ω2 )t + cos(ω1 + ω2 )t 2 2
(3)
The mixer output contains nonlinear components, which introduce more noise, and improper design may also cause leakage effects, which complicate the system design. The nonlinear characteristic of mixer is that if exceeding a certain input level causing a gain compression as shown in Fig. 2. Beyond this point the intermediate frequency fails to track the RF power at 1 dB upsurge in RF power will effect in a 1 dB upsurge in the close to IF power. There is a compromise between designing of mixer and LNA in rapports of the gain, noise figure, and power feeding. Single Balanced Gilbert cell mixer design operates is depicted in Fig. 3. The single wave RF signal first enters into the base of the transistor M1, while the LO signal is parted into the base transistors M2 and M3. The input RF signal is then transformed into current. The current signal is combined with the switching LO signals in M2 & M3. The resultant current is converted back into voltage
via the load resistors R1 & R2, then the output exits from the respective IF outputs. The ideal SB Gilbert cell appears to be very beneficial. This design contributes moderate good gain at a lower LO power and low power consumption; occasionally this specification can be compromised for further desired specifications. When a designer needs a higher gain and/or system linearity and it tends to tradeoff power consumption or even NF achieve that designs goal. It is illustrated that this design is not adequate powerful to encounter all the many mixer design specifications claimed by the communication industry. Even though the SB Gilbert cell mixer is a solid design and achieve the goals for some design systems, it may not be satisfactory for designs that call for increased mixer specifications. This is the place where the Double Balanced (DB) Gilbert cell mixer can meet those requirements. The most normally used active mixer architecture consists of DB Gilbert cell mixer, and comprises advances over other designs comprising the SB Gilbert cell mixer. The DB mixer can accomplish greater mixer provisions at the cost of a slight surge in NF and overall design power consumption. The normally doublebalanced mixer with Gilbert Cell is used in RFIC designs. Gilbert cell mixers are broadly used due to their practical conversion gain, linearity, isolation and noise figure. To expand the linearity of the mixer, many techniques and structures have been innovated. Use of these techniques has resulted in complex circuit with high power consumption, more noise, and higher cost. Simple LNA designs do not provide better noise performance. The proposed method is planned to design a mixer and LNA to attain extraordinary gain, little noise figure and reduced power consumption in 0.18 μm CMOS technology using Cadence Virtuoso tool. The proposed mixer circuit operates at a supply voltage of 1.8 V. The organizations of the paper are Section 2 describes existing methods, Section 3 explains the proposed designs, and Section 4 describes the results and discussion. Finally Section 5 concludes. 2. Existing methods The existing methods of LNA and mixer design approaches have been proposed in the past. All the approaches have its specific advantages and disadvantages. Several popular approaches are MultiTanh, current bleeding, Switched bias, Folded cascade, Bulk driven method, CCPD, MGTR for mixer design and Source degenerate LNA design for Low Noise Amplifier.
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Fig. 5. RF circuit with source degeneration. Fig. 4. Source degenerate LNA.
2.1. Source degenerate LNA The design of LNA involves compromise among gain, linearity, Noise Figure (NF) and power consumption. The design optimization technique is used to get tradeoff between gain and linearity. Different topologies of LNA are available. The source degenerated LNA is shown in the Fig. 4, inductance L1 which is at drain of M2 along with node capacitance vibrate at the operational frequency and offer M3 and it is also in current mirror linking with M1 and their ratio will govern the current through the cascade subdivision. The voltage across gate source of M1 is determined by the proper selection of width of M1. The value of the resistance R should be superior to the output impedance of prior juncture. The infinite input impedance is provided to the cascade by M1. The advantage of cascade is explained that it is bright to diminish the effect of gate to drain capacitance i.e., miller capacitance since the input resistance of M2 is considerably lesser than the output resistance of M1. By using power constraint noise optimization technique, the width of M1 is obtained. The parameters Lg and Ls, which are used for input impedance matching, are obtained by using equivalent small signal model. The mixer is described through its vigorous design parameter which consists of conversion gain, linearity, noise figure, and port isolation as [1–11]. The active mixer leads to a superior conversion gain and little noise figure with poorer the linearity and power consumption [12–16]. The RF input circuit of the mixer has been revised with auxiliary basis disintegration for enlightening the linearity of the double balance Gilbert cell mixer. Source degeneration circuit for mixer is shown in Fig. 5. In LNA, the resistances are comprehended as inductors Ls. The source resistor Rs prominently enriched the linearity of the mixer. But, resistor will produce a root for voltage drop and later a desired surge in the voltage barriers to confirm the devices endured in saturation. Additional crucial tricky using a resistor is producing the noise. The resolution is applied to use an inductor. There are numerals of concerns when using an inductor Ls, 1. The circuit will be extra frequency dependent. 2. Also the uses of inductors in CMOS incline to require low Quality (Q) factors – typically 2–3. 3. Source inductor will have a major consequence on the input impedance (Re) and necessity will be tested to safeguard the impedance is positive.
The CMOS down Conversion Gilbert mixer for wireless communication has been optimized to consume less power which is described as [17,18]. The Gilbert mixer cell topology is frequently employed for assembling active mixer [19–23]. The Gilbert cell is widely used because it provides extraordinary conversion gain, noble port-to-port isolation and small even-order distortion as [24]. A low power transceiver for Wireless Sensor Networks (WSN) is designed using a receiver, a fractional-N frequency synthesizer, and a class-E transmitter, and it is superior with output parameter such as sensitivity, power consumption, and silicon area which are described as [25]. The CMOS receiver architecture is combination of LNA and Mixer. The proposed architecture operates at 2.4 GHz RF frequency. An unconditionally stable Low Noise Amplifier for the L1 carrier of Global Positioning System (GPS) is working on the 1.57542 GHz band as [26]. Gilbert cell mixer proposal and action are described in [27]. CMOS receiver architecture with combined LNA and Mixer is presented as [28]. LNA and Mixer are designed using Cadence virtuoso tool at 180 nm technology. Differential LNA and Gilbert Mixer are also designed in order to achieve greater gain and small noise figure along with better conversion gain. The design of up-conversion mixer using the current mirror and current-bleeding with a simple degeneration resistor is presented as [29]. 3. Proposed method The proposed method describes the design of differential LNA, Single balanced mixer using current mirror along with BALUN and double balanced Gilbert cell mixer design using the BALUN along with the biasing and controlling MOSFETs, integrated design of differential LNA and double balanced Gilbert mixer. The motivation to design differential LNA is provided that it offers a stable reference point and noise reduction. Two single ended circuits are used to design one differential circuit. It uses the cascade design whereas the advantage of cascade has the ability to diminish the effect of gate to drain capacitance i.e., miller capacitance since the input resistance is much lesser than the output resistance. Gilbert mixer has numerous significant features that it is, sufficient conversion gain with suitable load. A better port-to-port isolation and little noise figure is obtained by double-Balanced Gilbert cell topology. It uses mechanism on the idea of trans linear structure. The shortcomings of this mixer have restricted linearity and frequency, which will be contingent on identical. The input transistors of these mixers should be in saturation region.
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3.1. Proposed method of differential LNA
From the circuit designed for plotting the DC response curve, gm value is found as,
The proposed method of differential LNA has been designed from two single ended source degenerated LNAs. It uses the cascade design whereas the benefit of cascade is enlisted that it is able to reduce the effect of gate to drain capacitance meanwhile the input resistance of M2 is much smaller than the output resistance of M1. The differential LNA has several important advantages when compared to single ended circuits. The key benefit of using differential LNA is described that it offers a steady reference point. The measured values of this LNA are constantly taken with respect to former half circuit. The foremost benefit of using this LNA over other topologies is noise reduction. Two single ended circuits are needed in order to create one differential circuit in which each transistor and circuit has complementary transistor.The positive voltage is given to the gate of first single ended circuit while negative voltage is given to the gate of second single ended circuit or else grounded. The use of source degeneration is to generate gate current noise and the total noise is toughly decrease by using a capacitance in shunt with the amplifying MOS transistor of the LNA. It upshots precise low noise figure and very low power consumption. So the differential LNA is chosen for receiver design. The positive-feedback loop is applied by adding couple capacitors between the drain and source of the output transistors and their value should be selected compromise with the gain and stability. The feedback capacitors can raise the chip size, but the gain can be improved at an ample greater rate than size. While choosing the input transistor’s size, a key design compromises the current concentration essential for least noise figure. The optimal width of the input transistors is selected to get best noise performance. 3.2. LNA specifications The LNA specifications of RF frequency (Input) = 2.4 GHz, noise figure <5 dB, gain >10 dB, supply voltage = 1.8 V are designed and simulated. 3.3. Mixer specifications RF frequency = 2.4 GHz, local oscillator (LO) frequency = 2.9 GHz intermediate frequency (IF) = 500 MHz, gain > 10 dB, noise figure <5 dB. 3.3.1. Design procedure for LNA The width of the M1 transistor can be found by,
1 W= 3.Cox.ω.Rs.L
(4)
∈ox 3.45 × 10−11 = = 8.42 × 10−3 F/m2 tox 4.1 × 10−9
(5)
where ɛox =ɛo . ɛr , hence the width of the transistor is,
3 × 8.42 × 10−3 × 2π × 2.4 × 109 × 50 × 180 × 10−9 = 291.7 μm The gate-source capacitance is calculated as given below.
Cgs =
2 × w × Cox × L 3
2 × 2.917 × 10−4 × 8.42 × 10−2 × 180 × 10−9 3 = 2.947 × 10−13
Cgs =
Substituting the values of gm and Cgs , Ls = 108.5 fH
f =
2π
1
(7)
(Ls + Lg ) × Cgs
The above equation can be rearranged to form the following equation,
1 = 14.92 nH Cgs × w2
Lg =
(8)
3.3.2. Design procedure for mixer The procedure involved in designing a mixer is furnished below, With voltage gain of 6 dB we can calculate gm, Conversion Gain
C.G =
2
π
RL Rs +
(9)
1 gm
Convert dB to conversion gain = 106/10 = 3.98
gm =
2
π
.
RL − RS Vgain
−1
(10)
Let RL = 500 , RS = 10 , gm = 0.01429 gm calculated and obtain W by assuming the minimum gate length to be 0.180 μm and a current of 2 mA,
w=
gm 2 .L 0.014292 × 0.180 = = 105 μm 2.k p .IDS 2 × 171 × 10−6 × 2 × 10−2
(11)
where k p = μ0 .Cox For the current mirror circuit the width of the transistor is 10 μm. 3.3.3. Design procedure for LPF Low pass filter with cut-off frequency of 500 MHz, the L and C values are calculated as follows,
Z0
L=
π × λc
=
500
π × 500 MHz
= 310 nH
(12)
where Z0 is characteristics impedance and λc is cutoff frequency
C=
1 1 = = 1270 fF Z0 × π × λc 500 × π × 500 M
(13)
The mixer has converts RF input voltage into current. The resultant current is then multiplied by the LO signal at the mixer. If the drive voltage at the LO port is large, the RF current will be efficiently multiplied with 50% duty cycle in which its frequency is that of the local oscillator. However the single-balanced mixer has port isolations and the conversion gain can be simply attuned and established on the gm and ZL. It has some drawbacks. 1. Signal density at output 2. RF unstable owed low noise immunity
1
w=
gm × Ls = 50 Cgs
3.4. Proposed method of single balanced Gilbert cell mixer
where Cox = Capacitance of the gate-oxide, Rs = Source resistance, L = length of the device, ω = angular frequency. The gate-oxide capacitance is found as follows,
Cox =
gm = 135.86 m,
(6)
These drawbacks are overcome by using current mirror and Balun circuit with existing mixer circuit as below. A current mirror circuit is used to copy a current through one active device by controlling the current in another active device of a circuit, keeping the output current constant irrespective of loading. An idyllic current mirror is merely a model of inverting current amplifier that reverses direction of the current. The current mirror is employed to give bias currents and active loads to circuits. It can model a more faithful current source. There are three key specifications of a current mirror are.
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1. The transfer ratio. 2. AC output resistance to define magnitude of the output current with the voltage applied. 3. The smallest voltage drops across the output of the mirror essential to create it work appropriately. A Current Mirror topology is present in the driver stage due to its non-linearity as well as the linearity of conventional Gilbert cell mixer is not worthy linear. Since current mirror topology is highly linear, it is used to produce much better linearity. A BALUN is an electrical device that alters between a balanced signal and an unbalanced signal. Transformer baluns can also be employed to join lines of contradictory impedance. Occasionally, in the case of transformer baluns, magnetic coupling is used but not necessities do it. Common-mode chokes are also used as baluns and work by eradicating, rather than overlooking, common mode signals. This mixer is suffered from IF leakage and second order effects. 3.5. Proposed method of double balanced Gilbert cell mixer Double Balanced Mixers are used to avoid the issues of single balanced mixer. It achieves high CG, linearity, and port isolation at the cost of a slight increase in NF and power consumption. DB Gilbert mixer is mainly a combination of two SB mixers and it is connected in antiparallel for LO and parallel for IF with source degeneration to get linearity and stability of the mixer. The LO terms sum to zero in the output; however the converted IF signal is doubled in the output. This mixer so offers a high degree of LO-IF isolation, drop of noise in the outputs, aiding filtering necessity at the output. Differential RF input in the transconductance part and switching operations consist of four transistors. Thus switching operation converts current into voltage. Balun is used to deliver single ended inputs and outputs and will thus combine the differential IF signals to provide a 3 dB rise in the differential conversion gain. Gates of the RF MOSFETS 1 & 6 are grounded via 10 K resistors that block any RF signal and to guarantee correct bias, the tail MOSFET 9 is connected to a negative supply. The tail current is set by the ‘bias’ variable. The DB mixer has better transconductance, thus it has higher CG. DB Gilbert cell has the control over the harmonic products to produce linearity. By adjusting the transistor stacking and setup is done for maintain port isolation. The number of transistor increases and improper switching of transistor leads to rise in NF and these transistors needs more supply. This increases the power consumption of DB mixer.
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means of a bond-wire. LG = 14.92 nm which is higher than L which is integrated inductor. The key improvement of this circuit is low area, due to the less number of components. The circuit has only two inductors. 4. Results and discussion The single balanced Gilbert cell mixer, double balanced Gilbert cell mixer, source degenerate LNA and differential LNA have been designed using Cadence Spectre_RF tool on TSMC 180 nm technology. Cadence EDA tools are used Virtuoso 64 for Schematic Editing and Spectre for Simulation. The Fig. 6 shows the schematic diagram of the source degenerate LNA with the input frequency of 2.4 GHz. The source degenerate LNA is used to design differential LNA which increases the linearity and stability. For the Source degenerate LNA, Gain and Noise Figure are obtain from s-parameter analysis and shown in the Fig. 7a and b respectively and about 10.8507 dB of Gain and ∼1 dB of Noise Figure with 179.8E−3 W at 2.4 GHz frequency. The Fig. 8a shows the schematic diagram of proposed differential LNA. Two single ended Source Degenerate LNAs are used to design a differential LNA with calculated values. From transient
Fig. 6. Schematic of source degenerate LNA.
3.6. Combined differential LNA and double balanced Gilbert cell mixer The low voltage and low power RFIC are implemented. It should accomplish low power dissipation in the front end of receiver. The detached blocks entail two translations, one from current to voltage at the LNA output, and the other from voltage to current at the mixer input. The multiple DC current paths in circuit are a major source of power consumption and it should be reduced by integrating the proper current-mirror design. The low noise amplifier LNA has a single ended topology which is followed by the double balanced mixer. The current mirror circuit and balun are used for integrating LNA and mixer. DB mixer is no port isolation at RF and IF port, so it does need complicated filters. It is also free from self-mixing of RF and LO signal. A low-pass filter is designed with cut off frequency of 500 MHz which has calculated value of L = 310 nm and capacitor C = 1270 fF is used to allow the desired frequency and other harmonics are attenuated. L requires typically a low value and can be realized by
Fig. 7. (a) Gain of source degenerate LNA. (b) Noise figure of source degenerate LNA.
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C. Kalamani / Microprocessors and Microsystems 71 (2019) 102850
Fig. 9. (a) Gains of differential LNA. (b) Noise figure of differential LNA. Fig. 8. (a) Schematic of differential LNA. (b) Output of differential LNA.
response of LNA, it shows that the output voltage (green) which is amplified version of input voltage (Red) as in Fig. 8b. Fig. 9a shows the gain plot of the differential LNA and it is measured as 20.2852 dB at 1.8 V with 2.4 GHz by adjusting transistor size, passive components of the design. The noise figure of the differential LNA is obtained using scattering parameters. The graph in Fig. 9b shows that the LNA has a noise figure of 2.14547 dB at 1.8 V supply voltage, 2.4 GHz operating frequency. Since noise figure meets the specification. 4.1. Mixer results Fig. 10 shows the schematic diagram of the single balanced Gilbert cell mixer using the current mirror circuit and BALUN and its output. The transient response plot consists of the input RF = 2.4 GHz and LO frequencies = 3 GHz and the output IF frequency signals = 2.9 GHz with power = 206.2 nW. The IF signal is distorted, thus guided through a low pass filter. The final output through the filter is distortion less. The differential signal at LO, RF and IF are low. To boost these signal, A double balanced Gilbert mixer is designed and the results obtained at RF frequency are 2.4 GHz; LO frequency: 3 GHz; IF frequency: 6 GHz with power 140.4 nW, which are shown in Fig. 11. Double balanced mixer, both of differential transistors should be driven by the RF signal. The differential signal v1 and v2 are measured at LO, RF and IF are higher than the SB mixer results. The performance of DB mixer is higher than SB mixer. Source degenerate LNA is integrated with the double balanced Gilbert cell mixer to reduce the conversion losses and power dissipation due to DC sources. The designed LNA is single ended topology. So a balun
Fig. 10. (a) Schematic of single balanced Gilbert cell mixer. (b) Output schematic of single balanced Gilbert cell mixer.
C. Kalamani / Microprocessors and Microsystems 71 (2019) 102850
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Fig. 11. (a) Schematic of double balanced Gilbert cell mixer. (b) Output of double balanced Gilbert cell mixer.
Fig. 13. (a) Schematic of differential LNA integrated with double balanced Gilbert cell mixer. (b) Output of differential LNA integrated with double balanced Gilbert cell mixer.
is used to transfer the single ended signal to a differential signal. The degradation of balun can be compensated by current mirror. Current mirror will boost the linearity of the circuit. Fig. 12 is the schematic of Source degenerate LNA which is integrated with the double balanced Gilbert cell mixer. RF input for LNA: 2.4 GHz; LO frequency input for mixer: 3 GHz; IF frequency: ∼6 MHz with power: 3.735 W. Output waveform is slightly distorted. This can be overcome by the integration of Differential LNA with the double balanced mixer and the Fig. 13 shows the schematic and the output with RF input for LNA: 2.4 GHz; LO frequency input for mixer: 3 GHz; IF frequency: ∼ 6 MHz with 3.747 W. The output of integration of Differential LNA with the double balanced mixer is distortion less. 5. Post-layout simulation results
Fig. 12. (a) Schematic of source degenerate LNA integrated with double balanced Gilbert cell mixer. (b) Output of source degenerate LNA integrated with double balanced Gilbert cell mixer.
The proposed LNA and mixer are designed by 180 nm technology, and simulated using Cadence SpectreRF simulator. Layout design of proposed differential LNA circuit is shown in Fig. 14a. Fig. 14b provides the output waveform for the proposed differential LNA. The layout has been drawn and the association of layers has been positioned as symmetrical as possible to drop mismatches. All of the components in this design, plus spiral inductors and metal-insulator-metal capacitors, are employed in on-chip. The parasitic resistances and capacitances are also removed from the layout and taken into account in simulation [27]. Fig. 15 shows the layout design and output respectively for the proposed double balanced Gilbert cell mixer. Table 1 illustrates the comparison between the source degenerate LNA and Differential LNA. From the table, it is observed that
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Fig. 14. (a) Layout design for proposed differential LNA. (b) Output of layout design of proposed differential LNA. Table 1 Comparisons of source degenerate and differential LNA. Parameters
Source degenerate LNA
Differential LNA
Noise figure Gain Power
2.14547 dB 10.8587 dB 179.8 mW
∼1 dB 20.2852 dB 167.1 mW Fig. 15. (a) Layout design for proposed double balanced mixer. (b) Output of layout design of proposed double balanced mixer.
the noise has been greatly reduced in the Differential LNA and the gain has been slightly increased with the increase in power consumption. Table 2 shows the comparison of the results obtained from the proposed methods of single and double balanced Gilbert cell mixers and the results obtained DB mixer is increase in IF frequency of 6 GHz with increase in power consumption. DB mixer is constructed using 2 SB mixers. Layout design and its output of both differential and double balanced mixer are obtained. The comparison of layout output waveform and simulated output waveform are almost equal. Integrated results of Source Degenerate LNA and DB Mixer are distorted transient response as compared that of Differential
LNA and DB Mixer. Differential LNA and DB Mixer with current mirror, bias circuit, filter and balun are integrated. The results of later is show noiseless transient response with almost same power. The cross comparison results are shown in Table 3. The conversion gain of 22.28 dB and IF frequency 595 MHz of Differential LNA with Double Balanced mixer are higher than the cross comparison results of the other methods at 180 nm technology. Table 3 shows the cross platform comparison of proposed mixer with existing. The results show that the proposed method outperforms compared with existing methods.
Table 2 Results obtained from the integration of LNA and mixer. Parameters
SB Gilbert cell mixer
DB Gilbert cell mixer
Source degenerate LNA + DB mixer
Differential LNA + DB mixer
RF (GHz) LO-frequency GHz IF frequency GHz Power
2.4 3 2.9 206.2 n W
2.4 3 6 140.4 μ W
2.4 3 0.588 3.735 W
2.4 3 0.595 3.747 W
Table 3 Cross platform comparative performance. Parameters
2
3
4
9
10
19
Differential LNA with DB mixer
Technology μm Power supply (V) IF freq (MHz) LO freq (GHz) RF freq (GHz) Conversion gain (dB)
0.18 1.2 100 1.8 1.9 5
0.13 1.2 10–400 1.8–2.6 1.810 1.1
0.18 1.8 1 2.419 2.42 16.2
0.18 1.8 100 5.1 5.2 6
0.18 1.8 100 5.1 5.2 6
90 nm 1.8 100 2.3 2.4 21.4
0.18 1.8 595 3 2.4 22.28
C. Kalamani / Microprocessors and Microsystems 71 (2019) 102850
6. Conclusions A single stranded source degenerate LNA, a differential LNA, a single and a double balanced Gilbert cell mixers are designed and simulated. From the results obtained, it is concluded that the Noise has been greatly reduced while using proposed method of Differential LNA along with little increase in gain and power consumption. Single balanced Gilbert cell mixers will not provide a desired output for all the frequency ranges. It is confined only to higher frequencies and it is not accurate for many lower frequencies. The linearity and gain are less for single balanced mixer. In order to overcome this, Double balanced Gilbert cell mixer is designed. Usually power consumption and noise will be higher in these double balanced structures although they provide high gain and linearity. Further, optimization will improve its performance. This will find its application in the RF frequency range, ISM band and many. Finally, the differential LNA and the double balanced mixer are integrated to provide the better performance. Declaration of Competing Interest We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. References [1] [2] [3] [4]
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[13] S.A.Z. Murad, R.K. Pokharel, M.A. Abdelghany, H. Kanaya, Yoshida, High linearity 5.2 GHz CMOS up-conversion mixer using super derivative superposition method, in: Proc. TENCON IEEE, 2010, pp. 1509–1512. [14] A. Saberkari, B. Shahriar, Shokouhi, A. Abrishamifar, A low voltage highly linear CMOS up-conversion mixer based on current conveyor, IEICE Electron. Express 6 (2009) 930–935. [15] G. Sapone, G. Palmisano, A 1.5 V 0.25 μm CMOS up converter for 3-5 GHz low power WPANs, Microw. Opt. Technol. Lett. 49 (9) (2007) 2209–2212. [16] S.H.-L. Tu, S.C.-H. Chen, A 5.26-GHz CMOS up-conversion mixer for IEEE 802.11a WLAN, in: Proc. of 4th IEEE International Conference on Circuits and Systems for Communications (ICCSC), 2008, pp. 820–823. [17] J.P. Silver, Gilbert Cell Mixer Design Tutorial, RF, RFIC and Microwave Theory Design, www.rfic.co.uk, pp: 1–20. [18] R.M. Ramzan, in: Gilbert Mixer Simulation (Cadence SpectreRF), Electrical Engineering Department (ISY), Linköping University, Sweden, 2007, pp. 1–26. vol. 03, issue 2. [19] V. Aparin, L.E. Larson, Modified derivative superposition method for linearizing FET low-noise amplifiers, IEEE Microw. Theory Tech. 53 (Feb. 2005) 571–581. [20] G. Mehdi, Highly Linear Mixer for On-chip RF Test in 130 nm CMOS Master thesis Division of Electronic Devices at Linköping Institute of Technology. [21] S. Gao, A high-linearity low-noise figure active mixer in 0.18 um CMOS, 5th International Conference on Wireless communication Networking and Mobile Computing, 09/2009, 2009. [22] V. Nath, http://www.ide.iitkgp.ernet.in/Pedagogy_view/example.jsp?USER_ID= 210. [23] M.K. Pandram, R.C. Gurjar, A low power down conversion CMOS gilbert mixer for wireless communications, Int. J. Eng. Res. Appl. 4 (7) (July 2014) 186–190 (version 1). [24] R. Sharma, A. Chaturvedi, M. Kumar, A comparative study of different types of mixer topologies, ICTACT J. Microelectron. 02 (1) (April 2016) 182–187. [25] D. Sharath Babu Rao, R.K. Sreelakshmi, Design of LNA and MIXER for CMOS receiver front ends, Int. J. Innov. Res. Technol. 04 (3) (2017) 97–102. [26] S.I. Rahman, S.A. Kareem, S. Habeeb, Design of a low noise amplifier using 0.18 μ;m CMOS technology, Int. J. Eng. Sci. (IJES) 4 (2015) 11–16. [27] A. Pandey, D. Prasad, V. Nath, A 3.65 mW, Amplifier-Based Up-Conversion Mixer for Zigbee Application, in: Proceeding of the Second International Conference on Microelectronics, Computing & Communication Systems (MCCS 2017), 2019, pp. 785–793. [28] R.K. Sreelakshmi, D. Sharath Babu Rao, Design of LNA and mixer for CMOS receiver front ends, Int. J. Innov. Res. Techno. 4 (3) (2017) 97–102. [29] Q. Wan, C. Wang, F. Yu, Design of a 2.4 GHz high-performance up-conversion mixer with current mirror topology, Radioengineering 21 (2) (June 2012) 752–757. C. Kalamani received her B.E. degree in Electronics and Communication Engineering from Government College of Technology, Coimbatore, India, in 20 0 0, M.Tech. in Advanced Communication Systems from SASTRA University, Tanjore, India, in 2002. She received her P.hD in Information and Communication Engineering from Anna University, Tamil nadu, India, in 2018. She is working as assistant professor, Dr. Mahalingam College of Engineering and Technology, Coimbatore. Her research interests include VLSI design, Digital Communication, Microwave and Optical Communication technique. She is a member in ISTE. She has 8 international/national journal and more 10 national and international conferences publications.
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Microprocessors and Microsystems journal homepage: www.elsevier.com/locate/micpro
Design of Differential LNA and Double Balanced Mixer using 180 nm CMOS Technology C. Kalamani Department of ECE, Dr. Mahalingam College of Engineering and Technology, Pollachi, Coimbatore, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 13 May 2019 Revised 15 July 2019 Accepted 24 July 2019 Available online 25 July 2019 Keywords: Radio frequency MOSFETs LNA CMOS Source mixer Double balanced mixer
a b s t r a c t The RFICs plays an important role in wireless communication systems due to their effective operation in the 2.4 GHz frequency, popularly known as ISM (Industrial, Scientific and Medical) band. LNA and Mixers are the major components used in transceivers for the purpose of amplification and frequency translation. Such LNAs and mixers are of different kinds and various techniques are used for their optimization. The paper describes the design of a differential LNA with two single stranded source degenerate LNAs with greater increase in gain. differential LNA is combined with Double balanced mixer with a current mirror circuit and BALUN with the bias controlling MOSFETs are used to show the better performance at 2.4 GHz frequency range. CMOS has become a viable technology for the design of high-performance receivers in the Radio Frequency (RF) regime. The conversion gain of 22.28 dB and IF of 595 MHz of Differential LNA with Double Balanced mixer are higher than the cross comparison results of the other methods at 180 nm technology. CMOS implementation of the design is done using the Cadence Virtuoso tool of 180 nm technology at 2.4 GHz frequency and 1.8 V of supply voltage. © 2019 Published by Elsevier B.V.
1. Introduction With the continuous and rapid development of microelectronic devices like the mobile phone, laptop, radio, wireless network and GPS (Global Positioning System), a diversity of electronic devices are extensively used in day-to-day life. Meanwhile, new commercial, useful and cultivated extraordinary performances are required for electric devices. With investigation and advancement of CMOS technology, it influences a low cost, miniature size and low voltage integrated circuit capable to incorporate entire structure on single chip. The trials are endless and designate caution in deliberation of RF Designs [1–3]. In Mixer in source circuitry is used to combine the Low frequency message signal with the locally generated signal to produce high frequency signal [4,5]. In the microelectronics applications, RF Integrated Circuits (RFICs) plays an improtant role due to the lower cost and less power operation in the 2.4 GHz frequency range. RF front end design contains Low Noise Amplifier (LNA), Mixer and Voltage Controlled Oscillator (VCO), and Power Amplifier (PA). Mixers, and LNAs are important blocks in transceivers. The output of mixer consists of sum and difference of input signal and Local Oscillator (LO) frequency. The block diagram depicts a simplified diagram of a base station transceiver in Fig. 1.
E-mail address: [email protected] https://doi.org/10.1016/j.micpro.2019.102850 0141-9331/© 2019 Published by Elsevier B.V.
This system contains receiver and a transmitter sections. In the receiver section, the signal would enter into the antenna. The signal usually becomes weak due to noise interference and attenuation at the antenna, and it needs to be properly arranged to enter the system. The LNA will amplify the desired signal while adding as little distortion as possible. Then the signal is sent to the down conversion mixer and low pass filter (LPF) which should be converted and tuned. The analog signal is then converted to digital data via the analog-to-digital converter (ADC). Finally, the bits of data are used for processing purposes. In the transmission section, the bits of data are converted from digital bits to analog signal by the digital-to-analog converter (DAC). The signal is then sent to up conversion mixer and high pass filter (HPF), which shifts the original frequency to a higher frequency for communication. The new signal is then sent to a power amplifier (PA) to increase the power for the signal, and prepare the signal for its distance travel. The signal is then transmitted though the antenna. LNA plays a key role in the receiver. It receives very low power from the antenna and amplifies them along with the decrease in the noise to a greater level. The demand of LNA rises due to the progress of the modern technologies such as GPS, Bluetooth, cell phones etc., Mostly in wireless communication system, the LNA is critical to design because it provides adequate gain from the little signal power which is established by the antenna, not only to make signal to noise ratio degradation but also to sustain signals with low power dissipation.
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Fig. 1. General RF transceiver block diagram.
Fig. 3. Basic single balanced mixer.
Fig. 2. Typical gain compression characteristic for a non-linear amplifier/mixer.
The performance of the LNA is mainly affected by three parameters namely the input impedance, gain and noise figure of the amplifier. The reduction of power consumption of radio frequency front end is the most important one in wireless communications. The basic structure of a single mixer is that it has two input port and one output port. It combines the carrier signal, either RF or intermediate frequency (IF) subject to up conversion or down conversion, with input from the local oscillator (LO).The properties of mixer are nonlinearity and time-variance. The operation is accomplished in time domain by multiplying two input signals:
x(t ) = A cos ω1 t
(1)
y(t ) = B cos ω2 t
(2)
Mixer output is
x(t ).y(t ) = A cos ω1 t.B cos ω2 t AB AB = cos(ω1 − ω2 )t + cos(ω1 + ω2 )t 2 2
(3)
The mixer output contains nonlinear components, which introduce more noise, and improper design may also cause leakage effects, which complicate the system design. The nonlinear characteristic of mixer is that if exceeding a certain input level causing a gain compression as shown in Fig. 2. Beyond this point the intermediate frequency fails to track the RF power at 1 dB upsurge in RF power will effect in a 1 dB upsurge in the close to IF power. There is a compromise between designing of mixer and LNA in rapports of the gain, noise figure, and power feeding. Single Balanced Gilbert cell mixer design operates is depicted in Fig. 3. The single wave RF signal first enters into the base of the transistor M1, while the LO signal is parted into the base transistors M2 and M3. The input RF signal is then transformed into current. The current signal is combined with the switching LO signals in M2 & M3. The resultant current is converted back into voltage
via the load resistors R1 & R2, then the output exits from the respective IF outputs. The ideal SB Gilbert cell appears to be very beneficial. This design contributes moderate good gain at a lower LO power and low power consumption; occasionally this specification can be compromised for further desired specifications. When a designer needs a higher gain and/or system linearity and it tends to tradeoff power consumption or even NF achieve that designs goal. It is illustrated that this design is not adequate powerful to encounter all the many mixer design specifications claimed by the communication industry. Even though the SB Gilbert cell mixer is a solid design and achieve the goals for some design systems, it may not be satisfactory for designs that call for increased mixer specifications. This is the place where the Double Balanced (DB) Gilbert cell mixer can meet those requirements. The most normally used active mixer architecture consists of DB Gilbert cell mixer, and comprises advances over other designs comprising the SB Gilbert cell mixer. The DB mixer can accomplish greater mixer provisions at the cost of a slight surge in NF and overall design power consumption. The normally doublebalanced mixer with Gilbert Cell is used in RFIC designs. Gilbert cell mixers are broadly used due to their practical conversion gain, linearity, isolation and noise figure. To expand the linearity of the mixer, many techniques and structures have been innovated. Use of these techniques has resulted in complex circuit with high power consumption, more noise, and higher cost. Simple LNA designs do not provide better noise performance. The proposed method is planned to design a mixer and LNA to attain extraordinary gain, little noise figure and reduced power consumption in 0.18 μm CMOS technology using Cadence Virtuoso tool. The proposed mixer circuit operates at a supply voltage of 1.8 V. The organizations of the paper are Section 2 describes existing methods, Section 3 explains the proposed designs, and Section 4 describes the results and discussion. Finally Section 5 concludes. 2. Existing methods The existing methods of LNA and mixer design approaches have been proposed in the past. All the approaches have its specific advantages and disadvantages. Several popular approaches are MultiTanh, current bleeding, Switched bias, Folded cascade, Bulk driven method, CCPD, MGTR for mixer design and Source degenerate LNA design for Low Noise Amplifier.
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Fig. 5. RF circuit with source degeneration. Fig. 4. Source degenerate LNA.
2.1. Source degenerate LNA The design of LNA involves compromise among gain, linearity, Noise Figure (NF) and power consumption. The design optimization technique is used to get tradeoff between gain and linearity. Different topologies of LNA are available. The source degenerated LNA is shown in the Fig. 4, inductance L1 which is at drain of M2 along with node capacitance vibrate at the operational frequency and offer M3 and it is also in current mirror linking with M1 and their ratio will govern the current through the cascade subdivision. The voltage across gate source of M1 is determined by the proper selection of width of M1. The value of the resistance R should be superior to the output impedance of prior juncture. The infinite input impedance is provided to the cascade by M1. The advantage of cascade is explained that it is bright to diminish the effect of gate to drain capacitance i.e., miller capacitance since the input resistance of M2 is considerably lesser than the output resistance of M1. By using power constraint noise optimization technique, the width of M1 is obtained. The parameters Lg and Ls, which are used for input impedance matching, are obtained by using equivalent small signal model. The mixer is described through its vigorous design parameter which consists of conversion gain, linearity, noise figure, and port isolation as [1–11]. The active mixer leads to a superior conversion gain and little noise figure with poorer the linearity and power consumption [12–16]. The RF input circuit of the mixer has been revised with auxiliary basis disintegration for enlightening the linearity of the double balance Gilbert cell mixer. Source degeneration circuit for mixer is shown in Fig. 5. In LNA, the resistances are comprehended as inductors Ls. The source resistor Rs prominently enriched the linearity of the mixer. But, resistor will produce a root for voltage drop and later a desired surge in the voltage barriers to confirm the devices endured in saturation. Additional crucial tricky using a resistor is producing the noise. The resolution is applied to use an inductor. There are numerals of concerns when using an inductor Ls, 1. The circuit will be extra frequency dependent. 2. Also the uses of inductors in CMOS incline to require low Quality (Q) factors – typically 2–3. 3. Source inductor will have a major consequence on the input impedance (Re) and necessity will be tested to safeguard the impedance is positive.
The CMOS down Conversion Gilbert mixer for wireless communication has been optimized to consume less power which is described as [17,18]. The Gilbert mixer cell topology is frequently employed for assembling active mixer [19–23]. The Gilbert cell is widely used because it provides extraordinary conversion gain, noble port-to-port isolation and small even-order distortion as [24]. A low power transceiver for Wireless Sensor Networks (WSN) is designed using a receiver, a fractional-N frequency synthesizer, and a class-E transmitter, and it is superior with output parameter such as sensitivity, power consumption, and silicon area which are described as [25]. The CMOS receiver architecture is combination of LNA and Mixer. The proposed architecture operates at 2.4 GHz RF frequency. An unconditionally stable Low Noise Amplifier for the L1 carrier of Global Positioning System (GPS) is working on the 1.57542 GHz band as [26]. Gilbert cell mixer proposal and action are described in [27]. CMOS receiver architecture with combined LNA and Mixer is presented as [28]. LNA and Mixer are designed using Cadence virtuoso tool at 180 nm technology. Differential LNA and Gilbert Mixer are also designed in order to achieve greater gain and small noise figure along with better conversion gain. The design of up-conversion mixer using the current mirror and current-bleeding with a simple degeneration resistor is presented as [29]. 3. Proposed method The proposed method describes the design of differential LNA, Single balanced mixer using current mirror along with BALUN and double balanced Gilbert cell mixer design using the BALUN along with the biasing and controlling MOSFETs, integrated design of differential LNA and double balanced Gilbert mixer. The motivation to design differential LNA is provided that it offers a stable reference point and noise reduction. Two single ended circuits are used to design one differential circuit. It uses the cascade design whereas the advantage of cascade has the ability to diminish the effect of gate to drain capacitance i.e., miller capacitance since the input resistance is much lesser than the output resistance. Gilbert mixer has numerous significant features that it is, sufficient conversion gain with suitable load. A better port-to-port isolation and little noise figure is obtained by double-Balanced Gilbert cell topology. It uses mechanism on the idea of trans linear structure. The shortcomings of this mixer have restricted linearity and frequency, which will be contingent on identical. The input transistors of these mixers should be in saturation region.
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3.1. Proposed method of differential LNA
From the circuit designed for plotting the DC response curve, gm value is found as,
The proposed method of differential LNA has been designed from two single ended source degenerated LNAs. It uses the cascade design whereas the benefit of cascade is enlisted that it is able to reduce the effect of gate to drain capacitance meanwhile the input resistance of M2 is much smaller than the output resistance of M1. The differential LNA has several important advantages when compared to single ended circuits. The key benefit of using differential LNA is described that it offers a steady reference point. The measured values of this LNA are constantly taken with respect to former half circuit. The foremost benefit of using this LNA over other topologies is noise reduction. Two single ended circuits are needed in order to create one differential circuit in which each transistor and circuit has complementary transistor.The positive voltage is given to the gate of first single ended circuit while negative voltage is given to the gate of second single ended circuit or else grounded. The use of source degeneration is to generate gate current noise and the total noise is toughly decrease by using a capacitance in shunt with the amplifying MOS transistor of the LNA. It upshots precise low noise figure and very low power consumption. So the differential LNA is chosen for receiver design. The positive-feedback loop is applied by adding couple capacitors between the drain and source of the output transistors and their value should be selected compromise with the gain and stability. The feedback capacitors can raise the chip size, but the gain can be improved at an ample greater rate than size. While choosing the input transistor’s size, a key design compromises the current concentration essential for least noise figure. The optimal width of the input transistors is selected to get best noise performance. 3.2. LNA specifications The LNA specifications of RF frequency (Input) = 2.4 GHz, noise figure <5 dB, gain >10 dB, supply voltage = 1.8 V are designed and simulated. 3.3. Mixer specifications RF frequency = 2.4 GHz, local oscillator (LO) frequency = 2.9 GHz intermediate frequency (IF) = 500 MHz, gain > 10 dB, noise figure <5 dB. 3.3.1. Design procedure for LNA The width of the M1 transistor can be found by,
1 W= 3.Cox.ω.Rs.L
(4)
∈ox 3.45 × 10−11 = = 8.42 × 10−3 F/m2 tox 4.1 × 10−9
(5)
where ɛox =ɛo . ɛr , hence the width of the transistor is,
3 × 8.42 × 10−3 × 2π × 2.4 × 109 × 50 × 180 × 10−9 = 291.7 μm The gate-source capacitance is calculated as given below.
Cgs =
2 × w × Cox × L 3
2 × 2.917 × 10−4 × 8.42 × 10−2 × 180 × 10−9 3 = 2.947 × 10−13
Cgs =
Substituting the values of gm and Cgs , Ls = 108.5 fH
f =
2π
1
(7)
(Ls + Lg ) × Cgs
The above equation can be rearranged to form the following equation,
1 = 14.92 nH Cgs × w2
Lg =
(8)
3.3.2. Design procedure for mixer The procedure involved in designing a mixer is furnished below, With voltage gain of 6 dB we can calculate gm, Conversion Gain
C.G =
2
π
RL Rs +
(9)
1 gm
Convert dB to conversion gain = 106/10 = 3.98
gm =
2
π
.
RL − RS Vgain
−1
(10)
Let RL = 500 , RS = 10 , gm = 0.01429 gm calculated and obtain W by assuming the minimum gate length to be 0.180 μm and a current of 2 mA,
w=
gm 2 .L 0.014292 × 0.180 = = 105 μm 2.k p .IDS 2 × 171 × 10−6 × 2 × 10−2
(11)
where k p = μ0 .Cox For the current mirror circuit the width of the transistor is 10 μm. 3.3.3. Design procedure for LPF Low pass filter with cut-off frequency of 500 MHz, the L and C values are calculated as follows,
Z0
L=
π × λc
=
500
π × 500 MHz
= 310 nH
(12)
where Z0 is characteristics impedance and λc is cutoff frequency
C=
1 1 = = 1270 fF Z0 × π × λc 500 × π × 500 M
(13)
The mixer has converts RF input voltage into current. The resultant current is then multiplied by the LO signal at the mixer. If the drive voltage at the LO port is large, the RF current will be efficiently multiplied with 50% duty cycle in which its frequency is that of the local oscillator. However the single-balanced mixer has port isolations and the conversion gain can be simply attuned and established on the gm and ZL. It has some drawbacks. 1. Signal density at output 2. RF unstable owed low noise immunity
1
w=
gm × Ls = 50 Cgs
3.4. Proposed method of single balanced Gilbert cell mixer
where Cox = Capacitance of the gate-oxide, Rs = Source resistance, L = length of the device, ω = angular frequency. The gate-oxide capacitance is found as follows,
Cox =
gm = 135.86 m,
(6)
These drawbacks are overcome by using current mirror and Balun circuit with existing mixer circuit as below. A current mirror circuit is used to copy a current through one active device by controlling the current in another active device of a circuit, keeping the output current constant irrespective of loading. An idyllic current mirror is merely a model of inverting current amplifier that reverses direction of the current. The current mirror is employed to give bias currents and active loads to circuits. It can model a more faithful current source. There are three key specifications of a current mirror are.
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1. The transfer ratio. 2. AC output resistance to define magnitude of the output current with the voltage applied. 3. The smallest voltage drops across the output of the mirror essential to create it work appropriately. A Current Mirror topology is present in the driver stage due to its non-linearity as well as the linearity of conventional Gilbert cell mixer is not worthy linear. Since current mirror topology is highly linear, it is used to produce much better linearity. A BALUN is an electrical device that alters between a balanced signal and an unbalanced signal. Transformer baluns can also be employed to join lines of contradictory impedance. Occasionally, in the case of transformer baluns, magnetic coupling is used but not necessities do it. Common-mode chokes are also used as baluns and work by eradicating, rather than overlooking, common mode signals. This mixer is suffered from IF leakage and second order effects. 3.5. Proposed method of double balanced Gilbert cell mixer Double Balanced Mixers are used to avoid the issues of single balanced mixer. It achieves high CG, linearity, and port isolation at the cost of a slight increase in NF and power consumption. DB Gilbert mixer is mainly a combination of two SB mixers and it is connected in antiparallel for LO and parallel for IF with source degeneration to get linearity and stability of the mixer. The LO terms sum to zero in the output; however the converted IF signal is doubled in the output. This mixer so offers a high degree of LO-IF isolation, drop of noise in the outputs, aiding filtering necessity at the output. Differential RF input in the transconductance part and switching operations consist of four transistors. Thus switching operation converts current into voltage. Balun is used to deliver single ended inputs and outputs and will thus combine the differential IF signals to provide a 3 dB rise in the differential conversion gain. Gates of the RF MOSFETS 1 & 6 are grounded via 10 K resistors that block any RF signal and to guarantee correct bias, the tail MOSFET 9 is connected to a negative supply. The tail current is set by the ‘bias’ variable. The DB mixer has better transconductance, thus it has higher CG. DB Gilbert cell has the control over the harmonic products to produce linearity. By adjusting the transistor stacking and setup is done for maintain port isolation. The number of transistor increases and improper switching of transistor leads to rise in NF and these transistors needs more supply. This increases the power consumption of DB mixer.
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means of a bond-wire. LG = 14.92 nm which is higher than L which is integrated inductor. The key improvement of this circuit is low area, due to the less number of components. The circuit has only two inductors. 4. Results and discussion The single balanced Gilbert cell mixer, double balanced Gilbert cell mixer, source degenerate LNA and differential LNA have been designed using Cadence Spectre_RF tool on TSMC 180 nm technology. Cadence EDA tools are used Virtuoso 64 for Schematic Editing and Spectre for Simulation. The Fig. 6 shows the schematic diagram of the source degenerate LNA with the input frequency of 2.4 GHz. The source degenerate LNA is used to design differential LNA which increases the linearity and stability. For the Source degenerate LNA, Gain and Noise Figure are obtain from s-parameter analysis and shown in the Fig. 7a and b respectively and about 10.8507 dB of Gain and ∼1 dB of Noise Figure with 179.8E−3 W at 2.4 GHz frequency. The Fig. 8a shows the schematic diagram of proposed differential LNA. Two single ended Source Degenerate LNAs are used to design a differential LNA with calculated values. From transient
Fig. 6. Schematic of source degenerate LNA.
3.6. Combined differential LNA and double balanced Gilbert cell mixer The low voltage and low power RFIC are implemented. It should accomplish low power dissipation in the front end of receiver. The detached blocks entail two translations, one from current to voltage at the LNA output, and the other from voltage to current at the mixer input. The multiple DC current paths in circuit are a major source of power consumption and it should be reduced by integrating the proper current-mirror design. The low noise amplifier LNA has a single ended topology which is followed by the double balanced mixer. The current mirror circuit and balun are used for integrating LNA and mixer. DB mixer is no port isolation at RF and IF port, so it does need complicated filters. It is also free from self-mixing of RF and LO signal. A low-pass filter is designed with cut off frequency of 500 MHz which has calculated value of L = 310 nm and capacitor C = 1270 fF is used to allow the desired frequency and other harmonics are attenuated. L requires typically a low value and can be realized by
Fig. 7. (a) Gain of source degenerate LNA. (b) Noise figure of source degenerate LNA.
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Fig. 9. (a) Gains of differential LNA. (b) Noise figure of differential LNA. Fig. 8. (a) Schematic of differential LNA. (b) Output of differential LNA.
response of LNA, it shows that the output voltage (green) which is amplified version of input voltage (Red) as in Fig. 8b. Fig. 9a shows the gain plot of the differential LNA and it is measured as 20.2852 dB at 1.8 V with 2.4 GHz by adjusting transistor size, passive components of the design. The noise figure of the differential LNA is obtained using scattering parameters. The graph in Fig. 9b shows that the LNA has a noise figure of 2.14547 dB at 1.8 V supply voltage, 2.4 GHz operating frequency. Since noise figure meets the specification. 4.1. Mixer results Fig. 10 shows the schematic diagram of the single balanced Gilbert cell mixer using the current mirror circuit and BALUN and its output. The transient response plot consists of the input RF = 2.4 GHz and LO frequencies = 3 GHz and the output IF frequency signals = 2.9 GHz with power = 206.2 nW. The IF signal is distorted, thus guided through a low pass filter. The final output through the filter is distortion less. The differential signal at LO, RF and IF are low. To boost these signal, A double balanced Gilbert mixer is designed and the results obtained at RF frequency are 2.4 GHz; LO frequency: 3 GHz; IF frequency: 6 GHz with power 140.4 nW, which are shown in Fig. 11. Double balanced mixer, both of differential transistors should be driven by the RF signal. The differential signal v1 and v2 are measured at LO, RF and IF are higher than the SB mixer results. The performance of DB mixer is higher than SB mixer. Source degenerate LNA is integrated with the double balanced Gilbert cell mixer to reduce the conversion losses and power dissipation due to DC sources. The designed LNA is single ended topology. So a balun
Fig. 10. (a) Schematic of single balanced Gilbert cell mixer. (b) Output schematic of single balanced Gilbert cell mixer.
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Fig. 11. (a) Schematic of double balanced Gilbert cell mixer. (b) Output of double balanced Gilbert cell mixer.
Fig. 13. (a) Schematic of differential LNA integrated with double balanced Gilbert cell mixer. (b) Output of differential LNA integrated with double balanced Gilbert cell mixer.
is used to transfer the single ended signal to a differential signal. The degradation of balun can be compensated by current mirror. Current mirror will boost the linearity of the circuit. Fig. 12 is the schematic of Source degenerate LNA which is integrated with the double balanced Gilbert cell mixer. RF input for LNA: 2.4 GHz; LO frequency input for mixer: 3 GHz; IF frequency: ∼6 MHz with power: 3.735 W. Output waveform is slightly distorted. This can be overcome by the integration of Differential LNA with the double balanced mixer and the Fig. 13 shows the schematic and the output with RF input for LNA: 2.4 GHz; LO frequency input for mixer: 3 GHz; IF frequency: ∼ 6 MHz with 3.747 W. The output of integration of Differential LNA with the double balanced mixer is distortion less. 5. Post-layout simulation results
Fig. 12. (a) Schematic of source degenerate LNA integrated with double balanced Gilbert cell mixer. (b) Output of source degenerate LNA integrated with double balanced Gilbert cell mixer.
The proposed LNA and mixer are designed by 180 nm technology, and simulated using Cadence SpectreRF simulator. Layout design of proposed differential LNA circuit is shown in Fig. 14a. Fig. 14b provides the output waveform for the proposed differential LNA. The layout has been drawn and the association of layers has been positioned as symmetrical as possible to drop mismatches. All of the components in this design, plus spiral inductors and metal-insulator-metal capacitors, are employed in on-chip. The parasitic resistances and capacitances are also removed from the layout and taken into account in simulation [27]. Fig. 15 shows the layout design and output respectively for the proposed double balanced Gilbert cell mixer. Table 1 illustrates the comparison between the source degenerate LNA and Differential LNA. From the table, it is observed that
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Fig. 14. (a) Layout design for proposed differential LNA. (b) Output of layout design of proposed differential LNA. Table 1 Comparisons of source degenerate and differential LNA. Parameters
Source degenerate LNA
Differential LNA
Noise figure Gain Power
2.14547 dB 10.8587 dB 179.8 mW
∼1 dB 20.2852 dB 167.1 mW Fig. 15. (a) Layout design for proposed double balanced mixer. (b) Output of layout design of proposed double balanced mixer.
the noise has been greatly reduced in the Differential LNA and the gain has been slightly increased with the increase in power consumption. Table 2 shows the comparison of the results obtained from the proposed methods of single and double balanced Gilbert cell mixers and the results obtained DB mixer is increase in IF frequency of 6 GHz with increase in power consumption. DB mixer is constructed using 2 SB mixers. Layout design and its output of both differential and double balanced mixer are obtained. The comparison of layout output waveform and simulated output waveform are almost equal. Integrated results of Source Degenerate LNA and DB Mixer are distorted transient response as compared that of Differential
LNA and DB Mixer. Differential LNA and DB Mixer with current mirror, bias circuit, filter and balun are integrated. The results of later is show noiseless transient response with almost same power. The cross comparison results are shown in Table 3. The conversion gain of 22.28 dB and IF frequency 595 MHz of Differential LNA with Double Balanced mixer are higher than the cross comparison results of the other methods at 180 nm technology. Table 3 shows the cross platform comparison of proposed mixer with existing. The results show that the proposed method outperforms compared with existing methods.
Table 2 Results obtained from the integration of LNA and mixer. Parameters
SB Gilbert cell mixer
DB Gilbert cell mixer
Source degenerate LNA + DB mixer
Differential LNA + DB mixer
RF (GHz) LO-frequency GHz IF frequency GHz Power
2.4 3 2.9 206.2 n W
2.4 3 6 140.4 μ W
2.4 3 0.588 3.735 W
2.4 3 0.595 3.747 W
Table 3 Cross platform comparative performance. Parameters
2
3
4
9
10
19
Differential LNA with DB mixer
Technology μm Power supply (V) IF freq (MHz) LO freq (GHz) RF freq (GHz) Conversion gain (dB)
0.18 1.2 100 1.8 1.9 5
0.13 1.2 10–400 1.8–2.6 1.810 1.1
0.18 1.8 1 2.419 2.42 16.2
0.18 1.8 100 5.1 5.2 6
0.18 1.8 100 5.1 5.2 6
90 nm 1.8 100 2.3 2.4 21.4
0.18 1.8 595 3 2.4 22.28
C. Kalamani / Microprocessors and Microsystems 71 (2019) 102850
6. Conclusions A single stranded source degenerate LNA, a differential LNA, a single and a double balanced Gilbert cell mixers are designed and simulated. From the results obtained, it is concluded that the Noise has been greatly reduced while using proposed method of Differential LNA along with little increase in gain and power consumption. Single balanced Gilbert cell mixers will not provide a desired output for all the frequency ranges. It is confined only to higher frequencies and it is not accurate for many lower frequencies. The linearity and gain are less for single balanced mixer. In order to overcome this, Double balanced Gilbert cell mixer is designed. Usually power consumption and noise will be higher in these double balanced structures although they provide high gain and linearity. Further, optimization will improve its performance. This will find its application in the RF frequency range, ISM band and many. Finally, the differential LNA and the double balanced mixer are integrated to provide the better performance. Declaration of Competing Interest We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. References [1] [2] [3] [4]
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