- Email: [email protected]
Current-mode current-tunable four-phase quadrature oscillator
G Model IJLEO-54940; No. of Pages 4
ARTICLE IN PRESS Optik xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Current-mode current-tunable four-phase quadrature oscillator Shiqiang Chen a,b,∗ , Junfeng Wang b a b
College of Computer Science, Sichuan University, Chengdu, PR China Hubei University for Nationalities, Enshi, PR China
a r t i c l e
i n f o
Article history: Received 8 November 2013 Accepted 6 June 2014 Available online xxx Keywords: Circuit Current mode Current differencing transconductance amplifiers Quadrature oscillator
a b s t r a c t A current-mode current-tunable four-phase quadrature oscillator (QO) using current differencing transconductance amplifiers (CDTA) is presented in this paper. The proposed QO consists of three CDTAs and two grounded capacitors, which can provide four quadrature current outputs at high impedance nodes. The proposed QO has the advantages of electronically and independently control of oscillation condition and oscillation frequency. Moreover, the active and passive sensitivities of the QO are low. Cadence IC Design Tools 5.1.41 post-layout simulation results are included to confirm the theory. © 2014 Elsevier GmbH. All rights reserved.
1. Introduction As the current-mode circuits have the advantages of low power consumption, inherently wide bandwidth and larger dynamic range, they have received considerable attention [1]. The current differencing transconductance amplifier (CDTA) is a recently introduced current mode building block by Biolek in 2003 [2]. It is a really current-mode element whose input and output are current form, and it is widely used in designing active filters [3–8], current limiters [9], oscillators [10] and many other analog signal processing circuits. The CDTA-based quadrature oscillators are reported in Refs. [11–19]. However, the works in Refs. [11–18] cannot provide electronically controlled CO and FO, which cannot be used as variable frequency oscillator; the works in Refs. [11,12,16] suffer from floating capacitors, and the work in Refs. [11–14,17,18] use resistors, and they are not suitable for monolithic integration; the BJT technology is used in Ref. [19], and it is not compatible with the CMOS digital integrated circuit to realize monolithically integration. In this paper, a new CDTA-based current-mode four-phase QO with three CDTAs and two grounded capacitors is presented. The attractive advantage of the proposed QO is the condition of oscillation (CO) and frequency of oscillation (FO) of the quadrature oscillator can be adjusted electronically and independently by a
∗ Corresponding author at: College of Computer Science, Sichuan University, Chengdu, PR China. E-mail address: [email protected] (S. Chen).
bias voltage, and it is suitable for variable frequency oscillator (VFO). Moreover, the proposed QO is completely resistor-less, and it can provide four quadrature outputs at high impedance nodes. The performance of the proposed QO is demonstrated by Cadence IC Design Tools 5.1.41 post-layout simulation results. 2. Theory and principle 2.1. Current differencing transconductance amplifiers Fig. 1a shows the symbol of CDTA, and Fig. 1b is the equivalent circuit of the CDTA. The terminal relations of the CDTA can be characterized by the following set of equations [4]:
⎧ ⎪ ⎪ ⎪ ⎪ ⎨
vp = vn = 0 iz = ip − in
⎪ ix + = gm vz = gm ZZ iZ ⎪ ⎪ ⎪ ⎩
(1)
ix − = −gm vz = −gm ZZ iZ
In Fig. 1, p and n are the input terminals, z and x are the output terminals, gm is the transconductance gain, and Zz is the external impedance connected to the terminal Z. From Eq. (1), the current iz is the difference of the currents at p and n (ip − in ), and it flows from the terminal z into the impedance Zz. The voltage at the terminal z is transferred to a current at the terminal x (ix ) by a transconductance gain (gm ), which can be electronically controlled by an external bias current Ib . The CDTA used in this work is shown in Fig. 2.
http://dx.doi.org/10.1016/j.ijleo.2014.06.142 0030-4026/© 2014 Elsevier GmbH. All rights reserved.
Please cite this article in press as: S. Chen, J. Wang, Current-mode current-tunable four-phase quadrature oscillator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.142
G Model
ARTICLE IN PRESS
IJLEO-54940; No. of Pages 4
S. Chen, J. Wang / Optik xxx (2014) xxx–xxx
2
Vp
Ib
ip p
x-
ix -
Vz
p ip
gmVz x+
z
CDTA n
Vn in
z
x+
i x+
Z
n in
-gmVz
ip-in
Because the CDTA can provide multiple outputs, and another two inverted output currents io3 and io4 can be obtained easily. Thus, the relations of all the output currents can be expressed as:
x-
io1 = −io3
(6)
io2 = −io4
Iz (a) Symbol for the CDTA
From Eqs. (5) and (6), it is clear that the proposed QO can provide four quadrature current outputs.
(b) Ideal model of the CDTA
Fig. 1. Symbol and ideal model of CDTA.
3. Non-ideal analysis Taking the tracking errors of the CDTA into account, the port relations of the non-ideal CDTA can be rewritten as:
⎧ v = vn = 0 ⎪ ⎨ p ⎪ ⎩
iz = ˛p ip − ˛n in
(7)
ix + = ˇgm vz
where ˛p = 1 − εp denotes the current tracking error from terminal p to z, ˛n = 1 − εn denotes the current tracking error from terminal n to z, and ˇ is transconductance inaccuracy factor from the z to x terminals of the CDTA, respectively. Taking the non-idealities in Eq. (7) into account, the non-ideal characteristic equation of the QO can be expressed as:
Fig. 2. CMOS-based CDTA in this work [15].
2.2. The proposed current mode quadrature oscillator
s2 C1 C2 + s(˛n2 ˇ2 gm2 − ˛p2 ˇ1 gm1 )C2 + ˛p1 ˛n3 ˇ2 ˇ3 gm2 gm3 = 0 (8) Fig. 3 is the proposed four-phase quadrature oscillator, which employs three CDTAs and two grounded capacitors. The grounded capacitors used in the QO are effective to eliminate various of parasitic capacitance. A routine circuit analysis using Eq. (1), we can get the characteristic equation of the QO is: 2
s C1 C2 + s(gm2 − gm1 )C2 + gm2 gm3 = 0
ωo =
(3)
gm2 gm3 C1 C2
(4)
From Eqs. (3) and (4), it can be seen that the CO can be adjusted independently by the transconductance gm1 without disturbing the FO; the FO can be tuned independently by the transconductance gm3 without disturbing the CO. From Fig. 3, the current transfer function between io1 and io2 is: io1 (s) io1 (jω) gm2 gm2 −j90◦ = e = = sC2 ωC2 io2 (s) io2 (jω)
ωo =
(5)
(9)
˛p1 ˛n3 ˇ2 ˇ3 gm2 gm3 C1 C2
(10)
where ˛pi , ˛ni and ˇi are the parameters ˛p , ˛n and ˇ of the i-th CDTA, respectively. It can be seen from Eqs. (9) and (10) that if the tracking errors of CDTA1 and CDTA2 are equal, the CO of the proposed QO will not be affected; however, the FO of the QO will deviate from the ideal value, because of the tracking errors. In this case, the deviation of the FO can be compensated by trimming the transconductance gm3 . From Eq. (10), the active and passive sensitivities of ωo are low, and they can be expressed as:
⎧ 1 ⎪ S ωo = ⎪ ⎪ gm2 ,gm3 ,˛p1 ,˛n3 ,ˇ2 ,ˇ3 2 ⎨ ⎪ ⎪ ⎪ ⎩
Sgωo
m1 ,˛n1 ,˛p2 ,˛n2 ,˛p3 ,ˇ1
SCωo,C = − 1
So, the phase difference between io1 and io2 is 90◦ , and the two currents are quadrature.
Fig. 3. The proposed current-mode QO.
˛n2 ˇ2 gm2 = ˛p2 ˇ1 gm1
(2)
where gm1 , gm2 and gm3 are the transconductance of the CDTA1 , CDTA2 and CDTA3 , respectively. From Eq. (2), the CO and FO of the QO can be expressed as: gm2 = gm1
The CO and FO of the proposed QO get modified and are given as:
2
=0
(11)
1 2
4. Post-layout simulation results The proposed QO is verified using Cadence IC Design Tools 5.1.41 Spectre simulator with standard Charted 0.18 m CMOS technology. The chip layout design strictly obeys the Chartered Design Rule (YI-093-DR001 Rev1V 1.8V-3.3V) and Chartered Spice Model spec(yi093dr001 1v 00 20090731a), and it is designed as symmetrically as possible to minimize the mismatch in the signal paths. In the post-layout simulation, the supply voltage is ±1.2 V, the bias voltages Vb2 = −0.7 V, the capacitors C1 = 8 pF, C2 = 19 pF. Fig. 4 is the simulated Vo1 , Vo2 , Vo3 and Vo4 during initial state with 500 load resistors, and it is clear that the starting time of the proposed QO is about 0.25 s; Fig. 5 is the simulated quadrature outputs Vo1 , Vo2 , Vo3 and Vo4 from 0.5 s to 0.525 s with 500 load resistors.
Please cite this article in press as: S. Chen, J. Wang, Current-mode current-tunable four-phase quadrature oscillator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.142
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ARTICLE IN PRESS S. Chen, J. Wang / Optik xxx (2014) xxx–xxx
Fig. 4. The simulated Vo1 , Vo2 , Vo3 and Vo4 during initial state with 500 load resistors.
3
Fig. 7. The phase noise of the quadrature oscillator.
Fig. 8. The output frequency versus the bias voltage of CDTA3 . Fig. 5. The simulated quadrature outputs Vo1 , Vo2 , Vo3 and Vo4 with 500 load resistors.
Fig. 6 is the harmonic balance post-layout simulation result of Vo1 . From Fig. 6, we can know that the post-layout simulated frequency of the QO is about 74.23 MHz, and the output power of Vo1 is about −9.46 dBm, the output power of other harmonic signals are relatively small. Fig. 7 is the phase noise of the QO. The phase noise of the QO at 1 MHz offset is −84.29 dBc/Hz while the carrier is 74.23 MHz. Because the proposed QO has the attractive advantage of independently adjusting the FO by the transconductance of CDTA3 without disturbing the CO, the output frequency versus the bias voltage of CDTA3 is presented in Fig. 8. From Fig. 8, it is clear that the output frequency tuning range of the QO is about 41.71 MHz when
Fig. 6. The harmonic balance simulation result of Vo1 .
the control voltage changing from −1.2 V to −0.1 V, which means that the proposed QO can be used as variable frequency oscillator (VFO). The layout of the proposed QO is presented in Fig. 9. The QO takes a compact chip area of 1.1 mm2 including the testing pads. 5. Experimental evidence The QO in Fig. 3 is further verified in the laboratory with commercially available ICs AD844 and CA3080. Fig. 10 is the block diagram of realizing the CDTA using AD844 and CA3080. The current differencing unit is realized using the two AD844 ICs, and the two CA3080 ICs realize the transconductance section of the CDTA.
Fig. 9. The layout of the proposed QO (1.0 mm × 1.1 mm).
Please cite this article in press as: S. Chen, J. Wang, Current-mode current-tunable four-phase quadrature oscillator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.142
G Model
ARTICLE IN PRESS
IJLEO-54940; No. of Pages 4
S. Chen, J. Wang / Optik xxx (2014) xxx–xxx
4
p
CA3080
AD844 +
n
-
AD844 +
+x
+ zw
z
+
w
gm
Acknowledgement
gm
-
Design Tools post-layout simulation results show that the output frequency tuning range of the QO is about 41.71 MHz, and it can be used as VFO. Moreover, because of only grounded capacitors used in the QO, the proposed circuit is suitable for monolithic integrated circuit, and it only takes a compact chip area of 1.1 mm2 including the testing pads.
-x
CA3080 z Fig. 10. Possible implementation of CDTA using commercially available Ics.
Fig. 11. Experimental results of the four quadrature outputs.
Fig. 11 is the experimental results of the four quadrature output waveforms of Fig. 3 using the commercially available ICs. Fig. 11 provides the necessary and quite genuine experimental evidence to the proposed quadrature oscillator. 6. Conclusion A CDTA-based current-mode current-tunable four-phase quadrature oscillator is presented in this work. The Cadence IC
This work was supported in part by the National Natural Science Foundation of China under Grant 11102124. References [1] C. Toumazou, F.J. Lidjey, D. Haigh, Analog IC Design: The Current-Mode Approach, Peter Peregrinus Press, UK, 1990. [2] D. Biolek, CDTA – building block for current-mode analog signal processing, in: Proc. ECCTD’03, Vol. 3, 2003, pp. 397–400. [3] T. Dumawipata, W. Tangsrirat, W. Surakampontorn, Current-mode universal filter with four inputs and one output using CDTAs, in: IEEE Asia Pacific Conference on Circuits and Systems, Singapore, 2006, pp. 892– 895. [4] A.U. Keskin, D. Biolek, E. Hancioglu, V. Biolkova, Current-mode KHN filter employing current differencing transconductance amplifiers, Int. J. Electron. Commun. (AEÜ) 60 (2006) 443–446. [5] T. Dumawipata, W. Tangsrirat, W. Surakampontorn, Cascadable current-mode multifunction filter with two inputs and three outputs using CDTAs, in: 6th International Conference on Information, Communications & Signal Processing, Singapore, 2009, pp. 1–4. [6] F. Kacar, H.H. Kuntman, A new, improved CMOS realization of CDTA and its filter applications, Turk. J. Electr. Eng. Comput. Sci. 19 (2011) 632– 642. [7] N.A. Shah, M. Quadri, S.Z. Iqbal, CDTA based universal transadmittance filter, Analog Integr. Circuits Signal Process. 52 (2007) 65–69. [8] M. Siripruchyanun, W. Jaikla, Electronically controllable current-mode universal biquad filter using single DO-CCCDTA, Circuits Syst. Signal Process. 27 (2008) 113–122. [9] W. Tangsrirat, Synthesis of current differencing transconductance amplifierbased current limiters and its applications, J. Circuits Syst. Comput. 20 (2011) 185–206. [10] L. Yongan, A new single MCCCDTA based Wien-bridge oscillator with AGC, Int. J. Electron. Commun. (AEÜ) 66 (2012) 153–156. [11] A.U. Keskin, D. Biolek, Current mode quadrature oscillator using current differencing transconductance amplifiers (CDTA), IEE Proc. – Circuits Devices Syst. 153 (2006) 214–218. [12] A. Uygur, H. Kuntman, CDTA-based quadrature oscillator design, in: 14th European Signal Processing Conference (EUSIPCO 2006), Florence, Italy, 2006, pp. 4–8. [13] A. Lahiri, New current-mode quadrature oscillators using CDTA, IEICE Electron. Express 6 (2009) 135–140. [14] A. Lahiri, Novel voltage/current-mode quadrature oscillator using current differencing transconductance amplifier, Analog Integr. Circuits Signal Process. 61 (2009) 199–203. [15] W. Jaikla, A. Lahiri, Resistor-less current-mode four-phase quadrature oscillator using CCCDTAs and grounded capacitors, Int. J. Electron. Commun. (AEÜ) 66 (2012) 214–218. [16] W. Tangsrirat, T. Pukkalanun, W. Surakampontorn, Resistorless realization of current-mode first-order allpass filter using current differencing transconductance amplifiers, Microelectron. J. 41 (2010) 178–183. [17] D. Prasad, D.R. Bhaskar, A.K. Singh, Electronically controllable grounded capacitor current-mode quadrature oscillator using single MO-CCCDTA, Radioengineering 20 (2011) 354–359. [18] D. Biolek, A.U. Keskin, V. Biolkova, Grounded capacitor current mode SRCO using single modified CDTA, IET Circuits Devices Syst. 4 (2010) 496– 502. [19] W. Tangsrirat, W. Tanjaroen, Current-mode sinusoidal quadrature oscillator with independent control of oscillation frequency and condition using CDTAs, Indian J. Pure Appl. Phys. (IJPAP) 48 (2010) 363– 366.
Please cite this article in press as: S. Chen, J. Wang, Current-mode current-tunable four-phase quadrature oscillator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.142
ARTICLE IN PRESS Optik xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Current-mode current-tunable four-phase quadrature oscillator Shiqiang Chen a,b,∗ , Junfeng Wang b a b
College of Computer Science, Sichuan University, Chengdu, PR China Hubei University for Nationalities, Enshi, PR China
a r t i c l e
i n f o
Article history: Received 8 November 2013 Accepted 6 June 2014 Available online xxx Keywords: Circuit Current mode Current differencing transconductance amplifiers Quadrature oscillator
a b s t r a c t A current-mode current-tunable four-phase quadrature oscillator (QO) using current differencing transconductance amplifiers (CDTA) is presented in this paper. The proposed QO consists of three CDTAs and two grounded capacitors, which can provide four quadrature current outputs at high impedance nodes. The proposed QO has the advantages of electronically and independently control of oscillation condition and oscillation frequency. Moreover, the active and passive sensitivities of the QO are low. Cadence IC Design Tools 5.1.41 post-layout simulation results are included to confirm the theory. © 2014 Elsevier GmbH. All rights reserved.
1. Introduction As the current-mode circuits have the advantages of low power consumption, inherently wide bandwidth and larger dynamic range, they have received considerable attention [1]. The current differencing transconductance amplifier (CDTA) is a recently introduced current mode building block by Biolek in 2003 [2]. It is a really current-mode element whose input and output are current form, and it is widely used in designing active filters [3–8], current limiters [9], oscillators [10] and many other analog signal processing circuits. The CDTA-based quadrature oscillators are reported in Refs. [11–19]. However, the works in Refs. [11–18] cannot provide electronically controlled CO and FO, which cannot be used as variable frequency oscillator; the works in Refs. [11,12,16] suffer from floating capacitors, and the work in Refs. [11–14,17,18] use resistors, and they are not suitable for monolithic integration; the BJT technology is used in Ref. [19], and it is not compatible with the CMOS digital integrated circuit to realize monolithically integration. In this paper, a new CDTA-based current-mode four-phase QO with three CDTAs and two grounded capacitors is presented. The attractive advantage of the proposed QO is the condition of oscillation (CO) and frequency of oscillation (FO) of the quadrature oscillator can be adjusted electronically and independently by a
∗ Corresponding author at: College of Computer Science, Sichuan University, Chengdu, PR China. E-mail address: [email protected] (S. Chen).
bias voltage, and it is suitable for variable frequency oscillator (VFO). Moreover, the proposed QO is completely resistor-less, and it can provide four quadrature outputs at high impedance nodes. The performance of the proposed QO is demonstrated by Cadence IC Design Tools 5.1.41 post-layout simulation results. 2. Theory and principle 2.1. Current differencing transconductance amplifiers Fig. 1a shows the symbol of CDTA, and Fig. 1b is the equivalent circuit of the CDTA. The terminal relations of the CDTA can be characterized by the following set of equations [4]:
⎧ ⎪ ⎪ ⎪ ⎪ ⎨
vp = vn = 0 iz = ip − in
⎪ ix + = gm vz = gm ZZ iZ ⎪ ⎪ ⎪ ⎩
(1)
ix − = −gm vz = −gm ZZ iZ
In Fig. 1, p and n are the input terminals, z and x are the output terminals, gm is the transconductance gain, and Zz is the external impedance connected to the terminal Z. From Eq. (1), the current iz is the difference of the currents at p and n (ip − in ), and it flows from the terminal z into the impedance Zz. The voltage at the terminal z is transferred to a current at the terminal x (ix ) by a transconductance gain (gm ), which can be electronically controlled by an external bias current Ib . The CDTA used in this work is shown in Fig. 2.
http://dx.doi.org/10.1016/j.ijleo.2014.06.142 0030-4026/© 2014 Elsevier GmbH. All rights reserved.
Please cite this article in press as: S. Chen, J. Wang, Current-mode current-tunable four-phase quadrature oscillator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.142
G Model
ARTICLE IN PRESS
IJLEO-54940; No. of Pages 4
S. Chen, J. Wang / Optik xxx (2014) xxx–xxx
2
Vp
Ib
ip p
x-
ix -
Vz
p ip
gmVz x+
z
CDTA n
Vn in
z
x+
i x+
Z
n in
-gmVz
ip-in
Because the CDTA can provide multiple outputs, and another two inverted output currents io3 and io4 can be obtained easily. Thus, the relations of all the output currents can be expressed as:
x-
io1 = −io3
(6)
io2 = −io4
Iz (a) Symbol for the CDTA
From Eqs. (5) and (6), it is clear that the proposed QO can provide four quadrature current outputs.
(b) Ideal model of the CDTA
Fig. 1. Symbol and ideal model of CDTA.
3. Non-ideal analysis Taking the tracking errors of the CDTA into account, the port relations of the non-ideal CDTA can be rewritten as:
⎧ v = vn = 0 ⎪ ⎨ p ⎪ ⎩
iz = ˛p ip − ˛n in
(7)
ix + = ˇgm vz
where ˛p = 1 − εp denotes the current tracking error from terminal p to z, ˛n = 1 − εn denotes the current tracking error from terminal n to z, and ˇ is transconductance inaccuracy factor from the z to x terminals of the CDTA, respectively. Taking the non-idealities in Eq. (7) into account, the non-ideal characteristic equation of the QO can be expressed as:
Fig. 2. CMOS-based CDTA in this work [15].
2.2. The proposed current mode quadrature oscillator
s2 C1 C2 + s(˛n2 ˇ2 gm2 − ˛p2 ˇ1 gm1 )C2 + ˛p1 ˛n3 ˇ2 ˇ3 gm2 gm3 = 0 (8) Fig. 3 is the proposed four-phase quadrature oscillator, which employs three CDTAs and two grounded capacitors. The grounded capacitors used in the QO are effective to eliminate various of parasitic capacitance. A routine circuit analysis using Eq. (1), we can get the characteristic equation of the QO is: 2
s C1 C2 + s(gm2 − gm1 )C2 + gm2 gm3 = 0
ωo =
(3)
gm2 gm3 C1 C2
(4)
From Eqs. (3) and (4), it can be seen that the CO can be adjusted independently by the transconductance gm1 without disturbing the FO; the FO can be tuned independently by the transconductance gm3 without disturbing the CO. From Fig. 3, the current transfer function between io1 and io2 is: io1 (s) io1 (jω) gm2 gm2 −j90◦ = e = = sC2 ωC2 io2 (s) io2 (jω)
ωo =
(5)
(9)
˛p1 ˛n3 ˇ2 ˇ3 gm2 gm3 C1 C2
(10)
where ˛pi , ˛ni and ˇi are the parameters ˛p , ˛n and ˇ of the i-th CDTA, respectively. It can be seen from Eqs. (9) and (10) that if the tracking errors of CDTA1 and CDTA2 are equal, the CO of the proposed QO will not be affected; however, the FO of the QO will deviate from the ideal value, because of the tracking errors. In this case, the deviation of the FO can be compensated by trimming the transconductance gm3 . From Eq. (10), the active and passive sensitivities of ωo are low, and they can be expressed as:
⎧ 1 ⎪ S ωo = ⎪ ⎪ gm2 ,gm3 ,˛p1 ,˛n3 ,ˇ2 ,ˇ3 2 ⎨ ⎪ ⎪ ⎪ ⎩
Sgωo
m1 ,˛n1 ,˛p2 ,˛n2 ,˛p3 ,ˇ1
SCωo,C = − 1
So, the phase difference between io1 and io2 is 90◦ , and the two currents are quadrature.
Fig. 3. The proposed current-mode QO.
˛n2 ˇ2 gm2 = ˛p2 ˇ1 gm1
(2)
where gm1 , gm2 and gm3 are the transconductance of the CDTA1 , CDTA2 and CDTA3 , respectively. From Eq. (2), the CO and FO of the QO can be expressed as: gm2 = gm1
The CO and FO of the proposed QO get modified and are given as:
2
=0
(11)
1 2
4. Post-layout simulation results The proposed QO is verified using Cadence IC Design Tools 5.1.41 Spectre simulator with standard Charted 0.18 m CMOS technology. The chip layout design strictly obeys the Chartered Design Rule (YI-093-DR001 Rev1V 1.8V-3.3V) and Chartered Spice Model spec(yi093dr001 1v 00 20090731a), and it is designed as symmetrically as possible to minimize the mismatch in the signal paths. In the post-layout simulation, the supply voltage is ±1.2 V, the bias voltages Vb2 = −0.7 V, the capacitors C1 = 8 pF, C2 = 19 pF. Fig. 4 is the simulated Vo1 , Vo2 , Vo3 and Vo4 during initial state with 500 load resistors, and it is clear that the starting time of the proposed QO is about 0.25 s; Fig. 5 is the simulated quadrature outputs Vo1 , Vo2 , Vo3 and Vo4 from 0.5 s to 0.525 s with 500 load resistors.
Please cite this article in press as: S. Chen, J. Wang, Current-mode current-tunable four-phase quadrature oscillator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.142
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ARTICLE IN PRESS S. Chen, J. Wang / Optik xxx (2014) xxx–xxx
Fig. 4. The simulated Vo1 , Vo2 , Vo3 and Vo4 during initial state with 500 load resistors.
3
Fig. 7. The phase noise of the quadrature oscillator.
Fig. 8. The output frequency versus the bias voltage of CDTA3 . Fig. 5. The simulated quadrature outputs Vo1 , Vo2 , Vo3 and Vo4 with 500 load resistors.
Fig. 6 is the harmonic balance post-layout simulation result of Vo1 . From Fig. 6, we can know that the post-layout simulated frequency of the QO is about 74.23 MHz, and the output power of Vo1 is about −9.46 dBm, the output power of other harmonic signals are relatively small. Fig. 7 is the phase noise of the QO. The phase noise of the QO at 1 MHz offset is −84.29 dBc/Hz while the carrier is 74.23 MHz. Because the proposed QO has the attractive advantage of independently adjusting the FO by the transconductance of CDTA3 without disturbing the CO, the output frequency versus the bias voltage of CDTA3 is presented in Fig. 8. From Fig. 8, it is clear that the output frequency tuning range of the QO is about 41.71 MHz when
Fig. 6. The harmonic balance simulation result of Vo1 .
the control voltage changing from −1.2 V to −0.1 V, which means that the proposed QO can be used as variable frequency oscillator (VFO). The layout of the proposed QO is presented in Fig. 9. The QO takes a compact chip area of 1.1 mm2 including the testing pads. 5. Experimental evidence The QO in Fig. 3 is further verified in the laboratory with commercially available ICs AD844 and CA3080. Fig. 10 is the block diagram of realizing the CDTA using AD844 and CA3080. The current differencing unit is realized using the two AD844 ICs, and the two CA3080 ICs realize the transconductance section of the CDTA.
Fig. 9. The layout of the proposed QO (1.0 mm × 1.1 mm).
Please cite this article in press as: S. Chen, J. Wang, Current-mode current-tunable four-phase quadrature oscillator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.142
G Model
ARTICLE IN PRESS
IJLEO-54940; No. of Pages 4
S. Chen, J. Wang / Optik xxx (2014) xxx–xxx
4
p
CA3080
AD844 +
n
-
AD844 +
+x
+ zw
z
+
w
gm
Acknowledgement
gm
-
Design Tools post-layout simulation results show that the output frequency tuning range of the QO is about 41.71 MHz, and it can be used as VFO. Moreover, because of only grounded capacitors used in the QO, the proposed circuit is suitable for monolithic integrated circuit, and it only takes a compact chip area of 1.1 mm2 including the testing pads.
-x
CA3080 z Fig. 10. Possible implementation of CDTA using commercially available Ics.
Fig. 11. Experimental results of the four quadrature outputs.
Fig. 11 is the experimental results of the four quadrature output waveforms of Fig. 3 using the commercially available ICs. Fig. 11 provides the necessary and quite genuine experimental evidence to the proposed quadrature oscillator. 6. Conclusion A CDTA-based current-mode current-tunable four-phase quadrature oscillator is presented in this work. The Cadence IC
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Please cite this article in press as: S. Chen, J. Wang, Current-mode current-tunable four-phase quadrature oscillator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.142