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Integrated Readout Circuit Using Active Bridge For Resistive-Based Sensing
Available online at www.sciencedirect.com
ScienceDirect Procedia Computer Science 76 (2015) 430 – 435
2015 IEEE International Symposium on Robotics and Intelligent Sensors (IRIS 2015)
Integrated Readout Circuit Using Active Bridge For Resistivebased Sensing Nur Izzati Mohd Fauzi, Nur Farahin Anuar, Sukreen Hana Herman, Wan Fazlida Hanim Abdullah* Faculty of Electrical Engineering, Universiti Teknologi Mara , 40450 Shah Alam, Selangor
Abstract An integrated Readout Interfacing Circuit (ROIC) for resistive-based sensors using SILTERRA CMOS 0.13 μm technology that reads resistance shift and converts it to voltage was designed. In conventional practice, resistive-based sensors are interfaced with Wheatstone bridge to transform the sensor signal to voltage. Due to low sensitivity of Wheatstone bridge, the output voltage of shifted resistance is not significant. The objective of this project is to propose an integrated interfacing circuit using Wheatstone bridge with improved sensitivity. The project scope focuses on integrated circuit design of readout circuitry for resistive-based sensors. An active bridge, a modification of standard Wheatstone bridge using active components was used as ROIC. The sensitivity of the circuit is defined as percentage change in output voltage of the circuit to the changes in resistance of the sensor. Results show that, the active bridge circuit is almost four times more sensitive compare to conventional bridge circuit. The sensitivity improvement would allow any resistive-based sensors to be integrated with ROIC to produce more significant output voltage of shifted resistance. Keywords:Integrated Circuit, Readout Interfacing Circuit; Resistive-based Sensor; Sensitivity
1. Introduction Nowadays, robotics tactile sensor systems become more important, due to the demand for collision safety and reactive control in unstructured environments. Based on readings, there are three major classes that can measure principle of the tactile sensor cells which are optical, capacitive and resistive effects 1. Resistive are some of the common sensor because of relatively inexpensive to manufacture and easy to
* Corresponding author. Tel.: +60 19-2217347. E-mail address:[email protected]
1877-0509 © 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of the 2015 IEEE International Symposium on Robotics and Intelligent Sensors (IRIS 2015) doi:10.1016/j.procs.2015.12.284
Nur Izzati Mohd Fauzi et al. / Procedia Computer Science 76 (2015) 430 – 435
interface with signal conditioning circuit2. A resistive-based sensor is a category of sensors that acquire information through physical or environmental change. The measured characteristics can be properties such as temperature, vibration, shape, and normal forces. Tactile sensor may also measure one or more of these properties. Read-out Interfacing Circuit (ROIC) refers to the integrated circuit that is specifically used reading detectors of a sensitivity that is very low. Discrete circuit may not be useful as noise may be large enough to cover up whole signal. Voltage dividers and Wheatstone Bridge followed by differential or instrumentation amplifier are common conditioning circuit for resistive sensor in which an output signal is obtained3,4. Therefore, a voltage-mode Wheatstone bridge (VMWB) is employed for firstly interfacing resistive sensors in analog system. It is used to compare the signal to some set point value. The conventional Wheatstone bridge as the main topologies for resistive sensors offers an attractive for measuring small resistance and widely used in2,5. A. De Marcellis et al6, present a new approach based on current signals, suitable for the detection of very low variations of resistive sensors in a Wheatstone bridge configuration. One of the paper shows discussion on the force-balance Wheatstone bridge when interface with resistive-based sensor7. The project scope of this paper is comparing the sensitivity of balance Wheatstone bridge with voltage divider that to be used as conditioning circuit for resistive sensor. Due to low power supply rejection ratio (PSRR) of voltage divider, the Wheatstone bridge is used to interface with that sensor. This project will focus on designing an integrated readout interfacing circuit (ROIC) for resistive-based sensing. The circuit design acts as conditioning circuit for easy interface with microcontroller. The topology of the op-amp was studied in order to have an operational amplifier with high gain 8. The circuit design acts as conditioning circuit for easy interface with microcontroller. It is used to extract the resistive changes of sensor and convert it to the voltage value. Besides that, two types of Wheatstone bridge are comparing in term of sensitivity of the circuit. The bridge circuits that give highest sensitivity will be used as sub-circuit of the ROIC. 2. Methodology and Design Architecture The conventional Wheatstone bridge is widely used as its technique offers an attractive alternative for measuring small resistance. Fig. 1 (a) shows the used bridge configuration suitable for sensor applications, which relate the bridge resistance values to the bridge output voltage. The design is used to convert the variation resistance value of the sensors into a voltage value. In this configuration, IN is the excitation voltage, R1, R2 and R4 is the value of the fixed bridge resistor and the variable resistor, R3, where the element varying bridge produces the change in voltage output. Major problem encountered in the bridge circuit is low sensitivity due to the large excitation voltage for sufficient full-scale output voltage. This leads in power dissipation and the possibility of error due to sensor self-heating. Therefore, ROIC based on the Wheatstone bridge with modification using operational amplifier to increase the sensitivity of the conventional bridge circuit has been proposed. Fig. 1 (b) shows the architecture of an active bridge. A buffer is employed in the arm AB to provide isolation from the adjacent arm AD and also to make the circuit more sensitive.
(a)
(b)
Fig. 1 (a). The conventional Wheatstone bridge; (b). Active bridge
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Nur Izzati Mohd Fauzi et al. / Procedia Computer Science 76 (2015) 430 – 435
(a)
(b)
Fig. 2. (a) Telescopic Op-amp architecture, (b) Two stage Op-amp architecture
Fig. 2 (a) shows the architecture of telescopic op-amp. This topology produce high power efficiency due to its load compensation and also give high gain compare to other topologies of op-amp9. Fig. 2 (b) shows the architecture of the chosen op-amp. The operational amplifier comprises of two stages which are input stage and gain stage. Two stage operational amplifiers is one of the most widely used CMOS amplifiers until today. The first stage of an op-amp is a differential amplifier which converts the input voltage to current. Design for both op-amp consists of determining the specifications, selecting device sizes and biasing conditions. For this project, the op-amp architecture has been design based on single supply op-amp10. The sizing parameters of each MOSFET in the op-amp were calculated using Id equations and based on the specifications of the op-amp such as open-loop gain, current, output voltage swing and ICMR.
(a)
(b)
Fig. 3. (a) Conventional Bridge Circuit; (b) Schematic of proposed ROIC
Fig. 3 (a) shows the construction of the conventional Wheatstone bridge circuit with the combination of an inverting adder. For simulation purpose, a resistive-based sensor is replaced by ideal resistor which represent by R2. All resistance value were set based on nominal value of resistive-based sensor 10k ohm2. The simulation of conventional Wheatstone bridge is compared with simulation of active bridge circuit as shown in Fig. 3 (b). The circuit consists of an active bridge circuit that employs buffer op-amp. Only one element varying bridge configuration is used, which is one sensor is connected across the one of four arms of the bridge. The sensor is placed on the adjacent sides of the bridge. For simulation purpose, the sensor will replace by ideal resistor and varies from minimum value, 10 ohm to nominal value of resistive-based sensor which is 10k ohm. This nominal value is based on the FSR pressure sensor. This ROIC is designed in such a way to increase the sensitivity of the conventional bridge circuit in measuring incremental resistance change of resistive sensor, where variation in resistive value due to physical quantity is very small.
Nur Izzati Mohd Fauzi et al. / Procedia Computer Science 76 (2015) 430 – 435
3. Results and Discussion 3.1. Op-Amp Simulation
(b)
(a)
Fig. 4. (a) Open-Loop Frequency Response result for Telescopic and Two Stage Op-Amp in Magnitude (dB), (b) Open-Loop Frequency Response result for Telescopic and Two Stage Op-amp in Phase (°)
The functionality of op-amp, open-loop frequency response, offset voltage, and ICMR were analysed based on the desired specifications. Both Fig. 4 (a) and (b) shows the simulation of open-loop frequency response for telescopic and two stage amplifier. The gain obtained from the telescopic graph is approximate to 16dB. This value will be compare based on the simulation of open-loop frequency response for two stage op-amp. From the two stage graph, the obtained open-loop gain is around 78dB. Higher gain will increase the sensitivity of the ROIC circuit. The gain of the op-amp can be increased depend on the load capacitance. However, it will affect the stability of the op-amp and stable gain cannot be obtained. The gain margin and phase margin obtained from the simulation are approximately 27dB and 90 o respectively. Table 1 show the comparison of DC gain for two stage and telescopic amplifier. The result shows that the two stage op-amp has higher DC gain. Since the DC gain of two stage op-amp is higher than telescopic amplifier, this two stage op-amp is used in ROIC design. Table 1. Comparison of DC Gain for Telescopic Amplifier and Two Stage Type of Operational Amplifier
DC Gain (dB)
Telescopic
16
Two Stage
78
(a)
(b)
Fig. 5. (a) Offset Voltage Test Setup, (b) Offset voltage simulation result
Fig. 5. (a) shows the test setup for finding offset voltage and output voltage swing. A positive input terminal of op-amp is connected to the DC voltage that swept from -1 to 2.5V during simulation. While the
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negative terminal is connected to the output of op-amp that act as feedback for the setup. The input offset voltage is defined as the voltage that must be applied between the two input terminals of the op-amp to obtain zero volts at the output. Based on simulation in Fig. 5 (b), it shows that the offset voltage of the two stage amplifier circuit is 0V and the output voltage swing is from 0V to 2.5V.
Fig. 6. Input Common Mode Range
From the graph in Fig. 6, the obtained ICMR for this op-amp is between 0.66V and 1.50V. If more than 1.50V or lower than 0.66V, the current will unstable. The simulation results obtained for two stage op-amp are tabulated in Table 2. Table 2. Simulated Two Stage Op-Amp Specifications. Open-Loop gain
Vin (offset)
Vout (swing)
ICMR
78dB
0V
0V to 2.5V
0.66V to 1.50V
3.2. ROIC Analysis
(a)
(b)
Fig. 7. (a) Simulation Result for Different Topology of Op-amp; (b) Simulation for Different type of Bridge Circuit
Fig. 7 (a) shows the simulation result for telescopic and two stage op-amp. The sensitivity of the circuit for both topologies is tabulated in Table V. It is shows that the higher gain of op-amp will increase the sensitivity of the circuit to produce significant output voltage. Fig.7 (b) shows the simulation result of full bridge conventional circuit (blue line) and proposed active bridge circuit (green line). From the simulation result (Vout vs. resistance), the sensitivity of the circuit is defined. The sensitivity of the signal conditioning circuit was defined as the percentage change in output voltage of the circuit to the resistance change of the sensor. We can see that, the slope of the active bridge is much greater then Wheatstone bridge circuit. Meaning that, the sensitivity of active bridge circuit is higher than Wheatstone bridge.
Nur Izzati Mohd Fauzi et al. / Procedia Computer Science 76 (2015) 430 – 435 Table 3. Sensitivity Based On Two Different Bridge Circuit Type of bridge
% Sensitivity (mV/Ω)
Conventional bridge
0.09
Proposed active bridge (ROIC)
4.33
Based on Table 3, shows the sensitivity of proposed active bridge is higher than conventional bridge. This is due to modification of Wheatstone’s bridge by using active components. 4. Conclusion An integrated readout circuit using active bridge was designed using SILTERRA CL130G technology (0.13 CMOS Logic Generic). The results obtained show that the sensitivity of proposed active bridge circuit improves by 4% compared to the conventional bridge. This is due to modification of Wheatstone’s bridge by using active components, which is the custom designed two stage Operational Amplifier with 78dB open-loop gain. The sensitivity improvement would allow any resistive-based sensors to be integrated with ROIC to produce more significant output voltage of shifted resistance. 5. Acknowledgment This work is partially supported by Niche Research Grant Scheme (NRGS) under file number 600RMI/NRGS 5/3 (7/2013) from the Ministry of Education (MOE) Malaysia. 6. References 1.
K. Weiß and H. Wörn. The Working Principle of Resistive Tactile Sensor Cells. In Proceedings of the IEEE International Conference on Mechatronics & Automation Niagara Falls. Canada. 2005. pp. 471–476. 2. T. Islam, F. A. Siddiqui, S. A. Khan, and S. S. Islam. A Sensitive Detection Electronics for Resistive Sensor. In 3rd International Conference on Sensing Technology, Nov. 30 – Dec. 3. Tainan, Taiwan. 2008. pp. 259–264. 3. Alejandro Duran Carrillo de Abornoz, Diego Ramirez Munoz, Jaime Sanchez Moreno, Silvia Casans Berga, Edith Navarro Anton. A New Gas Sensor Electronic Interface with Generalized Impedance Converter. Sensors and Actuators B 134. 2008. pp. 591-596. 4. R. Pallas-Areney, J.G. Webster, Sensor and Signal Conditioning, 2nd ed., John Wiley & Sons, Boston, 2001, p.634. 5. G. Ferri, P. De Laurentiis, I. Elettrica, F. Ingegneria, and U. L. Aquila. A low-voltage Cmos phase shifter as a resistive sensor transducer. In Circuits and Systems. Proc. ISCAS 2000. The 2000 IEEE International Symposium. Geneva. vol. 2. 2000. pp. 605–608. 6. A. De Marcellis, C. Reig, and M.-D. Cubells. A novel current-based approach for very low variation detection of resistive sensors in wheatstone bridge configuration. IEEE SENSORS 2014 Proc. Nov 2014. pp. 2104–2106. 7. J. V Rethy, H. Danneels, V. J. D. Smedt, W. Dehaene, G. Gielen. An Energy-Efficient BBPLL-based ForceBlanaced Wheatstone Bridge Sensor-to-Digital Interface in 130nm CMOC. IEEE Asian Solid-State Circuits Conference. November 2012. pp. 12-14. 8. M. H. Hamzah, A. B. Jambek and U. Hashim. Design Analysis of a Two-stage CMOS Op-amp using Silterra’s 0.13 um Technology. IEEE Synmposium on Computer Applications & Industrial Electronics (ISCAIE). Penang, Malaysia. April 2014. pp. 7-8. 9. A. F. Yeknami, F. Qazi, J. J. Dabrowski and A. Alvandpour, “Design of OTAs for Ultra-Low-Power Sigma-delta ADCs in Medical Applications”, International Conference on Signals and Electronic Systems, 2010, 229-232,. 10. R. Jacob Baker, D. R. “Operational Amplifier II” in CMOS Circuit Design, Layout, and Simulation, 2 nd ed. IEEE Press Series on Microelectronic Systems, 2005.
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ScienceDirect Procedia Computer Science 76 (2015) 430 – 435
2015 IEEE International Symposium on Robotics and Intelligent Sensors (IRIS 2015)
Integrated Readout Circuit Using Active Bridge For Resistivebased Sensing Nur Izzati Mohd Fauzi, Nur Farahin Anuar, Sukreen Hana Herman, Wan Fazlida Hanim Abdullah* Faculty of Electrical Engineering, Universiti Teknologi Mara , 40450 Shah Alam, Selangor
Abstract An integrated Readout Interfacing Circuit (ROIC) for resistive-based sensors using SILTERRA CMOS 0.13 μm technology that reads resistance shift and converts it to voltage was designed. In conventional practice, resistive-based sensors are interfaced with Wheatstone bridge to transform the sensor signal to voltage. Due to low sensitivity of Wheatstone bridge, the output voltage of shifted resistance is not significant. The objective of this project is to propose an integrated interfacing circuit using Wheatstone bridge with improved sensitivity. The project scope focuses on integrated circuit design of readout circuitry for resistive-based sensors. An active bridge, a modification of standard Wheatstone bridge using active components was used as ROIC. The sensitivity of the circuit is defined as percentage change in output voltage of the circuit to the changes in resistance of the sensor. Results show that, the active bridge circuit is almost four times more sensitive compare to conventional bridge circuit. The sensitivity improvement would allow any resistive-based sensors to be integrated with ROIC to produce more significant output voltage of shifted resistance. Keywords:Integrated Circuit, Readout Interfacing Circuit; Resistive-based Sensor; Sensitivity
1. Introduction Nowadays, robotics tactile sensor systems become more important, due to the demand for collision safety and reactive control in unstructured environments. Based on readings, there are three major classes that can measure principle of the tactile sensor cells which are optical, capacitive and resistive effects 1. Resistive are some of the common sensor because of relatively inexpensive to manufacture and easy to
* Corresponding author. Tel.: +60 19-2217347. E-mail address:[email protected]
1877-0509 © 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of the 2015 IEEE International Symposium on Robotics and Intelligent Sensors (IRIS 2015) doi:10.1016/j.procs.2015.12.284
Nur Izzati Mohd Fauzi et al. / Procedia Computer Science 76 (2015) 430 – 435
interface with signal conditioning circuit2. A resistive-based sensor is a category of sensors that acquire information through physical or environmental change. The measured characteristics can be properties such as temperature, vibration, shape, and normal forces. Tactile sensor may also measure one or more of these properties. Read-out Interfacing Circuit (ROIC) refers to the integrated circuit that is specifically used reading detectors of a sensitivity that is very low. Discrete circuit may not be useful as noise may be large enough to cover up whole signal. Voltage dividers and Wheatstone Bridge followed by differential or instrumentation amplifier are common conditioning circuit for resistive sensor in which an output signal is obtained3,4. Therefore, a voltage-mode Wheatstone bridge (VMWB) is employed for firstly interfacing resistive sensors in analog system. It is used to compare the signal to some set point value. The conventional Wheatstone bridge as the main topologies for resistive sensors offers an attractive for measuring small resistance and widely used in2,5. A. De Marcellis et al6, present a new approach based on current signals, suitable for the detection of very low variations of resistive sensors in a Wheatstone bridge configuration. One of the paper shows discussion on the force-balance Wheatstone bridge when interface with resistive-based sensor7. The project scope of this paper is comparing the sensitivity of balance Wheatstone bridge with voltage divider that to be used as conditioning circuit for resistive sensor. Due to low power supply rejection ratio (PSRR) of voltage divider, the Wheatstone bridge is used to interface with that sensor. This project will focus on designing an integrated readout interfacing circuit (ROIC) for resistive-based sensing. The circuit design acts as conditioning circuit for easy interface with microcontroller. The topology of the op-amp was studied in order to have an operational amplifier with high gain 8. The circuit design acts as conditioning circuit for easy interface with microcontroller. It is used to extract the resistive changes of sensor and convert it to the voltage value. Besides that, two types of Wheatstone bridge are comparing in term of sensitivity of the circuit. The bridge circuits that give highest sensitivity will be used as sub-circuit of the ROIC. 2. Methodology and Design Architecture The conventional Wheatstone bridge is widely used as its technique offers an attractive alternative for measuring small resistance. Fig. 1 (a) shows the used bridge configuration suitable for sensor applications, which relate the bridge resistance values to the bridge output voltage. The design is used to convert the variation resistance value of the sensors into a voltage value. In this configuration, IN is the excitation voltage, R1, R2 and R4 is the value of the fixed bridge resistor and the variable resistor, R3, where the element varying bridge produces the change in voltage output. Major problem encountered in the bridge circuit is low sensitivity due to the large excitation voltage for sufficient full-scale output voltage. This leads in power dissipation and the possibility of error due to sensor self-heating. Therefore, ROIC based on the Wheatstone bridge with modification using operational amplifier to increase the sensitivity of the conventional bridge circuit has been proposed. Fig. 1 (b) shows the architecture of an active bridge. A buffer is employed in the arm AB to provide isolation from the adjacent arm AD and also to make the circuit more sensitive.
(a)
(b)
Fig. 1 (a). The conventional Wheatstone bridge; (b). Active bridge
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Nur Izzati Mohd Fauzi et al. / Procedia Computer Science 76 (2015) 430 – 435
(a)
(b)
Fig. 2. (a) Telescopic Op-amp architecture, (b) Two stage Op-amp architecture
Fig. 2 (a) shows the architecture of telescopic op-amp. This topology produce high power efficiency due to its load compensation and also give high gain compare to other topologies of op-amp9. Fig. 2 (b) shows the architecture of the chosen op-amp. The operational amplifier comprises of two stages which are input stage and gain stage. Two stage operational amplifiers is one of the most widely used CMOS amplifiers until today. The first stage of an op-amp is a differential amplifier which converts the input voltage to current. Design for both op-amp consists of determining the specifications, selecting device sizes and biasing conditions. For this project, the op-amp architecture has been design based on single supply op-amp10. The sizing parameters of each MOSFET in the op-amp were calculated using Id equations and based on the specifications of the op-amp such as open-loop gain, current, output voltage swing and ICMR.
(a)
(b)
Fig. 3. (a) Conventional Bridge Circuit; (b) Schematic of proposed ROIC
Fig. 3 (a) shows the construction of the conventional Wheatstone bridge circuit with the combination of an inverting adder. For simulation purpose, a resistive-based sensor is replaced by ideal resistor which represent by R2. All resistance value were set based on nominal value of resistive-based sensor 10k ohm2. The simulation of conventional Wheatstone bridge is compared with simulation of active bridge circuit as shown in Fig. 3 (b). The circuit consists of an active bridge circuit that employs buffer op-amp. Only one element varying bridge configuration is used, which is one sensor is connected across the one of four arms of the bridge. The sensor is placed on the adjacent sides of the bridge. For simulation purpose, the sensor will replace by ideal resistor and varies from minimum value, 10 ohm to nominal value of resistive-based sensor which is 10k ohm. This nominal value is based on the FSR pressure sensor. This ROIC is designed in such a way to increase the sensitivity of the conventional bridge circuit in measuring incremental resistance change of resistive sensor, where variation in resistive value due to physical quantity is very small.
Nur Izzati Mohd Fauzi et al. / Procedia Computer Science 76 (2015) 430 – 435
3. Results and Discussion 3.1. Op-Amp Simulation
(b)
(a)
Fig. 4. (a) Open-Loop Frequency Response result for Telescopic and Two Stage Op-Amp in Magnitude (dB), (b) Open-Loop Frequency Response result for Telescopic and Two Stage Op-amp in Phase (°)
The functionality of op-amp, open-loop frequency response, offset voltage, and ICMR were analysed based on the desired specifications. Both Fig. 4 (a) and (b) shows the simulation of open-loop frequency response for telescopic and two stage amplifier. The gain obtained from the telescopic graph is approximate to 16dB. This value will be compare based on the simulation of open-loop frequency response for two stage op-amp. From the two stage graph, the obtained open-loop gain is around 78dB. Higher gain will increase the sensitivity of the ROIC circuit. The gain of the op-amp can be increased depend on the load capacitance. However, it will affect the stability of the op-amp and stable gain cannot be obtained. The gain margin and phase margin obtained from the simulation are approximately 27dB and 90 o respectively. Table 1 show the comparison of DC gain for two stage and telescopic amplifier. The result shows that the two stage op-amp has higher DC gain. Since the DC gain of two stage op-amp is higher than telescopic amplifier, this two stage op-amp is used in ROIC design. Table 1. Comparison of DC Gain for Telescopic Amplifier and Two Stage Type of Operational Amplifier
DC Gain (dB)
Telescopic
16
Two Stage
78
(a)
(b)
Fig. 5. (a) Offset Voltage Test Setup, (b) Offset voltage simulation result
Fig. 5. (a) shows the test setup for finding offset voltage and output voltage swing. A positive input terminal of op-amp is connected to the DC voltage that swept from -1 to 2.5V during simulation. While the
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Nur Izzati Mohd Fauzi et al. / Procedia Computer Science 76 (2015) 430 – 435
negative terminal is connected to the output of op-amp that act as feedback for the setup. The input offset voltage is defined as the voltage that must be applied between the two input terminals of the op-amp to obtain zero volts at the output. Based on simulation in Fig. 5 (b), it shows that the offset voltage of the two stage amplifier circuit is 0V and the output voltage swing is from 0V to 2.5V.
Fig. 6. Input Common Mode Range
From the graph in Fig. 6, the obtained ICMR for this op-amp is between 0.66V and 1.50V. If more than 1.50V or lower than 0.66V, the current will unstable. The simulation results obtained for two stage op-amp are tabulated in Table 2. Table 2. Simulated Two Stage Op-Amp Specifications. Open-Loop gain
Vin (offset)
Vout (swing)
ICMR
78dB
0V
0V to 2.5V
0.66V to 1.50V
3.2. ROIC Analysis
(a)
(b)
Fig. 7. (a) Simulation Result for Different Topology of Op-amp; (b) Simulation for Different type of Bridge Circuit
Fig. 7 (a) shows the simulation result for telescopic and two stage op-amp. The sensitivity of the circuit for both topologies is tabulated in Table V. It is shows that the higher gain of op-amp will increase the sensitivity of the circuit to produce significant output voltage. Fig.7 (b) shows the simulation result of full bridge conventional circuit (blue line) and proposed active bridge circuit (green line). From the simulation result (Vout vs. resistance), the sensitivity of the circuit is defined. The sensitivity of the signal conditioning circuit was defined as the percentage change in output voltage of the circuit to the resistance change of the sensor. We can see that, the slope of the active bridge is much greater then Wheatstone bridge circuit. Meaning that, the sensitivity of active bridge circuit is higher than Wheatstone bridge.
Nur Izzati Mohd Fauzi et al. / Procedia Computer Science 76 (2015) 430 – 435 Table 3. Sensitivity Based On Two Different Bridge Circuit Type of bridge
% Sensitivity (mV/Ω)
Conventional bridge
0.09
Proposed active bridge (ROIC)
4.33
Based on Table 3, shows the sensitivity of proposed active bridge is higher than conventional bridge. This is due to modification of Wheatstone’s bridge by using active components. 4. Conclusion An integrated readout circuit using active bridge was designed using SILTERRA CL130G technology (0.13 CMOS Logic Generic). The results obtained show that the sensitivity of proposed active bridge circuit improves by 4% compared to the conventional bridge. This is due to modification of Wheatstone’s bridge by using active components, which is the custom designed two stage Operational Amplifier with 78dB open-loop gain. The sensitivity improvement would allow any resistive-based sensors to be integrated with ROIC to produce more significant output voltage of shifted resistance. 5. Acknowledgment This work is partially supported by Niche Research Grant Scheme (NRGS) under file number 600RMI/NRGS 5/3 (7/2013) from the Ministry of Education (MOE) Malaysia. 6. References 1.
K. Weiß and H. Wörn. The Working Principle of Resistive Tactile Sensor Cells. In Proceedings of the IEEE International Conference on Mechatronics & Automation Niagara Falls. Canada. 2005. pp. 471–476. 2. T. Islam, F. A. Siddiqui, S. A. Khan, and S. S. Islam. A Sensitive Detection Electronics for Resistive Sensor. In 3rd International Conference on Sensing Technology, Nov. 30 – Dec. 3. Tainan, Taiwan. 2008. pp. 259–264. 3. Alejandro Duran Carrillo de Abornoz, Diego Ramirez Munoz, Jaime Sanchez Moreno, Silvia Casans Berga, Edith Navarro Anton. A New Gas Sensor Electronic Interface with Generalized Impedance Converter. Sensors and Actuators B 134. 2008. pp. 591-596. 4. R. Pallas-Areney, J.G. Webster, Sensor and Signal Conditioning, 2nd ed., John Wiley & Sons, Boston, 2001, p.634. 5. G. Ferri, P. De Laurentiis, I. Elettrica, F. Ingegneria, and U. L. Aquila. A low-voltage Cmos phase shifter as a resistive sensor transducer. In Circuits and Systems. Proc. ISCAS 2000. The 2000 IEEE International Symposium. Geneva. vol. 2. 2000. pp. 605–608. 6. A. De Marcellis, C. Reig, and M.-D. Cubells. A novel current-based approach for very low variation detection of resistive sensors in wheatstone bridge configuration. IEEE SENSORS 2014 Proc. Nov 2014. pp. 2104–2106. 7. J. V Rethy, H. Danneels, V. J. D. Smedt, W. Dehaene, G. Gielen. An Energy-Efficient BBPLL-based ForceBlanaced Wheatstone Bridge Sensor-to-Digital Interface in 130nm CMOC. IEEE Asian Solid-State Circuits Conference. November 2012. pp. 12-14. 8. M. H. Hamzah, A. B. Jambek and U. Hashim. Design Analysis of a Two-stage CMOS Op-amp using Silterra’s 0.13 um Technology. IEEE Synmposium on Computer Applications & Industrial Electronics (ISCAIE). Penang, Malaysia. April 2014. pp. 7-8. 9. A. F. Yeknami, F. Qazi, J. J. Dabrowski and A. Alvandpour, “Design of OTAs for Ultra-Low-Power Sigma-delta ADCs in Medical Applications”, International Conference on Signals and Electronic Systems, 2010, 229-232,. 10. R. Jacob Baker, D. R. “Operational Amplifier II” in CMOS Circuit Design, Layout, and Simulation, 2 nd ed. IEEE Press Series on Microelectronic Systems, 2005.
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