Int. Journal of Electrical & Electronics Engg.
Vol. 2, Spl. Issue 1 (2015)
e-ISSN: 1694-2310 | p-ISSN: 1694-2426
High Gain, Low Noise Instrumentation Amplifier Using Three Operational Amplifiers for Weak Biomedical Signal 1
Amit Kumar Chidar, 2Pramod Kumar Jain, 3D.S Ajnar
1,2,3
Microelectronics and VLSI Design, E&I Department, S.G.S.I.T.S Indore, M.P, India
1
amitchidar08@gmail.com, 2prjain@sgsits.ac.in, 3ajnards@gmail.com
Abstract:- This paper investigate the performance of Instrumentation amplifier (INA) using three operational Amplifier. The proposed circuit works for low input voltage equalised to the heart beat of the human being to analyses the ECG (Biomedical application) response. The analyses of Gain, Bandwidth, Unity GBW, Phase margin and output noise for operational amplifier used in INA and For the INA Gain, Bandwidth, output noise and power Dissipation are analysed. The proposed circuit designed on UMC 180nm CMOS technology file and all the simulation done on CADENCE SPECTRE Simulator. Keyword: Amplifier basics, Differential Amplifier using MOSFET, Operational Amplifier, Instrumentation Amplifier, ECG (Biomedical application), Analog Electronics.
I. INTRODUCTION Today Biomedical Application play a vital role in the field of Technology but, it is very challenging task to fetch the biomedical signal because of very small amplitude and frequency of few hertz. As the biomedical signal is very small and equal to noise if it is difficult task to find it’s presence. Like Heart Beat signal or Pulse Signal which are very weak in nature [1, 2]. So, to overcome from this problem we need proper amplification, modified Gain, Higher Bandwidth and suppressed noise device like, Instrumentation Amplifier. An instrumentation amplifier is the one of the most effective block of Biomedical field mainly used in some application such as ECG, Transducer or sensor based biomedical devices, Microelectronics Devices etc. It provides better amplification, good linearity, Gain, Bandwidth and having properties of suppressing noise from the weak biomedical signal. Basically it constitute of two differential input and single ended output. The basic building block of biomedical device is shown below in the Fig.1
output pulse after analysing Bio-medical signal. The Biomedical device such as ECG having quite similar blocks shown in the Fig. 1 and Instrumentation Amplifier play an important role in it. In this paper, SECTION II and SECTION III describe the operational amplifier and the proposed instrumentation amplifier respectively. SECTION IV and SECTION V describe the simulation results and conclusion respectively. II. DESCRIPTION OF OPERATIONAL AMPLIFIER FOR DESIGNING OF INA The basic building block of proposed circuit is an Operational amplifier. There are three operational amplifiers used in the proposed INA. Each operational amplifier is dual stage amplifier basically used to enhance the gain of the INA. The schematic of operational amplifier shown below in the Fig. 2.
Fig.2 Operational Amplifier for the Proposed INA
The operational amplifier consist [5] of two stages first stage is gain stage and second stage is called output stage. Basically, second stage enhances the gain and provides frequency compensation through compensation capacitance Cc. The nmos MOS transistor M1, M2 act as the differential stage, pmos transistor M3,M4 act as current mirror, M5, M6 and M8 are used for biasing. The output is taken out from the output load capacitance, the relationship between load capacitance CL and compensation capacitance CC are shown below:CL ≥ 2.2Cc........................(1) Aspect ratio i.e. (W/L ratio) of MOS transistor for the operational amplifier shown below in the TABLE I:-
Fig. 1 Biomedical Signal Fetching and Detecting Device
The Amplifier used in the device shown above is an Instrumentation Amplifier working over the Biomedical signal, the Amplifier shows good CMRR, Gain, BW, Low power dissipation [3] and Low noise. The Device shown above with Instrumentation Amplifier provided digital 33
Aspect ratio W/L (µm/ µm)
M1, M2 3/.5
M3, M4 7/.5
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TABLE I M5, M6 12/1
M7
M8
87/.5
75/1
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Int. Journal of Electrical & Electronics Engg.
Vol. 2, Spl. Issue 1 (2015)
e-ISSN: 1694-2310 | p-ISSN: 1694-2426
III. PROPOSED INSTRUMENTATION AMPLIFIER The proposed Instrumentation Amplifier consist of three operational amplifier and six resistor to carry out maximum gain [6]. The schematic of proposed circuit shown below in the Fig.3
Fig.6 Phase Margin and Unity GBW
Fig. 3 Proposed Instrumentation Amplifier (INA)
The proposed circuit are basically used to amplifying small or weak signals of few volts i.e. (0.5mv-4mv) range at some common mode voltage range [4]. The output and differential input voltage relationship for INA are shown below:) ∗ ((1 + 2 ) ).............(2) = −( −
The resistances of the proposed circuit can be designed through the nmos transistor by which the chip area can be reduced. IV. SIMULATION RESULTS The proposed circuit is designed on UMC 180nm CMOS technology file using cadence tool. All the simulated results related to Operational Amplifier and Proposed INA is obtained by SPECTRE SIMULATOR tool. The simulated results for Operational Amplifier are shown below from Fig. 4 to Fig. 6.
The related results for Operational Amplifier are shown in the TABLE II. PARAMETERS
TABLE II Results for Operational Amplifier Result Obtained
Technology
180 nm
Supply voltage
1.8 v
Gain
67.083 dB
3-dB Bandwidth
11.496 KHz
Unity GBW
25.2678 MHz
Phase Margin
63.858 deg
B. Simulated Results for Proposed Instrumentation Amplifier (INA) All the Simulation results for proposed INA i.e. Gain, 3-dB Bandwidth and output referred noise are shown below in the Fig. 7, Fig. 8 and Fig. 9 respectively. All results are obtained by using SPECTRE SIMULATOR tool.
Fig.7 Gain of proposed INA
Fig. 4 Operational Amplifier Gain
Fig.8 3-dB Bandwidth of Proposed INA
Fig.5 3-dB Bandwidth of Operational Amplifier
Fig.5 3-dB Bandwidth of Operational Amplifier
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Fig.9 Output Referred Noise (V/sqrt(Hz)) The related results for INA are shown below in the TABLE III.
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Int. Journal of Electrical & Electronics Engg. TABLE III Results for Proposed Instrumentation Amplifier PARAMETER This [4] [6] work Technology (um) 0.18 0.18 0.5 Supply voltage 1.8v N/A N/A Gain (dB) 42.330 19.6 19.9 Bandwidth 135.91 N/A N/A KHz Output noise 3.05µ N/A N/A (V**2/(Hz)) Power dissipation 0.792m N/A N/A W
Vol. 2, Spl. Issue 1 (2015)
e-ISSN: 1694-2310 | p-ISSN: 1694-2426
[7] 0.8 N/A 40 N/A N/A 122u
V. CONCLUSION The proposed Instrumentation Amplifier basically used for amplifying the small amplitude and low frequency signal equalized to heart beat or pulse. The designed circuit shows high gain, low power dissipation and smaller area wise. The supply voltage of 1.8 volts required for the circuit. All the simulation results are clearly obtained by the help of cadence spectre simulator. REFERENCES Chien-Jung Chou; Bing-Jye Kuo; Li Guang Chen, Po-Yun Hsiao and Tsung-Hsien Lin, “A 1-V low noise readout front end for biomedical applications in 0.18μm CMOS,” In Proc. Int. Symp. VLSI-DAT., Hsin Chu, pp. 295-298, Apr 2010. Yazicioglu,R.F.; Merken,P and Van Hoof, C.,“ Integrated low power 24channel EEG front end” Electronic Letter, vol. 41 no. 8, pp 457-458,Apr 2005. Shojaei-Baghini, M.; Lal, R.K.; and Sharma, D.K., “An ultra low power instrumentation amplifier for biomedical application,”Int.Workshop IEEE (B.C.S) Dec 2004, pp 691-699 April 2004. Yasin,F.M.; Yap,M.T.;and Reaz,M.B.I ,“CMOS Instru-mentation Amplifier with Offset Cancellation Circuitry for Biomedical Applications,” In Proc. of 5th WSEAS, Spain, pp 168-171, 2006. Philip E. Allen and Douglas R.Holberg, CMOS Analog Circuit Design, Oxford University Press, pp 180-196, March 2002. Chih-Jen Yen ; Wen-Yaw Chung and Mely Chen Chi ,“Micro-Power Low Offset Instrumentation Amplifier IC Design For BioMedical System Applications”,IEEE Transactions On Circuits And Systems-I:Regular Papers ,Vol.51,No.4, pp 691-699 April 2004. Ananth, R.S. and Lee, E.K., “Design of a low power implantable electromyogram amplifier,” In Proc.IEEE Inter.Symp.on Circuits and Systems (ISCAS’04), vol 4, pp. 9-12, 2004.
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