A Test Methodology to Measure the Open-Loop Voltage Gain of an Operational Amplifier

Authors: Maninder Kaur Gill, Alpana Agarwal

Abstract:

It is practically not feasible to measure the open-loop voltage gain of the operational amplifier in the open loop configuration. It is because the open-loop voltage gain of the operational amplifier is very large. In order to avoid the saturation of the output voltage, a very small input should be given to operational amplifier which is not possible to be measured practically by a digital multimeter. A test circuit for measurement of open loop voltage gain of an operational amplifier has been proposed and verified using simulation tools as well as by experimental methods on breadboard. The main advantage of this test circuit is that it is simple, fast, accurate, cost effective, and easy to handle even on a breadboard. The test circuit requires only the device under test (DUT) along with resistors. This circuit has been tested for measurement of open loop voltage gain for different operational amplifiers. The underlying goal is to design testable circuits for various analog devices that are simple to realize in VLSI systems, giving accurate results and without changing the characteristics of the original system. The DUTs used are LM741CN and UA741CP. For LM741CN, the simulated gain and experimentally measured gain (average) are calculated as 89.71 dB and 87.71 dB, respectively. For UA741CP, the simulated gain and experimentally measured gain (average) are calculated as 101.15 dB and 105.15 dB, respectively. These values are found to be close to the datasheet values.

Keywords: Device under test, open-loop voltage gain, operational amplifier, test circuit.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1339966

References:

[1] W. M. C. Sansen, M. Steyaert, and P. J. V. Vandeloo, “Measurement of operational amplifier characteristics in the frequency domain,” IEEE Trans. Instrum. Meas., vol. IM-34, pp. 59–64, Feb. 1985.
[2] K. Higuchi and H. Shintani, “New measurement methods of dominant pole- type operational amplifier parameters,” IEEE Trans. Ind. Electron., vol. IE-34, pp. 357–365, June 1987.
[3] S. S. Awad, “A simple method to estimate the ratio of the second pole to the gain-bandwidth product of matched operational amplifiers,” IEEE Trans. Instrum. Meas., vol. 39, pp. 429–432, Apr. 1990.
[4] S. Natarajan, “A simple method to estimate gain-bandwidth product and the second pole of the operational amplifiers,” IEEE Trans. Instrum. Meas., vol. 40, pp. 43–45, Feb. 1991.
[5] S. Porta and A. Carlosena, “On the experimental methods to characterize the opamp response: A critical view,” IEEE Trans. Instrum. Meas., vol. 43, pp. 245–249, Apr. 1996.
[6] G. Di Cataldo. G. Paltnisano. G. Palumbo and S. Pennisi, “High-speed voltage buffers for the experimental characterization of CMOS transconductance operational amplifiers”, IEEE Trans. Instrum. and Meas. vol.48, no. l, pp. 31-33, 1999.
[7] R. Pintelon and J. Schoukens, "Measurement and modeling of linear systems in the presence of non-linear distortions," Mechanical System and SignaI Processing, vol. 16. no.5.p~. 785-801,2002.
[8] R. Pintelon, J. Schoukens, W. Van Moer and Y. Rolain, "Identification of linear systems in the presence of nonlinear distortions:' IEEE Trans. Instrum. and Meas., vol. 50. no. 4, pp. 855-863.2001.
[9] G. Giustolisi and G. Palumbo, “An approach to test open-loop parameters of feedback amplifiers,” IEEE Trans. Circuits Syst. I, vol. 49, pp. 70–75, Jan. 2002.
[10] R. Pallás-Areny and J. G.Webster, “Common mode rejection ratio in differential amplifiers,” IEEE Trans. Instrum. Meas., vol. 40, pp. 669–676, June 1991.
[11] M. E. Brinson and D. J. Faulkner, “New approaches to measurement of operational amplifier common-mode rejection ratio in the frequency domain,” Proc. Inst. Elect. Eng. Circuits Devices Syst., vol. 142, no. 4, pp. 247–253, 1995.
[12] G. Giustolisi, G. Palmisano, and G. Palumbo, “CMRR frequency response of CMOS operational transconductance amplifiers,” IEEE Trans. Instrum. Meas., vol. 49, pp. 137–143, Feb. 2000.
[13] M. S. J. Steyaert and W. M. C. Sansen, “Power supply rejection ratio in operational transconductance amplifiers,” IEEE Trans. Circuits Syst., vol. 37, pp. 1077–1084, Oct. 1990.
[14] M. E. Brinson and D. J. Faulkner, “Measurement and modeling of operational amplifier power supply rejection,” Int. J. Electron., vol. 78, no.4, pp. 667–678, 1995.
[15] Pintelon R., Vandersteen G., Ludwig De Locht, Rolain Y, Schoukens J., "Experimental characterization of operational amplifiers: a system identification Approach-part I&II: theory and simulations”, Instrumentation and Measurement, IEEE Transactions on, on page(s): 854 - 876 Volume: 53, Issue: 3, June 2004.
[16] James M Bryant, “Simple Op Amp Measurements”, Analog Dialogue, Vol. 45- April 2011.
[17] Pintelon, R. Vandersteen, G. Rolain, Y. "Experimental characterization of operational amplifiers: A system identification approach", Instrumentation and Measurement Technology Conference, 2003. IMTC '03. Proceedings of the 20th IEEE, On page(s): 362 - 367 Volume: 1, 20-22 May 2003.