AN-24| Application Note
A Simplified Test Set for Op Amp Characterization
A Simplified Test Set for Op Amp Characterization
INTRODUCTION The test set described in this paper allows complete quantitative characterization of all dc operational amplifier parameters quickly and with a minimum of additional equipment The method used is accurate and is equally suitable for laboratory or production test for quantitative readout or for limit testing As embodied here the test set is conditioned for testing the LM709 and LM101 amplifiers however simple changes discussed in the text will allow testing of any of the generally available operational amplifiers Amplifier parameters are tested over the full range of common mode and power supply voltages with either of two output loads Test set sensitivity and stability are adequate for testing all presently available integrated amplifiers The paper will be divided into two sections i e a functional description and a discussion of circuit operation Complete construction information will be given including a layout for the tester circuit boards FUNCTIONAL DESCRIPTION The test set operates in one o
f three basic modes These are (1) Bias Current Test (2) Offset Voltage Offset Current Test and (3) Transfer Function Test In the first two of these tests the amplifier under test is exercised throughout its full common mode range In all three tests power supply voltages for the circuit under test may be set at g 5V g 10V g 15V or g 20V
National Semiconductor Application Note 24 M Yamatake April 1986
POWER SUPPLY Basic waveforms and dc operating voltages for the test set are derived from a power supply section comprising a positive and a negative rectifier and filter a test set voltage regulator a test circuit voltage regulator and a function generator The dc supplies will be discussed in the section dealing with detailed circuit description The waveform generator provides three output functions a g 19V square wave a b 19V to a 19V pulse with a 1% duty cycle and a g 5V triangular wave The square wave is the basic waveform from which both the pulse and triangular wave outputs are derived The square wave generator is an operational amplifier connected as an astable multivibrator This amplifier provides an output of approximately g 19V at 16 Hz This square wave is used to drive junction FET switches in the test set and to generate the pulse and triangular waveforms The pulse generator is a monostable multivibrator driven by the output of the square wave generator This multivibrator is allowed to swing from
negative saturation to positive saturation on the positive going edge of the square wave input and has a time constant which will provide a duty cycle of approximately 1% The output is approximately b19V to a 19V
TL H 7190 1
FIGURE 1 Functional Diagram of Bias Current Test Circuit
AN-24
C1995 National Semiconductor Corporation
TL H 7190
RRD-B30M115 Printed in U S A
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