INDEPENDENT_SIGNALS

Published:2009/6/29 1:49:00 Author:May | From:SeekIC

Single AD521 instrumentation amplifier compares two independent signal levels from sources having no common reference point. When one differential signal is applied to usual input of opamp and other to reference input, output is proportional to difference. Positive feedback provides small amount of hysteresis, to eliminate ambiguity and reduce noise susceptibility. Stable threshold of about 25 mV is derived from AD580 low-oltage reference circuit. Reference voltage is 2.5 V, but values used for RSand RG are in ratio of 1 :100 so comparator output switches when normal input is about 1/100 of reference input.Output is negative when normal input is zero, and switches positive when input exceeds threshold. Output swings ±12 V as inputs go through critical ratio. R3 and D1 provide TTL-compatible second output.—A. P. Brokaw, You Can Compare Two Independent Signal Levels with Only One IC, EDN Magazine, Apri15, 1975, p 107－108.



Reprinted Url Of This Article:
http://www.seekic.com/circuit_diagram/Amplifier_Circuit/INDEPENDENT_SIGNALS.html

Print this Page | Comments | Reading(3)