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Gain Change Amplifier

IP.com Disclosure Number: IPCOM000093455D
Original Publication Date: 1967-Sep-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Hollstein, CP: AUTHOR

Abstract

This circuitry effects gain change without changing resistors R1 and R2 in the feedback loop.

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Gain Change Amplifier

This circuitry effects gain change without changing resistors R1 and R2 in the feedback loop.

Differential input stages 10 are connected in common to input terminals 11 and 12. These stages are also connected in parallel to the input of amplifier 14 and associated feedback stage 16. The differential input, single-ended output arrangement permits input terminals 11 and 12 to move with common mode voltages. The feedback is referenced to ground or to a point other than that of the input signal as desired. The ratio of the values of the feedback resistors R1 and R2 is equivalent to the ratio of feedback voltage to the output voltage. Constant current circuit 18 is connected in the feedback stage 16. Similar constant current circuits 20 are provided for input stages 10. The latter have switch transistors 22 interposed in them. Switching element 24 is arranged to enable only one of the input stages 10 at a time by turning on the associated switch transistor 22. This switching element 24 is a part of a known device coupled to output terminals 31 and 32. A range of input voltages is selected for amplification, by amplifier 14, to a predetermined narrow range of levels desired at output terminals 31 and 32.

The ratio of the values of the resistors Ra, Rb, Rc of the input stages to resistor R3 of the feedback stage is equivalent to the gains. The output voltage is then Eout= Ein >(R1 + R2)/R2|>R3/Rg| where Rg is the value of Ra when stage 10a is e...