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# Level Shifting Amplifier With Constant Gain

IP.com Disclosure Number: IPCOM000052966D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 2 page(s) / 23K

IBM

## Related People

Driscoll, CD: AUTHOR [+2]

## Abstract

This article describes a level shifting amplifier in which the values of resistors are chosen to provide constant amplifier gain, that is, gain unaffected by the operating point.

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Level Shifting Amplifier With Constant Gain

This article describes a level shifting amplifier in which the values of resistors are chosen to provide constant amplifier gain, that is, gain unaffected by the operating point.

The general function of a level shifting amplifier is to convert a floating input voltage (not referenced to ground) to voltages which are referenced to ground. The drawing illustrates a level shifting amplifier. The output voltage V0 produced by this amplifier is determined by the equation: The equation shows that the output voltage V0 is a function of the absolute values of V1 and V2. As V1 and V2 change, V0 also changes even if the input voltage E remains constant. That is, the gain of the circuit is generally a function of the operating point.

For selected values of resistors, however, the illustrated circuit can operate at a gain G independent of the absolute magnitudes of the input voltages V1 and V2, provided the resistors have the values indicated below, where A and B are fixed ohmic levels: If the values given above are substituted into equation (1), it will be seen that the gain G (V0/E) is independent of the absolute magnitudes of V1 and V2.

By choosing the relative values of A and B appropriately, the voltages V+ and V- at the inputs to the operational amplifier can be limited to values compatible with the operational amplifier's specifications. The values V+ and V- should equal one another, both being a function of V2 as indicated...