This article describes how to extend the common-mode input range of difference amplifiers for use in a wider variety of reduced power-supply applications. By offsetting or dynamically adjusting the common-mode range, the common-mode input range can be increased in reduced power supply applications.
This application bulletin explains how to increase the usable common‑mode voltage range of Texas Instruments INA117 (and INA105) difference amplifiers for reduced‑power‑supply designs. Two main techniques are covered: offsetting the reference voltage with a fixed offset and dynamically adjusting the reference to follow the input signal.
The document provides circuit examples, equations for calculating the extended range, and tables showing the resulting common‑mode limits for various supply voltages. It also includes practical design notes on output swing limits and component selection.
| Common‑mode input range (standard +15 V supply) | +200 V |
|---|---|
| Maximum rated operating voltage | +200 V |
| Output swing on +15 V supply | at least +10 V |
| Negative output swing limit | to within 3 V of the negative rail (e.g., –12 V on +15 V) |
It is specified as +200 V.
By either offsetting the reference voltage with a constant voltage or dynamically adjusting the reference to follow the input signal.