The RES11A can be used to in conjunction with a dual-channel operational amplifier to implement a discrete instrumentation amplifier (INA). The ratiometric matching between the two resistor dividers improves CMRR performance for the circuit when compared to a similar implementation using unmatched discrete resistors, and results in better overtemperature and overaging gain drift characteristics. INAs are often used instead of difference amplifiers when high input impedance and low bias currents are needed, such as when measuring bridge sensors.

Discrete INAs are often configured as a differential-input differential-output circuit as shown in Figure 8-3. While not shown, if needed, use an additional discrete difference amplifier stage (requiring a second RES11A and another op-amp channel) to convert the differential output voltage to a single-ended voltage (for example, when driving a single-ended ADC). This extra stage can also add an additional offset and provide additional gain, effectively mimicking the common three-amplifier INA architecture.

Figure 8-3 Differential-Input, Differential-Output Instrumentation Amplifier Using the RES11A

Less commonly, a discrete INA can be implemented as a differential-input, single-ended output circuit as shown in Figure 8-4. This topology maintains high input impedances, allows an offset to be applied, and gives a single-ended output without requiring a third amplifier channel. The offset must be driven by a low-impedance source, such as a reference buffer. When designing a discrete INA, carefully consider the output swing and input common-mode range limitations of the amplifiers used in the circuit design process.

Figure 8-4 Differential-Input, Single-Ended Output Instrumentation Amplifier Using the RES11A