1 Buffering and Scaling Signals with an Operational Amplifier (OPA/OPAMP)

One of the most common use-cases for the internal operational amplifier peripheral is to buffer or scale an input signal to improve signal resolution and/or ADC acquisition time. (This assumes the impedance of the input signal is higher than that of the OPAMP’s output impedance.) Signal resolution can be improved by using an operational amplifier (OPA/OPAMP) with an internal resistor ladder to dynamically scale the input signal to the measurement range of the ADC. In this configuration, the OPAMP acts like a Programmable Gain Amplifier (PGA) for the ADC.

The OPAMP can also be used to reduce the acquisition time required to measure the input signal. Without an OPAMP, a high impedance input signal would have to directly charge the sample and hold (S/H) capacitor inside of the ADC. This increases the required signal acquisition time and loads down the signal. But with an OPAMP buffer, the S/H capacitor is charged quickly while also isolating the input from the capacitive load. The OPAMP buffer's inputs are high impedance, which keeps the input signal from being loaded, while the output is low impedance to quickly charge the S/H capacitor.