1.2.1 Buffering with an Operational Amplifier

Op amps have high input impedances and low output impedances, which makes them ideal for buffering signals. While Microchip has a wide variety of discrete op amps, certain microcontroller families contain embedded op amps that reduce the Bill of Materials (BOM). However, discrete op amps generally have higher analog performance than embedded op amps.

Op amps can lower a signal's source impedance for faster acquisition times (see Signal Impedance and Acquisition Time) and isolate the input signal from the capacitive dip caused by the ADC charging its capacitor. However, op amps add noise and offset to their output, which may reduce the Signal-to-Noise Ratio (SNR). If the input signal is low-impedance, then there is little benefit in buffering with an op amp. However, if the input signal is high-impedance, the op amp can significantly improve acquisition times. A simple unity gain (also called voltage follower) configuration of the op amp is shown in Figure 1-2.