# 8.8 Driving SAR ADC Without Amplifiers

## Description

This video shows how to select the resistor and capacitor for good settling on SAR ADC without amplifiers. Some common examples of SAR ADC usage without amplifiers are monitoring power supplies or monitoring a slow moving sensor such as a thermistor. In previous videos we learned how to select the amplifier and external RC filter to achieve good settling. In these videos we used simulation and a parametric search to find the optimal RC value. Although this method can be used on circuits without amplifiers, it is much easier to use some simple equations to select the values. The reason the simple equations can be used here but not for circuits using amplifier drive is that circuits without amplifiers are simple first order circuits and amplifier circuits are higher order more complex systems. The higher order systems are difficult to model mathematically as they depend on many factors such as gain and output load. The first order system on the other hand has a simple mathematical solution that yields a set of equations that can be used to find the RC filter and sampling rate needed for proper settling.