This document describes how the on-chip 8-bit A/D converter of the ST62 can be used to expand its resolution to a higher resolution
The document details a method for achieving higher than 8-bit Analog-to-Digital conversion resolution on the ST62 microcontroller. This is accomplished by utilizing an external Operational Amplifier (OpAmp) and specific resistor configurations to create an algebraic adder circuit.
The technique involves switching between different voltage sources under software control to scale the input signal into smaller ranges that fit within the converter's maximum input range. By performing multiple conversions with these scaled inputs, the system effectively increases the total resolution beyond the native 8-bit capability of the chip.
Higher resolution is achieved by using an external Operational Amplifier and resistors to create an algebraic adder that scales the input voltage into smaller ranges for conversion.
The technique requires an additional Operational Amplifier and a few resistors to be connected externally to the microcontroller.
The selection of voltage sources is made by software, which increases the total conversion time compared to a normal 8-bit conversion but allows for increased precision.