Overview

AN420

4/15

Doc ID 2078 Rev 2

2

Overview

The technique implemented is that of the Algebraic Adder, a full discussion of the principle

of operation is included in this note.

A practical example of the external components used is shown in the following figure:

Figure 1.

Example circuit

The resistances are selected by the ST62 I/O pins depending on the analog input voltage.

The selection programmed modifies the output voltage of the OpAmp in such a way that the

following A/D conversion is always made with the maximum input range of the converter.

This selection is made by software, therefore the total conversion time is increased versus a

normal 8-Bit conversion, however the precision is increased and the input voltage range can

be enlarged.

PC4

PC5

PC6

ST6215

PB0 (A/D Input)

Vin

OUTPUTS