TC826

DS21477B-page 6

© 2002 Microchip Technology Inc.

3.0

DETAILED DESCRIPTION

3.1

Dual Slope Conversion Principles

The TC826 is a dual slope, integrating analog-to-digital

converter. The conventional dual slope converter mea-

surement cycle has two distinct phases:

• Input Signal Integration

• Reference Voltage Integration (De-integration)

The input signal being converted is integrated for a

clock pulses. An opposite polarity constant reference

voltage is then integrated until the integrator output

voltage returns to zero. The reference integration time

(Figure 3-1).

In a simple dual slope converter, a complete conver-

sion requires the integrator output to ‘ramp-up’ and

‘ramp-down’.

A simple mathematical equation relates the input signal

reference voltage and integration time:

EQUATION 3-1:

FIGURE 3-1:

BASIC DUAL SLOPE CONVERTER

1

RC

0

RC

∫

Where:

(Variable)

+

–

Integrator

REF

Voltage

Switch Driver

+

–

Phase Control

Polarity Control

Control

Logic

Comparator

C

R

Clock

Counter

Display

Analog Input

Signal

+/–

Fixed Signal

Integrate

Time

Variable

Reference

Integrate

Time