3-241

TELCOM SEMICONDUCTOR, INC.

7

6

5

4

3

1

2

8

INTEGRATE

DEINTEGRATE

TIME

CLOCK PULSES

OVERSHOOT DUE TO ZERO CROSSING

BETWEEN CLOCK PULSES

INTEGRATOR RESIDUE VOLTAGE

OVERSHOOT CAUSED BY

COMPARATOR DELAY OF

1 CLOCK PULSE

Figure 10.

Accuracy Errors in Dual-Slope Conversion

Figure 11. Integrator Waveform

INT1

INTEGRATE

DE1

DEINTEGRATE

REST X10

ZERO

INTEGRATE

AND LATCH

DE2 REST X10

DE3

ZERO INTEGRATE

INTEGRATOR

RESIDUAL VOLTAGE

TC7129

in time and amplitude.

Inside the TC7129

Figure 12 shows a simplified block diagram of the

TC7129.

Integrator Section

The integrator section includes the integrator, compara-

tor, input buffer amplifier, and analog switches used to

change the circuit configuration during the separate mea-

surement phases described earlier.

Digital Auto-Zeroing

To eliminate the effect of amplifier offset errors, the

TC7129 uses a digital auto-zeroing technique. After the

input voltage is measured as described above, the mea-

surement is repeated with the inputs shorted internally. The

reading with inputs shorted is a measurement of the internal

errors and is subtracted from the previous reading to obtain

a corrected measurement. Digital auto-zeroing eliminates

the need for an external auto-zeroing capacitor used in other

ADCs.

TC7129

4-1/2 DIGIT ANALOG-TO-DIGITAL

CONVERTER WITH ON-CHIP LCD DRIVERS