Typical Performance Characteristics–AD7783

–7–

8

7

0

6

5

4

3

2

1

9

TPC 1. Noise Distribution Histogram

ADC CIRCUIT INFORMATION

Overview

The AD7783 incorporates a

S-D ADC channel, on-chip pro-

grammable gain amplifier, and on-chip digital filtering intended

for the measurement of wide dynamic range, low frequency

signals such as those in weigh-scale, strain gage, pressure trans-

ducer, or temperature measurement applications.

This ADC input is buffered and can be programmed to have an

input voltage range of

±160 mV or ±2.56 V. The input channel

is configured as a fully differential input. Buffering the input

channel means that the part can accommodate significant source

impedances on the analog input and that R, C filtering (for

noise rejection or RFI reduction) can be placed on the analog

input if required. The device requires an external reference of

2.5 V nominal. Figure 3 shows the basic connections required

to operate the part.

AD7783

REFIN(+)

REFIN(–)

AIN(–)

AIN(+)

IOUT2

IOUT1

XTAL1

XTAL2

DOUT/

RDY

CS

SCLK

GND

POWER

SUPPLY

10 F

0.1 F

CONTROLLER

32.768kHz

CRYSTAL

6k

10k

IN–

OUT+

OUT–

IN+

Figure 3. Basic Connection Diagram

f

ADC

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32 768 10

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8

3

3

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while the settling time equals

t

f

t

SETTLE

ADC

ADC

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2

2

Normal-mode rejection is the major function of the digital filter

on the AD7783. Simultaneous 50 Hz and 60 Hz rejection of

better than 60 dB is achieved as notches are placed at both 50 Hz

and 60 Hz. Figure 4 shows the filter rejection.

FREQUENCY (Hz)

0

010

40

6080

100

–40

–80

–120

–140

–160

–20

–60

–100

20

30

50

70

90

OUTPUT DATA RATE = 19.8Hz

INPUT BANDWIDTH = 4.74Hz

50Hz REJECTION = –66dB, 50Hz

1Hz REJECTION = –60dB

60Hz REJECTION = –117dB, 60Hz

1Hz REJECTION = –94dB

Figure 4. Filter Profile (Filter Notches at Both

50 Hz and 60 Hz)

2.5

0

1.0

3.0

2.5

2.0

1.5

3.5

5.0

4.5

4.0

2.0

1.5

1.0

0.5

3.0

160mV RANGE

2.56V RANGE

TPC 2. RMS Noise vs. Reference Input

REV. C