5

®

ADS1201

FIGURE 1. Connection Diagram for the ADS1201 Delta-Sigma Modulator Including External Processor.

110

105

100

95

90

85

80

CMRR vs V

DIN

V

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

ADS1201

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

AV

DD

REF

OUT

REF

IN

NIC

A

A

AGND

V

BIAS

REF

EN

MOUT

MCLK

DV

DD

DGND

CAL

GAIN/OFFSET

BIAS

EN

Processor

200

Ω

Analog Supply

10

µF

0.1

µF

Digital

Supply

200

Ω

0.1

µF

47pF

47pF

GENERAL DESCRIPTION

The ADS1201 is a single channel, second-order, CMOS

analog modulator designed for high resolution conversions

from dc to 1000Hz. The output of the converter (MOUT)

provides a stream of digital ones and zeros. The time

average of this serial output is proportional to the analog

input voltage. The combination of an ADS1201 and a

processor that is programmed to implement a digital filter

results in a high resolution A/D converter system. This

system allows flexibility with the digital filter design and is

capable of A/D conversion results that have a dynamic range

that exceeds 130dB (see Figure 1).

THEORY OF OPERATION

The differential analog input of the ADS1201 is imple-

mented with a switched capacitor circuit. This switched

capacitor circuit implements a 2nd-order modulator stage

which digitizes the input signal into a binary output stream.

The input stage of the converter can be configured to sample

an analog signal or to perform a calibration which quantifies

offset and gain errors. The sample clock (MCLK) provides

the switched capacitor network and modulator clock signal

for the A/D conversion process, as well as the output data

framing clock. Different frequencies for this clock allows

for a variety of performance solutions in resolution and

signal bandwidth. The analog input signal is continuously

sampled by the A/D converter and compared to an internal

or external voltage reference. A digital stream appears at the

output of the converter. This digital stream accurately repre-

sents the analog input voltage over time.