20-BIT ANALOG-TO-DIGITAL CONVERTER

DDC101

DESCRIPTION

The DDC101 is a precision, wide dynamic range, charge

digitizing A/D converter with 20-bit resolution. Low

level current output devices, such as photosensors, can be

directly connected to its input. The most stringent accu-

racy requirements of many unipolar output sensor appli-

cations occur at low signal levels. To meet this require-

ment, Burr-Brown developed the adaptive delta modula-

tion architecture of the DDC101 to provide linearly

improving noise and linearity errors as the input signal

level decreases. The DDC101 combines the functions of

current-to-voltage conversion, integration, input program-

mable gain amplification, A/D conversion, and digital

filtering to produce precision, wide dynamic range re-

sults. The input signal can be a low level current con-

nected directly into the unit or a voltage connected

through a user selected resistor. Although the DDC101 is

optimized for unipolar signals, it can also accurately

digitize bipolar input signals. The patented delta modula-

tion topology combines charge integration and digitiza-

tion functions. Oversampling and digital filtering reduce

system noise dramatically. Correlated Double Sampling

(CDS) captures and eliminates steady state and conver-

sion cycle dependent offset and switching errors that are

not eliminated with conventional analog circuits.

The DDC101 block diagram is shown below. During

conversion, the input signal is collected on the internal

integration capacitance for a user determined integration

period. A high precision, autozeroed comparator samples

the analog input node. Tracking logic updates the internal

high resolution D/A converter at a 2MHz rate to maintain

the analog input at virtual ground. A user programmable

digital filter oversamples the tracking logic’s output. The

digital filter passes a low noise, high resolution digital

output to the serial I/O register. The serial outputs of

multiple DDC101 units can be easily connected together

in series or parallel if desired to minimize interconnections.

q MONOLITHIC CHARGE INPUT ADC

q DIGITAL FILTER NOISE REDUCTION:

0.9ppm, rms

q DIGITAL ERROR CORRECTION: CDS

q CONVERSION RATE: Up to 15kHz

q USER FRIENDLY EVALUATION FIXTURE

APPLICATIONS

FEATURES

q DIRECT PHOTOSENSOR DIGITIZATION

q PRECISION INSTRUMENTATION

q INFRARED PYROMETRY

q PRECISION PROCESS CONTROL

q CT SCANNER DAS

q CHEMICAL ANALYZERS

C

INT

Digital Integration,

Tracking and

Control Logic

Digital Filter and

Error Correction

Serial I/O

Register

Serial In

Serial Out

Reset

DAC

CDAC

DDC101 Integrated Circuit

Comparator

V

REF

Analog

Input

Ground

Setup

Oversampled

Digital Out

18 Bits

20 Bits

Test In

+V

S

Test Current

©1993 Burr-Brown Corporation

PDS-1211E

Printed in U.S.A. March, 1998

®

International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111

Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132

DDC101

SBAS029