FEATURES

MONOLITHIC CHARGE INPUT ADC

DIGITAL FILTER NOISE REDUCTION:

0.9ppm, rms

DIGITAL ERROR CORRECTION: CDS

CONVERSION RATE: Up to 15kHz

USER FRIENDLY EVALUATION FIXTURE

APPLICATIONS

DIRECT PHOTOSENSOR DIGITIZATION

PRECISION INSTRUMENTATION

INFRARED PYROMETRY

PRECISION PROCESS CONTROL

CT SCANNER DAS

CHEMICAL ANALYZERS

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 accuracy

requirements of many unipolar output sensor applications

occur at low signal levels. To meet this requirement,

Burr-Brown developed the adaptive delta modulation

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 programmable

gain amplification, A/D conversion, and digital

filtering to produce precision, wide dynamic range results.

The input signal can be a low level current connected

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 modulation

modulation

topology combines charge integration and digitization

functions. Oversampling and digital filtering reduce

system noise dramatically. Correlated Double Sampling

(CDS) captures and eliminates steady state and conversion

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.