FEATURES

MONOLITHIC CHARGE MEASUREMENT A/D

CONVERTER

DIGITAL FILTER NOISE REDUCTION:

3.2ppm, rms

INTEGRAL LINEARITY:

±0.005% Reading ±0.5ppm FSR

HIGH PRECISION, TRUE INTEGRATING FUNCTION

PROGRAMMABLE FULL-SCALE

SINGLE SUPPLY

CASCADABLE OUTPUT

APPLICATIONS

DIRECT PHOTOSENSOR DIGITIZATION

CT SCANNER DAS

INFRARED PYROMETER

PRECISION PROCESS CONTROL

LIQUID/GAS CHROMATOGRAPHY

BLOOD ANALYSIS

DESCRIPTION

The DDC112 is a dual input, wide dynamic range, chargedigitizing

analog-to-digital (A/D) converter with 20-bit resolution.

Low-level current output devices, such as photosensors,

can be directly connected to its inputs. Charge integration is

continuous as each input uses two integrators; while one is

being digitized, the other is integrating.

For each of its two inputs, the DDC112 combines current-tovoltage

conversion, continuous integration, programmable

full-scale range, A/D conversion, and digital filtering to achieve

a precision, wide dynamic range digital result. In addition to

the internal programmable full-scale ranges, external integrating

capacitors allow an additional user-settable full-scale

range of up to 1000pC.

To provide single-supply operation, the internal A/D converter

utilizes a differential input, with the positive input tied to VREF.

When the integration capacitor is reset at the beginning of

each integration cycle, the capacitor charges to VREF. This

charge is removed in proportion to the input current. At the

end of the integration cycle, the remaining voltage is compared

to VREF.

The high-speed serial shift register which holds the result of

the last conversion can be configured to allow multiple DDC112

units to be cascaded, minimizing interconnections. The

DDC112 is available in an SO-28 or TQFP-32 package and is

offered in two performance grades.