DDC112

® DDC112 DDC 112 For most current data sheet and other product information, visit www.burr-brown.com Dual Current Input 20-Bit ANALOG-TO-DIGITAL CONVERTER FEATURES q MONOLITHIC CHARGE MEASUREMENT ADC q DIGITAL FILTER NOISE REDUCTION: 3.2ppm, rms q INTEGRAL LINEARITY: ±0.005% Reading ±0.5ppm FSR q HIGH PRECISION, TRUE INTEGRATING FUNCTION q PROGRAMMABLE FULL SCALE q SINGLE SUPPLY q CASCADABLE OUTPUT DESCRIPTION The DDC112 is a dual input, wide dynamic range, charge-digitizing analog-to-digital converter (ADC) 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-to-voltage 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 ADC 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 remainin...