DDC112

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 program-mable 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 of DDC112 utilizes a differential input, with the positive input tied to V_REF . When the integration capacitor is reset at the beginning of each integration cycle, the capacitor charges to V_REF . This charge is removed in proportion to the input current. At the end of the integration cycle, the remaining voltage is compared to V_REF.

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 a SO-28 package and is offered in two performance grades.