The DDC112 is a dual input, wide dynamic range, charge-digitizing 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-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 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 a SO-28 or TQFP-32 package and is offered in two performance grades.