An 8-channel 16 b charge-to-digital converter for imaging applications

An 8-channel 16-b charge-to-digital converter is described. Phothomic signals are inherently quantized and Poisson-noise limited. The diagram presented plots as binary exponents both the output code and the number of input electrons for signals converted by a multichannel, fully parallel floating-point CDAS (charge-input data acquisition system) chip containing 8 ADCs (analog-to-digital converters). These converters use the RipSaw algorithm, named for the circular-saw-blade shape of the characteristic voltage-conversion waveform. The analog signal processor for each pipelined conversion channel is shown. Bandlimited integrators combined with dual, noise-shaping SHAs allow each channel to achieve a 55-kHz NEB (noise effective bandwidth) at 20 kS/s. The analog signal processor is combined with the RipSaw mantissa, exponent, and control logic to complete one CDAS channel. Each of the twelve switches in every CDAS is charge-compensated with slew rate and differential delay adjusted to optimized charge injection and/or partition noise.<>