On-focal-plane ADC: recent progress at JPL

Two 8 bit successive approximation analog-to-digital converters (ADC), an 8 bit single slope ADC and a 12 bit current mode incremental sigma delta ((Sigma) -(Delta) ) ADC have been designed, fabricated, and tested. The 20.4 micrometers and 40 micrometers pitch successive approximation test chip designs are compatible with active pixel sensors (APS) column parallel architectures. A 64 X 64 photogate APS with this ADC integrated on-chip was fabricated in a 1.2 micrometers N-well CMOS process and achieves 8 bit accuracy. A 1 K X 1 K APS with 11 micrometers pixels and a single slope ADC in each column was fabricated in a 0.55 micrometers N-well CMOS process and also achieves 8 bit accuracy. The successive approximation designs consume as little as 49 (mu) W at a 500 KHz conversion rate meeting the low power requirements inherent in column parallel architectures. The current mode (Sigma) -(Delta) ADC test chip is designed to be multiplexed among 8 columns in a semi-column parallel current mode APS architecture. It consumes 800 (mu) W at a 5 KHz conversion rate.

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