| Analog to digital converters (ADCs) are the link of the analog world with the digital world of signal processing. Therefore practically every digital system that interacts with the outside (analog world) needs ADCs.; Commonly used ways to implement ADCs range from flash ADCs, which convert an input signal in one single clock cycle, to successive approximation ADCs, which produce one output bit per clock cycle.; In this work we present a novel capacitive circuit architecture for compact high-speed ADCs, which is based on cascade-connected capacitive threshold gates. This so-called “ripple-flash” ADC circuit is realized using conventional CMOS technology, offers very small layout area, simple operational characteristics, low power dissipation, and a high input-to-output response speed.; Several variants of 3-, 4-, and 5-bit ADCs have been fabricated and tested to exhibit accurate DC transfer characteristics, and typical transient response times in the order of 40 ns and sampling frequencies of 20 MHz for the 4-bit ADC. The proposed ADC circuits can also be used as building blocks in high-speed pipelined ADC architectures with higher accuracy. |
