Time-Domain Multi-bit ΔΣ Analog-to-Digital Converter

A multi-bit representation in the time domain has been applied to a Delta Sigma analog-to-digital converter (ADC), which consists of an asynchronous Delta Sigma modulator (ADSM) and a time-to-digital converter (TDC). Current-mode circuits are included in the ADSM to suppress the variation in the node voltage. The TDC is based on a ring oscillator-based TDC comprised of four stages of differential delay element followed by a counter and a phase detector. The 1st-order noise-shaping was experimentally obtained for the TDC fabricated by using 0.18-mu m standard CMOS technology. A successful operation of the ADC has been obtained by transistor-level circuit simulation.