An Opampless Second-Order MASH ΔΣ ADC with Using Gated Ring Oscillator Time-to-Digital Converter

This paper presents a second-order ΔΣ analog-to-digital converter (ADC) operating in a time domain. In the proposed ADC architecture, a voltage-controlled delay unit (VCDU) converts an input analog voltage to a delay time. Then, the clocks outputs from a gated ring oscillator (GRO) are counted during the delay time. No switched capacitor or opamp is used. Therefore, the proposed ADC can be implemented in a small area and with low power. For that reason, it has process scalability: it can keep pace with Moore's law. A time error is propagated to the second GRO by a multi-stage noise-shaping (MASH) topology, which provides second-order noise-shaping. In a standard 40-nm CMOS process, a SNDR of 45dB is achievable at input bandwidth of 16kHz and a sampling rate of 8MHz, where the power is 408.5µW. Its area is 608µm2.