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

Toshihiro KONISHI
Keisuke OKUNO
Shintaro IZUMI

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E96-A    No.2    pp.434-442
Publication Date: 2013/02/01
Online ISSN: 1745-1337
DOI: 10.1587/transfun.E96.A.434
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuit Techniques and Related Topics)
ADC,  TDC,  oscillator,  noise-shaping,  low-power,  small area,  process scalable,  

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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 45 dB is achievable at input bandwidth of 16 kHz and a sampling rate of 8 MHz, where the power is 408.5 µW. Its area is 608 µm2.