A Second-Order All-Digital TDC with Low-Jitter Frequency Shift Oscillators and Dynamic Flipflops

Toshihiro KONISHI
Keisuke OKUNO
Shintaro IZUMI

IEICE TRANSACTIONS on Electronics   Vol.E96-C    No.4    pp.546-552
Publication Date: 2013/04/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E96.C.546
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Solid-State Circuit Design—Architecture, Circuit, Device and Design Methodology)
ADC,  TDC,  oscillator,  digital circuit,  adaptive LMS filtering,  

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We present a small-area second-order all-digital time-to-digital converter (TDC) with two frequency shift oscillators (FSOs) comprising inverter chains and dynamic flipflops featuring low jitter. The proposed FSOs can maintain their phase states through continuous oscillation, unlike conventional gated ring oscillators (GROs) that are affected by transistor leakage. Our proposed FSOTDC is more robust and is eligible for all-digital TDC architectures in recent leaky processes. Low-jitter dynamic flipflops are adopted as a quantization noise propagator (QNP). A frequency mismatch occurring between the two FSOs can be canceled out using a least mean squares (LMS) filter so that second-order noise shaping is possible. In a standard 65-nm CMOS process, an SNDR of 61 dB is achievable at an input bandwidth of 500 kHz and a sampling rate of 16 MHz, where the respective area and power are 700 µm2 and 281 µW.