High Resolution Mixed-Domain Delta-Sigma Time-to-Digital Converter Using Compensated Charge-Pump Integrator

Zule XU

IEICE TRANSACTIONS on Electronics   Vol.E100-C    No.6    pp.548-559
Publication Date: 2017/06/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E100.C.548
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuits and Their Application Technologies)
charge-pump,  delta-sigma,  SAR ADC,  time-to-digital converter,  

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This paper presents a high resolution mixed-domain Delta-Sigma (ΔΣ) time-to-digital converter (TDC) which utilizes a charge pump as time-to-voltage converter, a low resolution SAR ADC as quantizer, and a pair of delay-line digital-to-time converters to form a negative feedback. By never resetting the sampling capacitor of the charge-pump, an integrator is realized and first order noise shaping can be achieved. However, since the integrating capacitor is never cleared, this circuit is prone to charge-sharing issue during input sampling which can degrade TDC's performance. To deal with this issue, a compensation circuit consists of another pair of sampling capacitors and charge-pumps with doubled current is proposed. This TDC is designed and simulated in 65 nm CMOS technology and can operate at 200 MHz sampling frequency. For 2.5 MHz bandwidth, simulation shows that this TDC achieves 66.4 dB SNDR and 295 fsrms integrated noise for ±1 ns input range. The proposed TDC consumes 1.78 mW power that translates to FoM of 208 fJ/conv.