A Low-Offset VCO-Based Time-Domain Comparator Using a Phase Frequency Detector With Reduced Dead and Blind Zones

Abstract

We present in this paper a high-precision voltage-controlled oscillators (VCO)-based time-domain (TD) comparator. It involves two identical and linear VCOs to convert the input voltage difference of the comparator into the time/frequency difference. Also, it includes a novel low-power phase frequency detector (PFD) to compare the output frequencies of the VCOs. The proposed PFD technique reduces the problematic effects of missing edges and phase ambiguity in conventional circuits by minimizing dead-zone (DZ)/blind-zone (BZ) and suppressing unwanted output glitches. The TD-comparator prototype is fabricated in a 350 -nm CMOS process having an active area of 0.01 mm2. The comparator consumes 93.65 μ W power from a 3.3 -V supply and provides a conversion rate of 2.7 MHz with 148 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\mu }\mathbf {V_{rms}}$ </tex-math></inline-formula> input-referred noise. Measurement results of 5 fabricated chips show an input-referred offset standard deviation of 81.14 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mu }\text{V}$ </tex-math></inline-formula> . Stand-alone characteristics measurements of the proposed PFD show a minimized DZ and BZ of less than 12 and 22.7 ps, respectively. With an almost <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\pm 2\pi }$ </tex-math></inline-formula> input phase range, the maximum operating frequency of the PFD is 1.32 GHz.