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VCO-based ADCs has long existed as an alternative way of digitization of analog signal. Thanks to its time-domain operation, VCO-based structures using phase domain signal processing have become very promising in highly scaled CMOS processes. The general idea is that since voltage-domain quantization is increasingly difficult to do well in scaled CMOS processes with low supply voltages, it is potentially a better idea to exploit what scaled CMOS processes are very good at: having lots of small transistors that switch fast. Thus, translating input voltage variations to a corresponding phase/frequency variation puts information into the time domain, which can be easily quantized via simple digital circuitry. On the other hand, one well known issue of VCOs is the non-linear voltage-to-frequency transfer characteristic, particularly when input amplitude is large. The distorted frequency output ultimately translates to a …