Digital Compensation Method for the Path Delay Mismatches in GRO-TDC

The digital compensation method for path delay mismatches in the time-to-digital converter (TDC) based on gated-ring oscillator (GRO) is proposed and demonstrated. The output of the GRO is digitized by the combination of a counter and a phase-to-digital converter (PDC) producing an integer and a fractional digital value, respectively. Due to the delay mismatches between two paths, the integer and fractional digital values are not synchronized thereby causing calculation errors. In order to reduce the errors, a correction bit (CB) is generated and then the erroneous output is fixed by the additional but simple digital circuits. Measurement results show that calculation errors due to the delay mismatches are corrected by the proposed compensation method and it reduces the quantization noise power by 10dB at high frequency offset.