Digital compensation method for the path delay mismatches in GRO-TDC

The digital compensation method for path delay mismatches in 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 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 is generated and then the erroneous output is fixed based on the correction bit by the additional but simple digital circuits. Measurement results show that many calculation errors are corrected by the proposed compensation method reducing the quantization noise power by 10dB at high frequency offset.