A Two-Step Time-to-Digital Converter With 5.6-ps Resolution and 1-4255-s Measurement Range

This brief presents a two-step coarse-fine time -todigital converter (TDC) for ultrasonic flowmeter applications. To achieve a high resolution with a low frequency reference clock, a 7.7 -MHz reference frequency is multiplied by 32 times using a multiplying delay-locked loop (MDLL) to generate a high -speed internal clock for coarse quantization. The resulting residual time error after coarse quantization is pulse-stretched and finely quantized. A cost-effective calibration scheme is proposed to ensure the PVT robustness of the pulse stretching circuit. The proposed TDC is realized in a 0.11 mu m/1.5V CMOS technology. It achieves a resolution of 5.6ps with a wide input range from 1 to 4255 mu s. The core TDC circuit occupies 0.065 mm2 and consumes 1.8mW. The measured differential nonlinearity and integral nonlinearity is +/- 3.1ps and +/- 59.7ps respectively.