A second-order noise-shaping time-to-digital converter using switched-ring oscillator

A high-resolution time-to-digital converter (TDC) using switched-ring oscillator (SRO) is presented. The proposed TDC relies on oversampling and second-order noise-shaping to achieve the targeted resolution without the need for calibration. The theory as well as the comparison with existing techniques are presented in this paper. In addition, the circuit implementation using 130 nm CMOS process is demonstrated. The proposed TDC operates over a wide range of input carrier frequencies (0.6-750 MHz) and sampling rates (50-750 MS/s). Simulation results show that, at 500 MS/s and 80 MHz carrier frequency, integrated noise (effective TDC resolution) of 157 fs, 271 fs, and 375 fs are achieved with integrated bandwidths of 1 MHz, 5 MHz and 10 MHz, respectively. The proposed TDC consumes 1.7 mW from 1.2 V supply.