A second-order bandpass ΔΣ time-to-digital converter with negative time-mode feedback

This paper presents an all-digital bandpass ΔΣ time-to-digital converter (BP)ΔΣTDC) for IF data conversion. The proposed TDC is based on a second-order resonator implemented by a cascade of two time-mode lossless discrete integrators (LDI), and a digital-to-time converter (DTC) in a feedback loop. The DTC is based on a new topology of doubleedge voltage-controlled delay unit. The proposed TDC achieves bandpass quantization noise shaping and it does not require any complex calibration circuit to compensate for timing errors. To realize the time-mode LDI-based resonator, time-latches with some digital gates are employed. Moreover, a direct feed-forward compensation is utilized in the TDC to attain high signal-tonoise and distortion ratio (SNDR) by reducing the internal timemode swing, thus relaxing the speed and area requirements on digital circuits leading to low-voltage operation. The prototype BPΔΣTDC achieves a 39.5-dB peak SNDR over a 0.2 MHz signal bandwidth at 42.8 MS/s while consuming less than 5 mW in a 1.2 V IBM 130-nm CMOS process. The proposed TDC is highly digital and occupies a core area of only 0.048 mm.