SSP1922 is a high accurate time measurement (TDC) circuit. SSP1922 integrates analog comparator, analog switch, Schmidt flip-flop and other internal devices, thus greatly simplifying the peripheral circuit. At the same time, the first wave detection function is added inside, so that the anti-interference ability is greatly improved. The programmable offset range of the comparator is increased to ±35mV, the sampling accuracy can be improved.Measuring the relative pulse width of the first wave gives the user an indication of the strength of the received signal. Through this hint, we can judge the abnormal detection of ultrasonic transducer, the increase of wall covering, the presence of bubbles in water and so on. The Start-TOF-Restart command can complete a measurement of ultrasonic time difference (upstream and downstream) and data reading, so as to greatly reduce the software operation and power consumption. Compatible with TDC - GP22.