An Adaptive AFE Circuit to Minimize the Zero-Flow Error in Transit-Time Ultrasonic Water Flowmeter

This paper presents an adaptive analog front end (AFE) circuit for ultrasonic water flowmeter application, including a programmable gain amplifier (PGA) and a low delay dispersion comparator (LDD-CMP). The gain of the PGA is adaptively controlled by a peak detector to minimize the input amplitude variation of the comparator. As to the LDD-CMP, an adaptive current regulating circuit is designed for the conventional two-stage open-loop comparator to reduce the propagation delay dispersion caused by the different input overdrive. The proposed AFE has been fabricated in a $180-\mathrm{nm}$ CMOS technology, and the measurement results show that the zero-flow error of the ultrasonic flowmeter ASIC with the proposed AFE is only $6.3 \%$ of that of the one with a conventional comparator, and $6.2 \%$ of the commercial product TDC-GP22, with input frequency at 1 MHz.