Time-of-flight distance sensor with MOSFET lowpass filter as key element for suppression of ambient light

A lowpass filter consisting of small MOSFET transistors is presented for application in a time-of-flight distance sensor. As a decision-making element, it activates the mechanism for background-light suppression in combination with some logic components. The cutoff frequency around 1 MHz is designed to smooth a signal with 10 MHz ripple. A filter attenuation of -35 dB/decade is achieved at smaller area compared to an RC-filter of only first order in the used 0.6 m BiCMOS technology. The functionality is proven by distance measurements up to 150 klx of extraneous light with centimetre accuracy, exceeding the performance of existing sensors.