A 3- μs Row-Time Analog-Based Phase Calculation Circuit for Indirect Time-of-Flight 3-D Image Sensor

Abstract

In indirect time-of-flight (i-ToF) image sensors, multiphase signal calculation often requires multiple readout circuits and large-scale digital circuits. In this article, an analog-based phase calculation (A-PC) readout circuit with a 3- $\mu $ s row time for an i-ToF 3-D image sensor is proposed. The circuit achieves the calculation of multiphase signals into a single signal corresponding to the real phase by performing voltage-current–voltage conversion with an adder-based compensation circuit in the analog domain. Additionally, a linearity correction method is introduced to enhance circuit accuracy. The A-PC circuit is designed in a 110-nm 1P4M CMOS technology, achieving a row conversion time of $3~\mu $ s. The simulation results indicate a linearity of 99.69% with an average power consumption of $210~\mu $ W per column. The proposed approach reduces the power consumption by decreasing the number of analog-to-digital converters (ADCs) in the analog domain and minimizing the large amount of data in the digital domain, thereby significantly lowering overall sensor power consumption. Using reported ADCs as column-parallel ADCs in the proposed analog-based i-ToF calculation system, the method achieves a 26.3%–48.4% power reduction compared to the conventional digital-based method.