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

In i-ToF image sensors, multi-phase signal calculation often requires multiple readout circuits and large-scale digital circuits. In this paper, an analog-based phase calculation readout circuit with a 3 μs row time for an indirect time-of-flight (i-ToF) 3D image sensor is proposed. The circuit achieves the calculation of multi-phase 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 analog-based phase calculation circuit is designed in a 110 nm 1P4M CMOS technology, achieving a row conversion time of 3 μs. Simulation results indicate a linearity of 99.69% with an average power consumption of 210 μW per column. The proposed approach reduces the power consumption by decreasing the number of analog to digital converters (ADC) 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% to 48.4% power reduction compared to conventional digital-based method.