A low-power DTOF image sensor with double-frame-multiplexing mode for long-range detection

•A new operation mode of time-to-digital converters to separate the detection of the minimum distance and the depth of field in time-of-flight measurements.•The mode achieves a long detection range with high resolution in a small pixel area.•The mode reduces the power consumption of the readout integrated circuit. A novel time-to-digital converter (TDC) operation mode, called double-frame-multiplexing (DFM), is proposed for time-of-flight (TOF) measurements. It is based on the separate detection of the minimum distance and depth of the measured targets, which reduces the power consumption of in-pixel TDCs and expands the maximum detection distance under high resolution. A 64 × 64 direct TOF image sensor chip is fabricated in a 0.18 μm CMOS process. Driven by a 125 MHz multi-phase clock and a 50 MHz data readout clock, the chip achieves a maximum frame rate of 20 kframe/s, a maximum detection distance of 750 m (5 μs), and a maximum depth of field of 3 m (20 ns) with a temporal resolution of 1 ns. The DFM mode reduces the average power consumption to 60 mW without consideration of SPADs. The worst-case measured differential nonlinearity is −0.61/+0.69 least significant bit (LSB) and the maximum integral nonlinearity is −1.06/+0.66 LSB.