关键词: 像素级TAC, 双斜坡, DAC, 三角波, 阶梯波

Abstract: This paper is aimed at 3D imaging laser focal plane readout circuit,traditional in-pixel time amplitude converter (TAC) has the contradiction between accuracy and dynamic range. Therefore,a in-pixel TAC based on dual slope sampling technique is proposed.The proposed in-pixel TAC scheme simultaneously samples the voltage values of the low-slope step wave and the high-slope triangular wave in the required sampling time interval. The step wave voltage value of the sample tocoarse interval of time,then the triangular wave sampling voltage value finely quantify the time interval. Due to the coarse and fine quantification of the two slopes, the quantitative accuracy is enhanced, while effectively improving the dynamic range. The step wave is realized by the current steering DAC with thermometer coding method, ensuring the unity of logic timing and step wave accuracy. The proposed TAC is based on0.18μm CMOS process, the quantization precision is 14 bits with quantization voltage 11.7mV,the minimum resolution accuracy reached 500ps, and the dynamic range up to 8μs. The scheme is very suitable for high speed 3D imaging applications, such as vehicle lidar.

Key words: in pixel TAC, double slope, DAC, triangular wave, step wave