Design And Application Research Of Time-to-Digital Converter

Compared with 2D imaging technology, depth of field data is introduced into 3D imaging technology, a more realistic visual experience is provided to the user, which is favorable to people. 3D imaging sensor has a broad market prospect, which can be seen from the popularity of 3D movies. As an advanced three-dimensional imaging method, the direct flight time method has some special advantages, such as high measurement accuracy, high speed, small size and high system robustness. The system has a very important research significance. Photon transmits in space at the speed of light, direct time of flight method can obtain accurate time from the emission light pulses to the echo pulse received by the sensor, and the time can be converted to distance, so as to obtain the depth of field data. Therefore, it is the key to design a high precision time interval measurement circuit to realize the direct flight time method.In this paper, aimed at the background of the application of 3D imaging, a deep research of time-to-digital converter has been carried out, a various kinds of time-to-digital converter have been analyzed, contrast them in terms of the performance, two step time-to-digital converter is selected as the research object. In this paper, a 10 bit time-to-digital converter has been designed based on pulsed counter and delay line structure. The TDC works in 285 MHz reference clock frequency, has a 219 ps time resolution and 112 ns dynamic range, the differential nonlinearity(DNL) and integral nonlinearity error(INL) were ± 0.52 LSB and ± 0.8 LSB, timing offset error is less than 3.5%.At the same time, based on the two step time-to-digital converter, the pixel readout circuit of the three-dimensional imaging sensor is designed. Using avalanche photodiode as a photon detector, in addition to the most important module time-to-digital converter, pixel readout circuit also includes front-end circuit, interface circuit and other circuit sub units. The pixel area is 110 μm2, has a frame rate of 1.5 MHz.Finally, the array design and layout of the pixel array is done, the array size is 16 ×16, the array area is 2000 μm×2300 μm.