Research On Single Photon Counting Chip Based On Time Amplitude Conversion

Time-correlated single photon counting(TCSPC)system has very high sensitivity and linear dynamic range.Because of this,it has been more and more widely used in fluorescence lifetime detection,laser ranging,diffusion optical tomography and other applications.TCSPC technology is aimed at the detection of weak photoelectric signals.Its work is mainly to process the time interval between the periodic laser beam working at high frequencies and the fluorescent photons excited by the laser beam,and to quickly record and construct a time photon histogram through corresponding processing,which directly reflects the change of the probability of fluorescence photon emission with excitation time.The key instruments in the single photon counting system are mainly high frequency excitation sources,single photon detectors,time measurement modules,and multi-channel pulse height analyzer(MCA).How to improve the time resolution,measurement accuracy and transmission speed of the TCSPC system is still a hot topic of current research.Based on the research background of fluorescence lifetime detection,the design and analysis of the TCSPC system are studied in this paper.According to the design requirements of measurement accuracy,time resolution and transmission speed,the internal unit modules of the TCSPC system were analyzed and designed.The main research work is as follows:1. In order to reduce the impact of timing jitter caused by amplitude jitter,a constant fraction discriminator(CFD)circuit combining a rising edge discriminator and a zero-crossing level adjustment circuit is designed in this paper.The positive emitter-coupled logic(PECL)circuit and true single-phase clock(TSPC)D flip-flops are analyzed and optimized accordingly.When the zero-crossing level is set to 0.2V,the time walk achieved by the CFD circuit reaches6.19ps.2. In order to achieve higher time resolution and conversion speed,this paper designs a time measurement module that combines time-to-amplitude converter(TAC)and analog-to-digital converter(ADC).Among them,the TAC circuit is mainly composed of a bandgap reference source,a V-I conversion circuit,a differential operational amplifier circuit,and a fully differential operational amplifier circuit.The ADC uses a 12-bit successive approximation(SAR)structure with low power consumption,medium accuracy and medium conversion speed.This article first optimized the bandgap reference circuit to achieve a lower temperature coefficient and a higher power-supply voltage rejection ratio(PSRR),which provided reliability for the constant current design.Then optimized the two operational amplifiers,it achieves a higher DC gain,bandwidth and slew rate,which ensures the conversion accuracy and response speed of the TAC circuit.Finally,the 12-bit SAR ADC is optimized to achieve higher conversion accuracy and speed.3. The design of TCSPC system was completed by using Cadence simulation software.Under the power supply voltage of 3.3V and operating frequency of 2MHz,the time resolution of the time measurement module reached 31.8ps,the conversion error achieved by the single photon counting system was 1.412m V,and the overall power consumption was 142.7m W.Finally,based on the Korean Dong Bu Hi Tek 0.18μm 1P4M BCD process,the layout and tape-out of the TCSPC system were completed,and the overall layout area was 1680?1700μm~2.