Tham khảo tài liệu 'biomedical engineering trends in electronics communications and software part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 310 Biomedical Engineering Trends in Electronics Communications and Software Fig. 15. Time amplifier. a Schematic of a time amplifier b Conception of the time amplifier c Characteristic of the time amplifier. TDC based on time amplifier It is a big challenge to measure the time interval with picoseconds-level resolution. The reason is that the performances of TDCs are mainly determined by the finite SNR and the mismatch of integrated elements. The conception of the time amplification is an effective solution for this issue. The schematic of a time amplifier TA which was proposed in Lee Abidi 2007 is shown in Figure 15 a . The operation is similar with an voltage amplifer. The difference is that the TA processes a tiny time difference and outputs a larger time difference. The conception of the TA is shown in Figure 15 b . However the circuit techniques of the TA is under developed. The state-of-the-art of the time amplifiers only can process a finite range of time interval. As shown in Figure 15 c the transfer characteristics of the TA is not linear. Thus the use of a TA should be based on the test results in the present age. However the idea of time amplification gives a new research direction of TDC techniques which needs to be optimized in the future work. The architecture of a TA-based TDC is illustrated in Figure 16. The function of a time amplifier is simular to the preamplifier in the front-end electronics. In the neighborhood of the center point the gain of the TA is monotone increasing thus the behaviour of the TA is given as Tout Kta Tin 22 where Tin and Tout are the input and output time interval respectively. Kta is the gain of the TA. Since Kta is not linear a calibration circuit is required. The TDC core could be a Integrated High-Resolution Multi-Channel Time-to-Digital Converters TDCs for PET Imaging 311 Fig. 16. Architecture of TDCs based on a time amplifier. The function of a time amplifier is simular to the preamplifier in the front-end .
