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像素探测器[1]是当前最先进的位置灵敏探测器之一,在加速器物理实验的内径迹探测系统[2]、X光成像[3]等领域都有着广泛的应用。像素探测器由于通道密度高,给读出电子学的设计带来很大的挑战,其信号读出采用ASIC(Application Specific Integrated Circuit) 芯片实现。典型的ASIC芯片,如Timepix系列芯片[4-5]、Medipix系列芯片[6-7]、Topmetal系列芯片[8]均在相应的领域有着重要的应用。
像素阵列读出芯片通常由一个个单像素电子学组成的阵列及其控制逻辑组成,通常具有像素数目多、单像素面积小的特点。例如,Topmetal-Ⅰ芯片单个像素尺寸为80 μm×80 μm,像素阵列大小为64行×64列;Medipix-Ⅱ芯片单个像素尺寸为55 μm×55 μm,像素阵列大小为256行×256列;Timepix系列芯片单个像素尺寸为55 μm×55 μm,像素阵列大小为256行×256列。通过像素阵列的每一个击中信号的信息都会被记录下来,通常因为应用场景的不同而设计为在不同的模式下工作具备不同的功能。值得注意的是,Timepix3芯片[5]可以在三种模式下工作:光子计数模式、TOA(Time-over-Arrival)[9-11]和TOT(Time-over-Threshold) [12-13],同时具备位置分辨、时间测量及能量测量的能力,其中bin size可以达到1.56 ns。随着物理实验和其他应用场景的发展,对时间测量的精度提出了更高的要求,需要设计性能更加优越的TDC(Time-to-Digital Conversion) ASIC来满足需求。
预期未来像素阵列设计的规模为100行×100列,本文设计的TDC负责单列信号的时间信息测量,即未来需要100通道TDC集成到像素阵列的末端,本设计为验证TDC性能,设计为两通道。考虑到一列100个像素点可能存在多个像素点被击中的情况,因此预期一列像素的输出信号具备以下特点:输出信号为连续脉冲信号,相邻脉冲信号时间间隔最短为500 ps,脉冲宽度最短为200 ps,连续的脉冲信号最多包含十个连续脉冲。要求测量每个脉冲的前沿和后沿的到达时间,bin size达到10 ps,精度好于10 ps RMS。
设计的难点在于如何在有限的40 μm宽度(单个像素预期尺寸为40 μm×40 μm)范围内处理高速的多事例信号,并同时获得高的时间测量精度。将指标需求总结为表1。
指标 TDC 精度 优于10 ps RMS bin size 优于10 ps 速度 2 GHz(最多处理10个信号)
Design and Simulation of High Event Rate and High Precision TDC ASIC Prototype for Pixel Detector
doi: 10.11804/NuclPhysRev.39.2021027
- Received Date: 2021-03-08
- Rev Recd Date: 2021-04-21
- Available Online: 2022-06-29
- Publish Date: 2022-06-29
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Key words:
- pixel detector /
- high event rate /
- high precision /
- TDC /
- ASIC
Abstract: The pixel detector has been widely used in the inner track detector of high energy particle physics experiments because of its excellent position resolution. With the development of physics experiments, many experiments require detectors and readout electronics to have the capability of high-precision time measurement. To reach the requirement of pixel detectors about the time measurement, a TDC(Time-to-Digital Conversion) ASIC(Application Specific Integrated Circuit) prototype with high event rate processing capability and high precision has been designed. It is expected to be integrated with the front-end readout ASIC of pixel detector as a core component in the future. TDC presented in this paper adopts the combination of coarse and fine measurement, in which the coarse time measurement is based on the counter, and the fine time measurement is implemented by employing the architecture of TAC(Time-to-Amplifier Converter) combined with ADC(Analog-to-Digital Converter). The prototype circuit has been designed based on 130 nm process. TDC has also been simulated, the simulation results indicate that the circuit has the capability processing up to 11 consecutive events in which the time interval between adjacent events is as small as 500 ps, while the bin size of TDC is 2 ps, the DNL (Differential Non-Linearity) is less than 2.8 ps, and the time measurement precision is better than 5 ps RMS.
Citation: | Zijian LANG, Chaosong GAO, Jiajun QIN, Lei ZHAO, Xiangming SUN, Qi AN. Design and Simulation of High Event Rate and High Precision TDC ASIC Prototype for Pixel Detector[J]. Nuclear Physics Review, 2022, 39(2): 206-214. doi: 10.11804/NuclPhysRev.39.2021027 |