Zhe Zhao (a), Xiufeng Weng (b), Shiquan Fan (a), Ruiqi Min (a), Yang Li (a), Xiao Liu (b), Xinjian Tan (b), Zhongliang Li (a) (c), Guohe Zhang (a)
(a) School of Microelectronics, Xi’an Jiaotong University, Xi’an, 710049, China
(b) Northwest Institute of Nuclear Technology, Xi’an, 710024, China
(c) Shaanxi QinZhou Nuclear and Radiation Safety Technology Co, Xi’an, 710000, China
## Abstract
This paper presents a High-Speed Electronics System with Timing and Amplitude Signal Acquisition Design for Multi-channel
Cadmium Zinc Telluride (CdZnTe) Array Detector. The readout channel comprises preamplifiers, post-amplification stages, peak hold and detection circuits, a multiplexer, an analog-to-digital converter (ADC), time-to-digital converters (TDC), and calibration circuits. In circuit design, a differential voltage amplifier (DVA) is used as the preamplifier in order to achieve similar performance to that of the Charge Sensitive Amplifier (CSA) while decreasing the design cost and complexity, and the peak hold circuit employs a Schottky diode with RC to achieve a high signal throughput. The results of the tests demonstrate that the typical signal output from the CdZnTe detector is within 10 ns of the rising edge after amplification and has a signal throughput rate of 1 MCPS. The system was irradiated using an X-ray Generator with a pulse width of 50 ns, and the resulting 9-channel envelope half-width is at 40.5 ns, which is in line with the actual pulse width.
## Introduction
CdZnTe semiconductors are regarded as potentially valuable materials [1] for the construction of X-ray and gamma-ray detectors due to their superior properties in low-intensity radiation detection areas [2], [3]. In comparison to the challenges presented by the poor resolution of gas detectors and the long response time of scintillation detectors, such as NaI, CsI, and MHPs, CdZnTe detectors offer distinct advantages [4]. CdZnTe detectors are capable of operating at room temperature while delivering excellent energy resolution and a fast response time [5]. These characteristics make CdZnTe an ideal material for use in array detection [6]. In order to effectively process data, the amplifying ability and time response speed of the backend electronic components must be exceptionally high [7], [8].
However, the acquisition of the output signal from a CdZnTe detector currently presents some difficulties. Firstly, when a CdZnTe detects radiation signals, the current magnitude typically ranges from a few nA to occasionally even pA levels, which makes it susceptible to being overwhelmed by noise [1], [4]. Furthermore, the rising edge of the signal generated by the radiation event is typically very short, ranging from 380 ps to 10 ns [9], [10], [11]. During the amplification process, the signal is highly susceptible to distortion, and the demand for the sampling rate of the analog-to-digital converter (ADC) is considerable. In the context of radiometry, the timing of the signal corresponds to the occurrence of a radiation event, while the signal amplitude represents the magnitude of the radiation. These two aspects constitute the key information of the radiation signal. In order to reduce the sampling rate requirement, only the timing and amplitude of the radiation signal are selected for acquisition, with the overall waveform of the signal being excluded. Meanwhile, the use of multiple samplers working simultaneously enables the high-speed signal to be divided into different time axes, thus enabling the conversion of high-speed signals.
A commonly used amplifier circuit for spectrum capture of CdZnTe detector is usually based mainly on the Charge Sensitive Amplifier (CSA) [12], [13], [14], [15], [16], [17], [18]. This is because the CSA provides better signal fidelity and sensitivity, offering satisfying signal gain and signal-to-noise ratio (SNR). Amplification systems using a CSA have a signal rising edge in the range of 195 ns to 10us [19]. The accompanying limitations are relatively complex circuit designs, particularly with regard to challenges such as parasitic capacitance, CdZnTe crystal purity, and amplifier shielding. Thus, CSAs are suitable and typically applied for high-precision capture of the full signal waveform and spectrum capture. In our design, we focused on capturing the full-band signal while maintaining adequate SNR. To simplify the design, this paper chooses a DVA and focuses only on capturing the signal amplitude and timing.
Additionally, many previous efforts have been made to address the challenges in acquiring the timing and amplitude of high-speed pulse signals. For the amplitude acquisition component, the signal is usually slowed down overall by slow shaping, and then the signal amplitude is acquired using a low-speed ADC [19]. This method can result in a slowing of the rising edge of the signal, which may lead to the inability to capture the peak time of the signal and also greatly reduce the pass rate of the signal. Due to the excellent high-frequency performance of Schottky diodes, the use of a Schottky diode as a peak hold circuit enables the signal to be held at a peak without affecting the rising edge of the signal.
For the time acquisition of multichannel signals, corresponding the peak moment with the amplitude is also a major challenge. A high-speed comparator is employed to output an enable signal of the peak moment, which is then captured by a TDC. To ensure the accuracy of the captured peak, the TDC is calibrated on a regular basis.
This paper presents the structure and performance of 9-channel High-speed Signal Timing and Amplitude Acquisition Electronics System. Section 2 introduces the structure of the system and the details of the circuit. Section 3 gives the test results with a 3 × 3 array CdZnTe detector. Section 4 concludes the paper.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/thesis/high-speed-electronics-system-with-timing-and-amplitude-signal-acquisition-design-for-multi-channel-cdznte-array-detector.html