Design of a Low-Noise Front-End Readout CSP-Shaper System for CZT Detectors

Huiming Zeng, Tingcun Wei, Bo Gan, Wu Gao

School of Computer Science and Technology, Northwestern Polytechnical University, Xi’an, China.

DOI: 10.4236/jsip.2013.42016                

Abstract

This paper describes a low-noise front-end readout circuit for CZT detectors based on TSMC 0.35 um mixed-single CMOS technology; mainly analyzes the noise model of the detector-preamplifier and presents the low-noise circuit schematic of charge sensitive preamplifier and shaper. Considering the parasitical influences, the circuit and layout-design are optimized to reduce noise. The preliminary simulation results show that, the equivalent noise charge (ENC) is 74 e^﹣ (rms), noise slope is 9 e^﹣/pF, power consumption is 2 mW, and non-linearity is <3%.

Keywords

CZTdetector; Front-End Readout; CSP; Low-Noise

1. Introduction

Cadmium Zinc Telluride (CZT or CdZnTe) has recently captured most considerable attention as the radiation material due to their relatively high atomic number (Cd: 48, Zn: 30, and Te: 52), high density (≈5.9 g/cm³) and wide band gap tuned by changing the elements decomposition (≈1.5 - 2.2 eV) [1]. The ability to operate in direct-conversion mode at room temperature and high resolution make CZT detectors an excellent choice for instrument miniaturization, moreover, the CZT detectors are widely used in industry, medicine, antiterrorism, nuclear security, astrophysics, aerography, space research, etc. [2,3]; as well be applied for radiation synchrotron beam control and equipment chemical corps. In 1980s, the development and breakthrough of the Cadmium Zinc Telluride growth technology make producing large-area and high-performance CZT detectors a possibility.

Since the CZT detectors become welcome among semiconductor detectors, the design of front-end readout circuitis is necessary to detect the weak signals of CZT detectors [4,5]. Firstly, we propose the circuit structure based on TSMC 0.35 um mixed-signal CMOS technology due to the requirement of low-noise; secondly, we discuss noise analysis of the circuit structure, mainly analyze the noise model of detector and preamplifier; thirdly, we design the low-noise circuit topology and layout, and simulate all the circuits considering the parasitical parameters. The simulation results show that, the circuit system can satisfy the low-noise front-end readout requirements of weak signals from CZT detectors.

2. System Structure

Figure 1 shows the low-noise front-end readout circuit structure for CZT detectors proposed in this paper. The system mainly includes two parts: preamplifier and shaper. The change of the temperature and bias voltage of CZT detectors can cause a change of the semiconductor junction capacitance C_d, and lead to the output voltage signal amplitude instable, thus it is difficult to measure the energy spectrum. In order to solve this problem, a charge sensitive preamplifier (CSP) is needed to convert charge to voltage (Q→V). The CSP consists of Miller integrator preamplifier with stable output voltage amplitude and higher signal to noise ratio.

Conflicts of Interest

The authors declare no conflicts of interest.

References

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