核医学仪器科学中的电路仿真

目的：核电子学可应用到核医学诊断领域,为核医学研究提供硬件支持。提高核仪器的电路性能可从根本上促进核医学的发展。借助电路仿真,本文研究核电子学中一个重要的基本部件,电荷灵敏前置放大器。该前置放大器在高分辨率能谱测量系统中有着广泛的应用。方法：我们利用Pspice,orCAD电路仿真软件,对电荷灵敏前置放大器的基本电路,进行了温度效应、噪声效应和其他主要性能指标的仿真分析,并与理论值进行了比较。通过调节电路参数,可动态观察输出结果如输出电压波形,并可形象地观察工作温度的变化对输出信号和输出噪声的影响,从而了解电路指标的温度效应。结果：对变换增益和平均计数率等主要电路参数的仿真结果和理论一致。泄放电阻的使用可以释放累加的电荷信号,使放大器工作在线性范围。分布电容是产生前置放大器噪声的主要原因,减小噪声必须减小分布电容。输出噪声在正常的工作频率范围内,会随温度增加而增大。结论：在高分辨率能谱分析仪设计中,使探测器和前置放大器系统的信噪比最大化是至关重要的。充分考虑电路的温度和噪声等效应是设计高性能前置放大器的基础,有助设计低噪声的前置放大器。电路仿真具有实现快、输出结果形象、可将如噪声效应抽离进行分析等特点,在核电子学以及医学仪器设计方面有广泛的应用空间。

Nuclear Instrumental Circuit Simulation in Nuclear Medicine

Objective: Nuclear electronics can be applied to nuclear medicine diagnosis,providing hardware support for research in nuclear medicine.Improvement in nuclear instruments may radically facilitate the development of nuclear medicine.This work studies a basic element in nuclear electronics by circuit simulation,the charge-sensitive preamplifier,which has been widely employed in high resolution nuclear energy spectrometers.Methods: We employ EDA software such as orCAD and Pspice to simulate charge-sensitive preamplifier circuits for implementing transient analysis,noise analysis and temperature analysis.Simulation results show convincing agreement with theory.By varying circuital parameters,the output such as voltage output waveform can be observed dynamically.The output signal and noise response to working temperature changes can also be observed vividly in order to study the circuit temperature effect.Results: Primary circuital parameters including conversion gain and mean count rate agree well with theory.Leak resistance is required in order to maintain the normal work linear range by releasing accumulated charges.The distributed capacitance is the main source causing noise in preamplifier,which must be reduced to minimize noise.Output noise level will increase as a response to the rising temperature within the normal working frequency range.Conclusions: Maximizing the signal to noise ratio of detector and preamplifier is critical to the design of high resolution energy spectrometer.Care must be taken to study temperature and noise effect for designing low noise high quality preamplifier.Circuit simulation has advantages such as fast operation,observable vivid output,and the ability to separation of noise from the signal,which should be found great potential of use in designing nuclear electronics and medical instruments.