A high-dynamic-range counting−analog detector system based on a secondary electron multiplier (SEM) is described. The current-to-voltage converter, which is common to both channels, includes a high-speed transimpedance amplifier (TIA) and an automatic bias-correction circuit. This circuit also rejects 1/ f noise of the TIA in the 0−2.3 Hz passband of the digital lowpass filter of a 24-bit analog-to-digital converter (ADC) in the electrometric channel. As a result, the noise-free code resolution of the entire channel, which is 18.5 bits, is determined only by the ADC noise. A number of circuit solutions are proposed to minimize the number of circuit components, which have made it possible to place the detector system board in the measuring head of the SEM and thereby reduce the stray capacitances that limit the response speed of the TIA. The maximum counting rate of the pulse-counting channel is 7 ×10⁷ cps and is determined by the time resolution of the SEM. The problems of optimizing the supply voltages of the circuit and the gain of the SEM in the counting−analog mode are considered. The developed system is one of the units of the mass-spectrometry system for the isotope study of noble gases. The SEM-input-referred measurement ranges of the system are as follows: from 1 × 10^–16 to 1.2 × 10⁻¹¹ A at a resolution of 3 × 10⁻¹⁷ A or better for the electrometric channel; from 5 × 10⁻² to 5 × 10⁷ ions/s for the pulse-counting channel without counting losses and with the allowance for the SEM dark current; and from 1 × 10^–20 to 1.2 × 10⁻¹¹ A for the entire system. Due to the wide overlap of the measurement ranges, it is possible to perform mutual verification of data obtained in different modes.

中文翻译：

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基于二次电子倍增器的高动态范围计数模拟检测器系统

描述了基于二次电子倍增器（SEM）的高动态范围计数模拟检测器系统。这两个通道共用的电流电压转换器包括一个高速跨阻放大器（TIA）和一个自动偏置校正电路。该电路也拒绝1 / f 电测通道中24位模数转换器（ADC）的数字低通滤波器的0-2.3 Hz通带中的TIA噪声。结果，整个通道的无噪声代码分辨率（18.5位）仅由ADC噪声决定。提出了许多电路解决方案以最小化电路组件的数量，这使得可以将检测器系统板放置在SEM的测量头中，从而减少限制TIA响应速度的杂散电容。脉冲计数通道的最大计数率为7×10 ⁷cps，由SEM的时间分辨率确定。考虑了在计数模拟模式下优化电路的电源电压和SEM增益的问题。研发的系统是用于稀有气体同位素研究的质谱系统的单位之一。该系统以SEM输入为参考的测量范围如下：对于电测通道，分辨率为3×10 ^-17 A或更高，从1×10 ^–16到1.2×10 ^-11 A ；对于脉冲计数通道，从5×10 ^-2到5×10 ⁷ ions / s，不计损耗，并且允许SEM暗电流；从1×10 ^–20到1.2×10 ^-11用于整个系统。由于测量范围的广泛重叠，因此可以对以不同模式获得的数据进行相互验证。