Automatic Offset Cancellation and Time-Constant Reduction in Charge-Sensitive Preamplifiers
Automatic Offset Cancellation and Time-Constant Reduction in Charge-Sensitive Preamplifiers
复制标题
DOI：
10.1109/tns.2009.2038913
复制
发表时间：
2010-02
影响因子：
1.8
通讯作者：
A. Pullia;F. Zocca
中科院分区：
文献类型：
--
作者：
A. Pullia;F. Zocca
提出了一种消除电荷敏感前置放大器输出端失调的电路技术，并有选择地减小了电阻复位时间常数。偏移消除以及时间常数的减少获得没有修剪。通过负反馈路径主动获得偏移消除，负反馈路径的误差变量是偏移本身。因此，输出电压偏移被自动消除，而与输入晶体管的偏置点和连接到三极管的传感器的暗电流无关。在锗探测器的低噪声电荷前置放大器中使用所提出的技术，在100-300 mV范围内的典型偏移被减小到±2 mV。失调消除电路不影响ADC的噪声。此外，通过在所提出的电路中插入可选的电阻器，可以自动地将电荷泵的衰减时间常数减小多达10倍，同时保持电荷泵的噪声和灵敏度不变。这改善了在MEMS输出端的脉冲分离，这对于高事件率下的模式识别特别有用。实现的无失调电路在3 º s整形时间时在锗中具有650 eV fwhm的等效噪声，即~ 94个电子r.m.s.的等效噪声电荷动态范围超过86 dB，非常适合使用大型锗探测器的高分辨率伽马射线光谱测量。
A circuit technique is presented which eliminates the offset at the output of charge-sensitive preamplifiers and optionally reduces the resistive reset time-constant. Offset cancellation as well as time-constant reduction are obtained with no trimming. Offset cancellation is obtained actively through a negative feedback path whose ¿error¿ variable is the offset itself. As a result the output voltage offset is automatically eliminated, irrespective of the bias point of the input transistor and the dark current of the sensor connected to the preamplifier. Using the proposed technique in low-noise charge preamplifiers for germanium detectors typical offsets in the range 100-300 mV are reduced to ±2 mV. The noise of the preamplifier is unaffected by the offset cancellation circuit. Moreover, by insertion of an optional resistor in the proposed circuitry the decay time-constant of the preamplifier is automatically reduced by a factor of up to 10, while leaving unchanged the noise and the sensitivity of the charge preamplifier. This improves pulse separation at the preamplifier's output, which can be particularly useful for pattern recognition at high event rates. The realized offset-free circuit features an equivalent noise of 650 eV fwhm in germanium at 3 ¿s shaping time, i.e. an Equivalent Noise Charge of ~ 94 electrons r.m.s. and a dynamic range in excess of 86 dB, which makes it perfectly suited for high-resolution gamma-ray spectrometry with large germanium detectors.