高灵敏测量放大器研制

The Resarch of A Supersensitive Measuring Amplifier

高灵敏测量放大器由信号输入变压器,前置放大器,高Q 选频带通滤波器和线性检波器组成在20dB 输出信号噪声比条件下,整机灵敏度高达0.1μV,比FD-1测量放大器高二个量级,前置放大器输入级采用低噪声场效应晶体管,其等效输入噪声电压为7 nV/(Hz)^(1/2)。选频带通滤波器为一态变量有源滤波器,其频率范围从10Hz 到5 kHz,幅度精度为±5%,线性检波电路由运算放大器构成,在40dB 动态范围内,线性度优于2%。文中讨论了信号输入变压器线电阻对噪声的影响。

The supersensitive measuring amplifler consists of signalinput transformer,preamplifier,high Q selective bandpass filter and lineardetector.In the condition of 20dB output SNR,the sensitivity of the unitreaches 0.1μV improving a two decade range on model FD-1 measurementamplifier.The input stage of preamplifier uses the low noise JFET.Itseguivalent input noise voltage is about 7nV/(Hz)^(1/2).The selective bandpassfilter is a state variable active filter.The freauency range responds 10Hzto 5kHz and the amplitude accuracy is ±5%.The linear detected circu-it with operational amplifier is 40dB dynamic range and its linearity is2%.The noise voltage contributed by the wire resistance of raisingsignal tramsformer is discussed also.