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一、一般原理前置放大器的后级噪声,指其负载电阻的过剩噪声和电源的纹波及干扰等。通常是被忽略的,但当所放大的信号频率较低,且很弱时,后级噪声源就不容忽视。以下对结型场效应管的前置放大器进行简要讨论。1.负载电阻的影响:负载电阻中的过剩噪声为1/f噪声,在低频端迅速增大,一般用电阻做负载的前置放大器,增益约在10～10~2数量级,如选用噪声指数为-20分贝的金属膜电阻做负载,10伏压降下的过剩噪声[1]在10赫时为210毫微伏、100赫时为66毫微伏、1000赫时为21毫微伏。折合到输入端,分别为2～21毫微伏、0.66～6.6毫微伏、0.2～2毫
First, the general principle Post-amplifier noise after the stage, refers to the excess load noise and power supply ripple and interference. Usually ignored, but when the amplified signal frequency is low, and very weak, the latter class of noise sources can not be ignored. The following is a brief discussion of the JFET’s preamplifier. 1, the impact of load resistance: the load resistance of the excess noise 1 / f noise, rapidly increasing at the low-frequency, the general load resistance with a preamplifier, gain of about 10 ~ 10 ~ 2 orders of magnitude, such as the selection of noise figure It is loaded with a metal film resistor of -20 dB and the excess noise at 10 V drop is 210 nV at 10 Hz, 66 nV at 100 Hz and 21 nV at 1000 Hz. Equivalent to the input, respectively, 2 ~ 21 nm, 0.66 ~ 6.6 nm, 0.2 ~ 2 milliliters