Parasitic capacitances can cause demodulation RFI to differ in inverting and noninverting operational amplifier circuits

IEEE 1991 International Symposium on Electromagnetic Compatibility Pub Date : 1991-08-12 DOI:10.1109/ISEMC.1991.148203

H. Ghadamabadi, J. Whalen

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引用次数: 1

Abstract

The demodulation RFI responses of an inverting operational amplifier (op amp) circuit and a noninverting op amp circuit are compared. The intended voltage gain of the inverting op amp circuit is A/sub 1/=-R2/R1=-10. The intended linear voltage gain of the noninverting op amp circuit is A/sub N1/=(R1+R2)/R1=11. For both circuits, the resistor values are R1=10 k Omega and R2=100 k Omega . Analysis shows that parasitic capacitances C/sub in/ (between the inverting and noninverting inputs of the op amp) and CR1 (shunted across R1) cause the inverting op amp circuit to have better RFI immunity than the noninverting op amp circuit. The derivation is based on the hypothesis that the demodulation RFI response is caused by a second-order nonlinearity so that a 3-dB reduction in the linear voltage gain causes the second-order demodulation RFI response characterized by the transfer function H/sub 2/ to be reduced by 6 dB. For the assumed values of C/sub in/=8 pF and CR1=0.4 pF. the measured and calculated values of the difference between H/sub 2/ values for the inverting and noninverting circuits were in good agreement.<>

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寄生电容会导致反相和非反相运算放大器电路中的解调RFI不同

比较了反相运算放大器(运放)电路和非反相运放电路的解调RFI响应。反相运放电路的预期电压增益为A/sub 1/=-R2/R1=-10。非反相运放电路的预期线性电压增益为A/sub N1/=(R1+R2)/R1=11。对于这两种电路，电阻值分别为R1= 10k ω和R2= 100k ω。分析表明，寄生电容C/sub /(在运放的反相输入和非反相输入之间)和CR1(分流穿过R1)使得反相运放电路比非反相运放电路具有更好的RFI抗扰性。该推导基于这样一个假设，即解调RFI响应是由二阶非线性引起的，因此线性电压增益降低3db会导致以传递函数H/sub 2/为特征的二阶解调RFI响应降低6db。对于C/sub in/= 8pf和CR1=0.4 pF的假设值，反相电路和非反相电路的H/sub 2/值之差的实测值和计算值符合得很好。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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IEEE 1991 International Symposium on Electromagnetic Compatibility

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