Research And Design Of The Active?High Voltage?Differential Oscilloscope Probe

In the ordinary when we observe the power supply,inverter circuit waveform and other strong signal waveform with an oscilloscope,if we use conventional passive oscilloscope probe will cause many problems,to avoid the problems,you can use high voltage differential probe,because the two input of the differential probe don't have the problem of grounding,it can convert floating differential signal in pairs of a low voltage signal,to avoid some of the dangerous phenomenon previously described passive probe may arise.This design of high-voltage differential probe based on the principle of differential amplifier circuit,differential amplification principle refers to a pair of signal input to the amplifier circuit and the original signal is obtained by subtraction,It is a differential amplifier by the same two parameters characteristic of transistors,as a result of the integration differential amplifier circuit input impedance is too low,unable to realize the front-end electrical isolation between high voltage signal with low voltage signal,it must be added to an impedance transformation circuit between the front and rear differential amplifier input to improve its input resistance to achieve the purpose of electrical isolation,in this paper,i do a lot of signal isolation test by optocoupler?transformer?integrated signal isolating devices and so on.Found that low frequency signal isolation effect is also acceptable,high frequency signal transmission distortion is serious,After many trials finally decided JFET type differential amplifier circuit is used to do the middle level,JFET is characteristic of low noise,high input impedance,low consumption,allows the limits of the high frequency.According to the principles and requirements,I set up the hardware test platform,circuit module mainly includes four parts,high voltage resistance and capacitance bleeder circuit,JFET differential amplification circuit differential output into single-ended output circuit and the proportion of the power supply,the thesis introduces the related circuit design,simulation,testing and troubleshooting and so on.After at the end of the paper describes the improvement work,especially in the measurement of precision test and how to further improve the signal frequency.