Research And Design Of 1GHz Wideband Low Noise Analog Channel

With the increase of wideband weak small signal,switching power supply testing,signal integrity and other areas of test application requirements,LeCroy,Keysight and other foreign companies have released high-resolution oscilloscopes,while domestic companies have less related research.High-resolution oscilloscopes are able to observe more accurate and precise waveforms,and low-noise analog front ends are an important part of high-resolution oscilloscopes.This paper chooses wideband low-noise analog channel as the research topic.This paper mainly focuses on the technology of wideband impedance conversion circuit,low-noise variable gain amplifier,differential ADC driver and wideband trigger circuit.The research is devided into five parts:1.Research and design of a kind of impedance conversion circuit based on high and low frequency separation.Analyzing the principle and structure of the circuit and the transfer function of the circuit is given.The factors influencing the high frequency gain of the circuit are analyzed.The actual circuit is built by discrete devices such as field effect transistor,transistor and op amp and the circuit is simulated by software.At last the bias-voltage adjustment circuit based on the impedance conversion circuit is designed.2.The noise of the cascade amplifier is studied,including the common op amp noise type,the amplifier amplifier noise model,and cascade amplifier noise calculation methods.3.Research and design of broadband low noise variable gain amplifier circuit.The gain and attenuation range of the circuit are analyzed,and the cascade structure of the programmable attenuator + fixed gain op amp + fully differential op amp drive circuit is established.The specific circuit is designed by selected chips,and the circuit noise is analyzed and calculated.4.The gain temperature stability of the signal conditioning channel is analyzed,and the temperature compensation method based on ADC gain adjustment is given.5.The study designs a wideband trigger conditioning channel.The principle structure of triggering is analyzed,and edge triggering circuit,frequency dividing circuit and trigger coupling control circuit are designed.Finally,the design of the 1GHz oscilloscope analog channel is debugged and verified at 2.5GSPS sampling rate,12-bit vertical resolution oscilloscope platform.The channel bandwidth,rise time,noise index,and other key indicators can meet the design requirements.