Research And Design Of Analog Channel For 5GHz Oscilloscope

The bandwidth of oscilloscope analog channel is always the key index that restricts the bandwidth measured by oscilloscope.In this paper,by selecting appropriate electronic devices,discrete devices are used to build oscilloscope analog channel circuit.The analog channel bandwidth of DC~5GHz oscilloscope is realized by combining theoretical analysis and simulation analysis,optimize the circuit and PCB design.The thesis mainly studies the following contents.1.Discrete devices are used to build variable gain amplification circuit and impedance conversion circuit.A feedback compensation network is designed for the input frequency response of ADC,which makes up for the ADC input bandwidth shortage and makes the-3dB bandwidth of the signal conditioning channel reach 5GHz.2.The broadband impedance conversion circuit is deeply studied.By comparing different circuit schemes,the load driving ability and bias adjusting ability of which are analyzed theoretically.The effects of PCB layout,copper laying and wiring on highfrequency signals are studied.The schematic diagram and PCB layout simulation of impedance transformation circuit are carried out to realize the broadband impedance transformation circuit with a bandwidth of over 5GHz.3.Based on the theoretical analysis and modeling of the noise of cascaded operational amplifier,a low noise gain regulation circuit is designed.The relationship between insertion loss,common mode rejection ratio and power rejection ratio and noise is analyzed.The structure of amplifying circuit and bandwidth limiting circuit are optimized to reduce the channel noise.4.Broadband trigger channel is designed.The selection circuit of multi-channel trigger source,comparison level regulation circuit,hysteresis voltage regulation circuit and trigger frequency division circuit are mainly studied in this paper and the trigger sensitivity can be programmed and adjusted.5.Channel control circuit is designed.Multiple shift registers are cascaded and serial input is converted to parallel output to realize multi-state switching of channel analog by oscilloscope.The working characteristics of different control switches and the realization of control circuits are analyzed.The feasibility of distributed power supply scheme is studied,and the PCB design of power supply circuit is analyzed from the perspective of power integrity.In order to facilitate debugging and improve testing efficiency,this paper designed a debugging platform specifically for the analog channel of oscilloscope.With the help of vector network analyzer,oscilloscope,calibration instrument and other test instruments as well as channel control platform,the bandwidth,rising time,bias range,input resistance and capacitance and other indicators of analog channel have been tested and verified.All test results meet the index requirements.