| Broadband signal conditioning channel is a very important part in the research of modern high-speed digital oscilloscope,which determines the bandwidth,dynamic range,rise time and other key indicators of oscilloscope.In order to realize 10 GHz signal conditioning channel,this thesis focuses on the study of DC-coupled broadband variable gain circuit,broadband impedance conversion circuit,broadband ADC driver circuit,also using simulation software to study the layout of high frequency PCB and the overall cavity shielding system.The main research contents include:1.Research on broadband variable gain circuit.A circuit which can compensate for gains is designed to solve the uneven gain problem of differential RF amplifier.For the requirements of different gain adjustment ranges,broadband amplifier,broadband attenuator and broadband analog switch are used to design and realize the broadband amplifier circuit with variable gain of-22 d B~18 d B.2.Research on broadband impedance conversion circuit.Through modeling and simulating of the traditional impedance conversion circuit which based on discrete broadband transistors,the results show that the-3 d B bandwidth of the scheme is only up to 8.4 GHz,which cannot meet the demand of signal conditioning channels with higher bandwidth.According to the external characteristics of the impedance transformation,analyzing the circuit principle of the broadband amplifier,and the input bias current is compensated to solve the problem of input impedance instability.Finally,the broadband amplifier scheme is used to realize the broadband impedance conversion function.3.Research on broadband ADC driver Circuit.Compare the pros and cons of common multi-channel drive schemes and select the integrated chip to complete the wideband drive circuit design.To solve the problem of mismatch between analog splitter output common-mode voltage and ADC input common-mode voltage,a common-mode voltage regulating circuit is designed to realize the two pairs of differential output signalswith good consistency.4.Study on broadband signal conditioning channel layout routing.By studying the theory of high frequency PCB and designing the reasonable layout routing with CST,the problem of the transmission line loss and the impedance discontinuity between microwave connector and PCB connection are solved.This design optimize the overall frequency response of the system.The channel layout routing design guidelines are formed and the PCB of channel is completed.5.Study on electromagnetic shielding of broadband signal conditioning Channel.Relevant theories of electromagnetic interference are studied,and a reasonable channel shielding cavity is designed based on CST,which successfully solves the problems of cavity resonance and cross-talk between channels during electromagnetic shielding.Finally,through the test verification,the signal conditioning channel can meet the DC-10 GHz bandwidth,rise time 40 ps,gain adjustable range of-22 d B~18 d B,the isolation between channels can reach 104 d B,meeting the system design requirements. |
