The Design And Implementation Of Vector Signal Generator Output Circuit

Vector signal generator can generate custom-build or standard communicationstimulus signal with a variety of filter types, burst waveform and digital modulationformats. It can generate common analog modulation (AM, FM, PM) signal, and havegood precision and linearity, it is an essential testing instrument for developing andtesting radio digital communication system receiving equipment. With the developmentof vector signal generator module as the background, the thesis aims to design andrealize the RF output circuit of signal source,which main characteristics are highmodulating precision,wide range of power change,wide bandwidth and high purityfrequency spectrum of output signal. The output module performance will have a directinfluence on the performance of signal source.The output circuit has realized the power control and pulse modulation function ofsignal source, the power control circuit is the main content discussed by the thesis. Thispaper firstly determined the control scheme of the output signal power, thecorresponding PIN attenuation circuit and its driving circuit is designed according to therequirements, the PIN attenuation is equivalent to a variable resistance changes linearlywith the control current at microwave frequencies. Then designed the RF channel poweramplifying circuit, pulse modulation unit, the mixer circuit and drive circuit, whichmixing the250KHz~250MHz signal. The RF power detection circuit was designed atthe RF output, the demodulation voltage was transformed by dual slope logarithmicamplifier circuit, calibrated through the DAC preset voltage control circuit, converted toa linear control voltage to demodulate the part of the signal power coupled from RFoutput. The integral holding circuit was designed to keep power when the power is notdetected.This paper also introduced the other key technologies of output circuit, includingRF PCB board design, the EMC design and power supply circuit. PCB board design hasintroduced laminated selection, width design and impedance matching and other relatedcontents of RF PCB board; electronic compatibility design introduced the method ofusing electromagnetic compatibility in terms of the layout, grounding, decoupling circuit and so on; power supply circuit provided DC power supply for all analog circuitand digital circuit of the entire output circuit.This paper has realized the hardware circuit after large-scale ADS simulation, theoutput circuit is work well through debugging, indicators are to meet the basicrequirements, The frequency range is from250kHz to4GHz, output power is in therange of20dB, the output resolution is0.1dB, the output power flatness below2G isless than3dB, with high spectral purity, all of which have verified the feasibility of theoutput circuit scheme.