Design Of Broadband Digital Tuning Frequency Agile Voltage Controlled Oscillator

With the development of digital equipment and information technology, the requirementof digitization on broadband microwave oscillator is proposed. Frequency agile or spreadspectrum and hopping is widely used in Digital tuned oscillator to improve theanti-interference ability of equipment. Thus, the microwave oscillator requires the capabilitiesof frequency hopping or frequency agile. As a new microwave solid state signal source,Digital Tuned Oscillator (referred DTO) has advantages of broadband, compensated tuninglinearity, less fluctuated power, good temperature stability and so on. For achieving wide band,frequency agile and digital tuning, this thesis deeply studies the technology of broadbanddigital tuned and frequency agile oscillator.This thesis starts with introducing the research status of digital tuning oscillator, then thebasic theory of digital tuned oscillator is given, and it is proposed a new design method aboutbroadband digital tuned and frequency agile oscillator. In this program, the frequency code isdelivered to the FPGA for addressing ROM as address code and reading the binary digitalcode for correcting the voltage, which is stored in the ROM. Then the RF and microwavesignals are transformed from the analog voltage by the VCO, which is changed from thebinary digital code by DAC. The broadband microwave signal is achieved with dividing ormultiplying the RF and microwave signals by the microwave spread spectrum module.According to the requirements of design and performance of high-speed and high-precision,VCO selects a type of HMC587LC4B for its broadband performance. DAC selects a type ofAD7541AJP, producing a negative precision analog voltage with high-speed operationalamplifier together and achieving a positive tuning voltage through an inverting amplifier.Based on the requirement of the miniaturization design, VCO tuned voltage nonlinearand temperature compensation and so on. Firstly, this paper analyzes the choice ofcomponents and the layout of PCB and shows the solution of linearization control circuit.Secondly, VCO produces the same frequency with different tuning voltages at differenttemperature. In order to improve the frequency accuracy of DTO, it shows a solution of temperature compensation. Lastly, this paper analyzes the factors affecting the frequency agileability of digital tuned oscillator and looks for a good method of reducing frequency agiletime, which is to change the value of compensated capacitor to reduce operational amplifierbuilding time. In this research, the signals with a frequency range of2GHz~18GHz isachieved from Digital Tuned Oscillator with the frequency agile time less than1μs, thefrequency accuracy less than±3MHz and the phase noise lower than-75dBc/Hz@100kHz,which meets the desired design goals.