10MHZ-6GHZ Frequency Synthesizer Study

Frequency synthesizer is one of most important part of modern electronic device, it has been widely used in communication, navigation and Global Positioning System. As the technology develop, wide band, low phase noise, low spur, high frequency resolution and fast tuning speed become the key goal which the frequency synthesizer chase.According to the device index, my paper design the power, reference loop, main loop and frequency extend part of the 10MHz-6GHz wide-band frequency synthesizer. And then finish the circuit adjustment work. The frequency synthesizer based on Phase-Lock loop(PLL) and Direct Digital Synthesis(DDS) technology and realize high resolution and wide band.The hardware design of the work are: the power of the system, PLL with DDS, frequency extend. Power of the system use a transformer drop down the 220 V AC and then rectifier bridge convert the double-sided current to single-sided current. This single-sided current flow through the filter and regulator becoming DC which is suitable for each part of the system; DDS is programmable, insert the DDS into the feedback loop of the PLL may provide small-step of frequency tuning; Frequency extend part use the Divider and Mixer to extend the frequency range. The software design of the work are: program of the ARM and MCU. ARM Development Board named TQ2440 is the manufacture by Tian Qian company. The ARM run under the Windows Embedded CE operating system, my work is to design a control window. Users can input the desire frequency and power, choose the output mode by the keyboard. What you input on the keyboard can display on the LCD on the ARM. Then the ARM sent what you input to each part of the system by SPI Bus. MCUs on the Main Loop and Frequency Extend receive the control instruction by SPI and adjust the working state of each part.According to the physical test data, the output frequency of the system cover 10MHz-6GHz, frequency resolution is 100 Hz, phase noise at 5GHz is-91 d Bc/Hz@10k Hz and-109 d Bc/Hz@100k Hz; none-harmonic spurious less than-45 d Bc. The performance meet the design request.