Design Of Frequency Synthesizer In HF High Speed For Differential Frequency Hopping Transmitter-receiver

The differential Frequency-Hopping (DFH) technique is a new type of the frequency-hopping (FH) communication technique. It is the feature that the relativity between the frequency-hopping carrier waves is utilized to transmit the information. When the DFH technique is used for the HF communication, it can realize the frequency-hopping operation of the broadband and high velocity on the HF band so that the data transmission velocity of the HF communication, the anti-jamming and anti-multipath fading abilitis can be greatly enhanced. This new type of the HF frequency-hopping system will be one of directions in the HF communication field.The frequency synthesizer is the heart of the DFH system. Its performance and specifications have the important influence on the over-all capability of FH. The theory of FH and DFH technique has been systematically described in this paper. The paper also introduces three patterns of the frequency synthesizing techniques: Direct Frequency Synthesis (DS);Phase Lock Loop Frequency Synthesis (PLL);Direct Digital Frequency Synthesis (DDS).The character of each pattern has been analyzed in details. The operating principle, basic structure and frequency spectrum of DDS are introduced. The main resource of the DDS output spur, phase truncation error, amplitude quantization error and the DAC nonlinear error have been analyzed, And give the solutions to decrese the spur. The combined frequency synthesizer including the method of improving the locking speed of DDS and PLL has also been described so that the designing solution of the frequency synthesizer that is suitable for the HF DFH operation has been brought forward.The designing of the HF DFH frequency synthesizer based on DDS+DSP has been completed. The scheme of DFH HF synthesizer is described. DDS chip AD9951 made by ADI company is selected as the synthesizer. The DSP chip TMS320C6418 made by TI company is selected as the high speed controlling circuit.The main contents include the interface design of DSP and DDS, the scattering rejection design, the low phase noise design and the filter design. The solution has passed through the validation of the special experiment, the sample design and the joining trial. It is indicated after the inspection of the complete set that the frequency synthesizer has satisfied the requirement of the frequency converting time so that it has the good frequency spectrum purity and the requirement of the DFH technical specifications can be achieved.