Frequency Synthesizer. Aviation Communications Equipment Are Developed

With the development of technologies, frequency synthesizer becomes a core part within avionics communication equipment. The recent high speed advancement of electronic technology has proposed higher requirement on frequency synthesizer. The frequency synthesis technology providing lower phase noise, higher clutter suppression capability, shorter frequency conversion time, and lower power consumption will become the future development trend.Although simplex frequency synthesis methods can be ideal for some parameters, but can not meet all technical specification requirements. Because different advantages and shortages are provided by various frequency synthesis methods, several methods can be combined in application to take advantages of them; this is so called mixed frequency synthesis technology. DDS (Direct Digital Synthesis) + PLL (Phase Locked Loop) is a mixed frequency synthesis method applied most widely.In this paper, the PLL basic principle is introduced firstly and its linear performance is analyzed. Then DDS basic principle is introduced and its advantages and shortages are analyzed. With the features of this subject are considered and the scheme is demonstrated, the DDS method has finally been used to generate RF signals in 70MHz～100MHz band, and the DDS+PLL method has been used to generate RF signals in 1005MHz～1125MHz band. In this dissertation, direct digital synthesis technology has been used in the phase-locked-loop frequency synthesizer, which can make full use of the characteristics of direct digital synthesis technology such as flexible output wave shape and continuous phase, high frequency stability, high resolution of output frequency, high frequency conversion rate, low output phase noise, low power consumption, small volume,and the characteristics of phase-locked loop such as large band width, high operating frequency, good quality of spectrum together. So we effectively got output spectrum with low phase noise and good spurs under wide band condition.The test results shows that designed frequency synthesizer can meet system design requirements. Some advices are proposed at the end of the paper to improve system performance.