The High Purity Of The L-band Frequency Source

Frequency Synthesizer is the heart of all the electronic systems. It determines the performance of the electronic equipments. Along with the development of wireless communication, modern military and national defense, many systems, such as radars, guided weapons, mobile communication, electronic measurement and c countermeasure, need higher and higher performance of synthesizers, which include wide frequency range, low phase noise, high spur suppression, low setting time and high output frequency. Many countries in the world have been playing more and more attention on the research and application of it.The project, named High Purity Frequency Source, comes from an item of new product research accepted by the Research Cantle of Electronic System Engineering of UESTC.The product will be used as the local oscillator of receiver. The frequency source can product L-band signal with 200MHz bandwidth and 21 frequency points. It's output has relatively high purity of spectrum to satisfy the requirements for detecting the minute feature. The basic specifications, such as phase noise, spur suppression and setting time are relatively strict.The PLL scheme is put to use in the High Purity Frequency Source. The specifications of phase noise and spur suppression can be satisfied by using PLL IC with ultra-low nominal phase noise floor and designing PLL circuits carefully. Two-PLL scheme is applied and they work by ping-pang manner to realize the setting time of severalμs. By this scheme, the sample has been reached the specifications needed.At first, the basic theme of PLL, mechanism of phase noise and designing methods of PLL-frequency synthesizers are reviewed in the paper. Subsequently, the comparison of the schemes, computer simulation, circuit design and the realization of hardware are developed. Finally, the testing results of the sample also be given.