The Research Of The Ultra-wideband And Small-step Frequency Synthesizer

As the core of the modern electronic equipment, frequency synthesizer plays a veryimportant role in the military and civil. Ultra-wideband, small-step, low-phase-noiseand fast-hopping frequency synthesizer becomes the development trend of modernfrequency source. Therefore, the research of wideband and small-step frequencysynthesizer has a very important value.According to the index to be achieved, It puts forward a reasonable scheme, takingadvantage of the characteristics of the DDS to provide small-step frequency. Thescheme is divided into four modules to implemente the wideband and small-stepfrequency synthesizer. The thesis verifies the scheme and calculates the main indexincluding the frequency range, the frequency resolution, the output power, the powercontrol range, the phase noise and the spur. After calculation, the scheme can meet therequirements.The scheme is divided into two parts: the hardware and the software. The hardware isdivided into four modules: the power module, the reference module, the main-loopmodule and the frequency-extension module. The power module provides a stable andreliable operating voltage for the system. The reference module provides a variable andsmall-step reference signal with DDS and a2GHz local oscillator signal with a PLL.The main-loop module, a phase locked loop, provides2-4GHz signal. The frequency-extension module controls the output power using an open-loop ALC with a attenuatorand a variable gain amplifier, and suppresses signal harmonics and spurious. Thesoftware controls every module, communicates between modules by SPI andcommunicates with the computer by RS232.After troubleshooting and testing, the system’s output frequency ranges from10MHzto4GHz with100Hz for frequency stepping. Its output power ranges from-30dBm to+10dBm with1dB for power stepping. Phase noise is-80dBc/Hz@10kHz and-100dBc/Hz@100kHz when the output frequency is4GHz. Non-harmonic spur is betterthan-70dBc.