The design of wide BW frequency synthesizer based on the DDS&PLL hybrid method

Frequency synthesizer is an important component in the modem electronic systems. This paper studied a kind of frequency synthesizer in the UAV system and put forward an improvement method for DDS (Direct Digital Synthesis) & PLL (Phase Locked Loop) hybrid frequency synthesizer. Be further to raise PLL performance in fast locking and noise immunity ability in the improvement method, a PLL with Analog Adaptive Bandwidth Control (AABC) has been designed in this paper. The new-type AABC has been presented based on conventional Charge pump PLL circuit. The PLL with AABC block can control the loop bandwidth according to the locking status and the amount of inputs´ phase error adaptively; and consequently low-noise and fast-lock performance are achieved. End, the designed Frequency synthesizer satisfies an 800 MHz to 1.8 GHz output range and a 0.4 ms maximum conversion time. Working at 900 MHz, the phase noises are-93 dBc/Hz at 200 kHz offset, and the whole circuit draws 8.7 mA current from 3.0 V supply.