Fractional-N frequency synthesizer

Abstract

The invention provides a fractional-N frequency synthesizer, which can effectively inhibit integer-N boundary spurs. A reference signal frequency division output unit, a VCO (voltage controlled oscillator) frequency division output unit, a Delta-Sigma modulator and a phase discriminator are integrated on an integrated circuit, so that the interference of external noises can be effectively reduced. An LVDS (low voltage differential signaling) wire input into the integrated circuit from a reference clock unit and an LVDS wire output from the integrated circuit by the phase discriminator form a 90-degree layout, and an LVDS wire output from the integrated circuit by the phase discriminator and an LVDS wire input into the integrated circuit from a VCO form a 90-degree layout, so that the probability of intermodulation between higher harmonics of a reference clock and the output frequency of the VCO can be maximally reduced, and the inhibition degree of the integer-N boundary spurs furthercan be decreased. Moreover, a reference clock signal and an output signal of the VCO are transmitted by adopting the LVDS wires, so that the amplitude of the transmitted signals is low, and even though the two signals are intermodulated, the power of intermodulation interference is low and almost can be neglected.

Description

technical field [0001] The invention relates to frequency synthesis technology, in particular to fractional frequency synthesis technology. Background technique [0002] In both wireless communication systems and electronic measurement and test systems, high-speed oscillating radio frequency signals are required to achieve modulation and demodulation. With the increasingly complex communication system and more and more wireless electromagnetic spectrum interference, the system puts forward higher requirements on the indicators of signal sources. The stability of the signal source, phase noise and frequency conversion time will directly affect the performance of the system. For example, in a radar system, the deterioration of the phase noise of the frequency source will directly lead to the decrease of the resolution of the target. At the same time, the uninterrupted fast scanning of the radar requires the frequency source to provide a high switching speed. How to provide ...

AI Technical Summary

Problems solved by technology

[0005] Due to the limitation of integrated circuit capacity, the number of digits of the delta-sigma modulator in the existing commercial fractional frequency division chips cannot be very high. Theoretically, the higher the number of digits, the higher the frequency accuracy

Images