SAW Discriminators for Low Phase Noise Frequency Synthesizers

Abstract

Delay line discriminators used for phase noise compensation of VCO's have traditionally relied on coaxial or waveguide delay lines. But size constraints, especially at UHF frequencies, limit the range of achievable delays to less than 100 ns, resulting in relatively low sensitivities and correspondingly low phase noise suppression. The introduction of SAW technology readily provides delays in the psec range, and makes possible highly sensitive discriminators which can be used to greatly reduce VCO phase noise. This paper explains the SAW delay line discriminator and its application to noise suppression in indirect frequency synthesizers. Phase noise measurement of a 700 MHz synthesizer with 200 MHz of stepping bandwidth show good agreement with theory. was achieved at 2 kHz from the carrier by using these techniques. A 30dB improvement in phase noise