Frequency Stability Improvement in Direct Digital Frequency Synthesis

Abstract

The paper describes a digital frequency synthesizer that incorporates a novel method of the clock signal frequency versus temperature dependency compensation. The clock signal is derived directly from a dual mode crystal oscillator (DMXO). With introducing the method, synthesized signal frequency versus temperature instability below a0.15ppm can be obtained over a wide temperature range (between 45°C and +85°C). Since a temperature information is obtained directly from a crystal itself rather than from an external sensor, temperature offset and lag effects are eliminated.