Direct digital synthesizer clock frequency versus temperature dependency compensation using two look-up tables

The paper describes a novel approach of static frequency vs. temperature dependency compensation of a direct digital frequency synthesizer clock signal. The compensation significantly reduces the frequency vs. temperature dependency of synthesized signals over a wide range of operating temperatures. The clock signal, which samples the direct digital frequency synthesizer, is excited by a dual-mode crystal oscillator. Since the crystal self-thermometry is used, temperature information is obtained directly from the crystal itself rather than from an external sensor and temperature offset and lag effects are eliminated. The designed compensation module can be implemented effectively within many popular field programmable gate arrays or programmable logic devices available today, e.g. using any Spartan-II family device (Xilinx, Inc.).