Recently, there are increasing interests in impedance sensors for various applications. Direct digital synthesis (DDS) circuits are commonly used in such sensor circuits for generating stimulus signals, due to the advantages of accurate frequency control, drift-free performance, etc. Previously reported DDS circuits for sensor applications typically maintain superb frequency accuracy within relatively small frequency ranges. This paper investigates techniques to improve frequency accuracy over wide frequency ranges. In addition, it presents an analytical framework to estimate the signal to noise ratio (SNR) of the generated signal and derives guidelines for optimizing DDS circuit configurations. Both simulation and hardware measurement results are presented to validate the derived SNR estimation equation as well as the developed frequency accuracy enhancement techniques
Leitner, Stefan, Wang, Haibo and Tragoudas, Spyros. "Design Techniques for Direct Digital Synthesis Circuits with Improved Frequency Accuracy over Wide Frequency Ranges." Journal of Circuits, Systems and Computers 26, No. 2 (Feb 2017). doi:10.1142/S0218126617500359.