10 Conclusion

Using Davies’ approach is a straightforward method for generating sinusoids having consistent amplitude, frequency, and harmonic distortion. The approach can be tailored as needed for frequencies up through 10s of MHz using simple and inexpensive MSI shift register logic such as the HCS series from Texas Instruments. Starting first with a stepped sinusoid dramatically reduces the harmonic filtering required to obtain the final output, and the shift register can be lengthened as needed to further relax filtering requirements. Starting with a lookup table and applying a simple algorithm to choose from standard EIA series optimizes the THD performance without requiring custom value resistors. The output frequency can be changed virtually instantaneously, and tunable harmonic filters can be constructed from switched-capacitor networks for outputs having a wide spectrum of output. Multiphase outputs are also possible. These circuits are easily simulated in SPICE, though harmonic distortion predictions can be carefully scrutinized since only harmonics up through the Nyquist frequency can be included, and modeling limitations can mask the true non-linearities of the devices used.