A direct digital synthesizer with a tunable error feedback structure
Jouko Vankka · IEEE Transactions on Communications · 1997
A basic premise for a direct digital synthesizer (DDS) with error feedback (EF) is that the output frequency being generated is low with respect to the clock frequency used. This is necessary because the transfer function of the EF has zero(s) at DC. In the proposed architecture the clock frequency need only be much greater than the bandwidth of the output signal, whereas the output frequency could be any frequency up to somewhat below the Nyquist frequency. In this novel method, the coefficients of the EF filter are tuned according to the output frequency.