Phase amplitude converter with conditional shift operation

This paper proposes a new type of approximation method for sine wave and the proposed method is applied to phase amplitude converter (PAC) used in direct digital frequency synthesizer (DDFS). The approximation is carried out by conditional shift operation (CSO) that reshapes the sawtooth signal from phase accumulator. As the signal purity of the CSO-PAC is not good enough, error correction is employed to improve the signal purity. VHDL simulations along with the circuit size and speed evaluations, are conducted to verify the feasibility of the proposed method. The comparison among other types of PACs shows that the advantage of the proposed PAC is its circuit size. Especially the CSO-PAC without the error correction, is quite small and it can operate at a very high frequency clock. Thus the CSO-PAC may be a good choice for those applications that do not require high purity signal.