On the zero- and first-order interpolation in synthesized sine waves for testing purposes

The authors report on the quality requirements of synthesized sine waves reconstructed through a zero or first-order hold intended for testing purposes, in particular, when a switching demodulator is used. In this case, there is a need for great spectral purity only near the carrier rather than throughout the band. It is shown that the best method for obtaining great spectral purity near the synthesized frequency is by use of a zero-order hold instead of a first-order hold. Results show that even though a first-order hold implies a decrease of the total harmonic amplitude distortion (THD), the measured spurious harmonics are kept lower than or equal to those for a first-order hold when a zero-order hold is used in the 15 closest components. It is concluded that in testing applications a zero-order hold, in spite of its greater THD, yields better results than a first-order hold