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

The authors deal with the quality requirements of synthesized sine waves reconstructed through a zero- or first-order hold for testing purposes, particularly when a switching demodulator is used. In this case, the interest is to have great spectral purity near the carrier rather than in all of the band. It is shown that the best method to obtain great spectral purity in the frequency band close to the synthesized frequency is by using zero-order hold instead of a first-order hold. Results show that even though a first-order hold implies a decrease of total harmonic amplitude distortion (THD), the measured spurious harmonics are kept lower or equal when using a zero-order hold 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