Investigation of the Frequency Response Characteristic of the Software Phase-locked Loop

The goal of this paper is an experimental measurement of the frequency response of the software phase-locked loop (PLL) transfer function using frequency modulated signals.

The article describes the block diagram of the PLL and its main components. The paper also presents formulas for the PLL transfer function, one of which is expressed through the parameters of the PLL components, and another is presented in normalized form. The measurement method of the frequency response of the PLL transfer function is explained and expression for its calculation is displayed. A block diagram of the PLL hardware part is presented in the paper as well. Moreover, the article depicts an algorithm of the PLL software part. Further in the article, the diagrams of experimentally obtained frequency response are built for various PLL parameters. These plots also contain theoretically calculated PLL frequency response.

Comparison of theoretical and experimental data gives an opportunity to make the conclusion that mentioned measurement method provides a high-quality assessment of the PLL frequency response with sufficient accuracy.