Application of Quadrature Demodulation to Measure the Parameters of Polyharmonic Signals

One of the alternatives to the discrete Fourier transform for complex spectrum measurement problems is the quadrature demodulation method. The main advantage of this approach is the high accuracy of measuring both the parameters of the complex spectrum and the frequency. The disadvantages include a significant increase in the complexity of implementation associated with the use of a digital filtering device. Like the discrete Fourier transform, the quadrature demodulation method allows you to obtain amplitude, phase values and frequency for both sinusoidal and polyharmonic input signals. In this article, the case of a polyharmonic input signal is considered. Analytical dependences have been obtained to estimate the measurement error of the amplitude value, frequency and initial phase for a signal of this type. The requirements for the output filters of the demodulator are worked out, the relationship between the filter parameters and the measurement error of the considered signal parameters is shown. The question of the influence of the spectral composition of the signal and the final measurement error is investigated. The complexity of the implementation of such an approach is estimated for the case of measuring the parameters of polyharmonic signals. Schematic and algorithmic methods for reducing the measurement error of these parameters are proposed. The results of the study were verified using simulation mathematical modeling in the Matlab software package.