Influence of Instrumental Errors on the Measurement Error of Signal Parameters for the Case of Quadrature Demodulation Application

The quadrature demodulation method is a type of discrete Fourier transform that uses low-pass filtering instead of averaging. This method has great potential for ensuring high accuracy in measuring both the amplitude and phase of a signal, as well as its frequency. The method's high metrological accuracy is due to its ability to reduce the methodological component of measurement errors. In addition, there are instrumental components that can contribute to measurement errors, such as additive, multiplicative, linear and quantization errors. These errors can occur in analog and digital components of the measuring channel. The paper examines the impact of these instrumental components on the observation uncertainty errors in the amplitude, phase and frequency. Mathematical ratios expressions are derived that allow to evaluate the overall uncertainty of the measured parameters of signal based on all specified components of instrumental error. When estimating the linearity error, different approaches of its mathematical description its form are considered: third-order polynomials, pseudorandom functions and harmonic functions. The influence of signal postprocessing - the measurement result for the parameter under consideration - on the final measurement error is also assessed. The accuracy of the derived analytical ratios was validated by comparing the results of analytical calculations and assessment by Matlab/Simulink simulation.