A Method for Reducing the Static Error of a Quadrature Demodulator by the Application of Additional Measuring Channel

Quadrature demodulation, in addition to its main purpose in information transmission systems, can be used in measurement technique as an alternative to the discrete Fourier transform. Similar to the discrete Fourier transform, the application of quadrature demodulator allows to obtain the values of the amplitude, phase spectrum and frequency of the signal. The implementation of a quadrature demodulator is associated with a number of difficulties, primarily of a practical nature. The digital filter, especially its recursive versions, can cause the great number of problems. Existing solutions aimed at increasing accuracy lead to increased measurement time, which can become a serious problem. This paper proposes a new approach to designing a quadrature demodulator that allows partial compensation of the error signal at the demodulator output. This leads to a significant reduction in the requirements for the demodulator output filter and a reduction in the overall measurement time. As a result, due to the reduction in measurement time, additional techniques can be successfully applied aimed at reducing the measurement error of the considerate parameters. The main disadvantage of the proposed approach is lower interference sensitivity from the input signal harmonics and input noise. In paper the main sources of error in the proposed approach are examines and suggests ways to reduce them. To test the effectiveness of the approach, a simulation model of the considerate modified demodulator was proposed in Simulink package and the measurement error was assessed for the case of sinusoidal and polyharmonic signals. A comparative analysis of the proposed modification and the standard demodulator was performed in terms of the achieved accuracy and complexity of the final implementation.