Simulation of the image rejection phase method

Abstract

The paper considers the algorithmic possibility of the image rejection method. The main resulting characteristics of circuits implementing the above method are presented. The simulation model allows estimating the selectivity coefficient as a function of the phase and amplitude imbalance of the circuit branches. Mathematical and circuit simulations were conducted. The results of different modeling methods coincide, and the simulation results verify the possibility of implementing the image rejection method. On the basis of this model it is possible to provide a high level (at least 40 dB) of image rejection by amplitude and phase circuit imbalance compensation. The dependence of the noise level at the output of the image rejection circuit as a function of the circuit elements frequency characteristics is given. The results of this work could be used for further practical implementation of above mentioned method at the stage of selecting elements based on an analysis of their characteristics. The simulation model could be used to select required radioelements and to estimate image rejection level. It is possible to estimate the level of image channel suppression, the noise level and the signal-to-noise ratio at the output of the image rejection circuit by using the above mentioned mathematical models and characteristics of the selected elements for practical implementation of the circuit. The effect of the broadband phase shifters on the noise level is considered with the implementation of the above method as an example. It was shown that ensuring a high level of selectivity in order to minimize the noise level of the image channel is advisable only up to some values (about 25 dB). Further improvement of selectivity, for example, by minimizing the phase and amplitude balances, or mutual compensation of the mixer and phase shifter branch imbalances are necessary, if there are requirements for increasing the signal-to-noise ratio. It is shown that it is possible to ensure selectivity of up to 25 dB and a noise level reduction of 2.5-3 dB if the amplitude imbalance of the circuit is up to 1 dB, and the phase imbalance is up to 5 deg. in the required frequency band.