Finding the Initial Estimate for the Diode Bias Point in Multiport Receivers

In this brief, a novel methodology for estimating the initial diode bias voltage in multiport receivers was developed. We tested the methodology for four different Schottky diodes from different vendors (Win Corp, HP, Hitachi, and Siemens), but the process can be applied to any diode. The analysis shows that setting the initial value for the optimizer where the diode's output dc voltage to input power sensitivity is highest yields the fastest convergence time for the error vector magnitude (EVM) optimizer algorithm. This point is located at the inflection point of the first derivative of the I-V curve fitting polynomial which was obtained in MATLAB and assures that the optimizer will not be trapped into local minima. To verify the results of this research, we used a Simulink model that emulates the radio frequency and digital base band parts of a six-port receiver. It was found that, by reducing the voltage difference between the estimated initial value and the optimum point, the optimizer needed less steps to reach the optimum value of the bias voltage. This work also provides the behavior of the variation of the initial estimates of the diode voltage with the polynomial degree. Hence, the necessary degree for the fitting polynomial can be determined based on the initial point variation analysis.