Tuning using control signals generated by a resistive network ladder using quasi-orthoganal polynomial functions

摘要

Disclosed is a tuning arrangement for a resonant circuit, the tuning arrangement comprising: an array of tuning circuits connected in a network and means for generating a plurality of control signals. The network has an output reactance dependent upon a plurality of input applied signals one of which is an input tuning signal, the output reactance being used to control the resonance frequency of the resonant circuit. Each tuning circuit has a control input and has a reactance which varies in dependence upon the value of the control signals, which are applied to the control input. The control signal for each circuit varies linearly with the input tuning signal through a predetermined range specific to that control signal so that the frequency response of the resonant circuit to the input tuning signal is linear throughout a desired range of the input tuning signal. The means for generating control signals comprises a resistive network in the form of a ladder, with the input applied signals applied to the top and bottom of the ladder, and the control signals are derived from the potentials on one side of the ladder. The resistances in the ladder are arranged such that the proportions of the individual input applied signals that are derived at the control inputs result in the creation of adjustments to the tuning response that are polynomial functions of the input tuning signal level. These functions are quasi-orthogonal functions of the third order or less for input applied signals that are independent of the input tuning signal, and application of input applied signals that are dependent on the input tuning signal to the top and bottom of the ladder results in a modification to the tuning response that has a power dependency that is of the fourth order. The tuning response to the input tuning signal can be adjusted and set to be substantially linear.