Patent ID: 8022789

Claim:
A tuning arrangement for a resonant circuit, the tuning arrangement having an output reactance dependent upon a plurality of input applied signals, one of which is an input tuning signal, the tuning arrangement comprising: an array of tuning circuits connected in a network whose output reactance is used to control a resonance frequency of the resonant circuit, each tuning circuit having a control input and having a reactance which varies in dependence upon a value of a control signal applied to the control input; means for generating a plurality of control signals for application to the control inputs of the tuning circuits; and the control signal for each tuning circuit varying substantially linearly with the input tuning signal throughout a predetermined range specific to that control signal so that a frequency response of the resonant circuit to the input tuning signal is substantially linear throughout a desired range of the input tuning signal, wherein the means for generating the plurality of control signals comprises a resistive network in the form of a ladder, wherein the plurality of input applied signals are applied to the top and bottom of the ladder, and the plurality of control signals are derived from potentials on one side of the ladder, resistances in the ladder being arranged such that proportions of the individual input applied signals that are derived at control ports of the ladder result in the creation of adjustments to a tuning response that are polynomial functions of an input tuning signal level, these polynomial functions being quasi-orthogonal functions of a third order or less for the plurality of input applied signals that are independent of the input tuning signal, and application of the plurality 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 one order higher than said third order or less, whereby the tuning response to the input tuning signal can be adjusted and set to be substantially linear.