Electrically tunable inductor and method

Abstract

A radio receiver having a tunable RF stage with an electrically tunable inductor is disclosed. The tunable inductor consists of a magnetic device with a core whose degree of magnetic saturation is controlled by various control currents. A phase lock loop with a programmable frequency divider responds to inputs from a tuning control means and provides a local oscillator signal to a mixer in the radio receiver while also providing a control current to the magnetic device, defined herein as Current Controlled Inductor (C.C.I.), which is directly related to the frequency of the local oscillator signal supplied to the mixer. Each time the radio receiver is tuned to a different input frequency by changing the frequency of the local oscillator signal, a predetermined reference current is applied to the C.C.I. before a new control current corresponding to the new local oscillator frequency is applied. This results in always tuning the C.C.I. in a single direction and therefore accurately setting the C.C.I. to desired values of inductance despite any hysteresis characteristic of the C.C.I. During the time that the C.C.I. is being set by the reference current, a muting signal is created by a monostable multivibrator which silences the speaker of the receiver via an audio gate. In this manner the receiver effectively ignores the time that the C.C.I. is being set by the reference current.