Tuning circuit for a high frequency heterodyne receiver with tuning controlled by direct voltage

Claim 1

In a circuit for a high frequency heterodyne receiver, including a controllable reactance element connected to receive a tuning voltage to effect tuning, an electronic counter for digital determination of the reception frequency by periodic counting of the oscillations of at least one heterodyne oscillator of the receiver, a selection memory, a comparator connected for comparing the result of counting by the counter with the content of the selection memory, an evaluation circuit connected for evaluating the result of the comparison, and an integrating circuit including a capacitor connected to be controlled by the evaluation circuit for producing the tuning voltage, the improvement wherein said circuit further comprises means connected to supply a charging current to said capacitor, said means including a source of an auxiliary voltage, a plurality of circuit units connected in parallel with one another between said voltage source and said integrating circuit, each said circuit unit being composed of a series arrangement of a resistor and an electronic switch connected to have its switching state controlled by a respective component of the comparison result produced by said comparator, whereby the charging current to said capacitor is a function of the value of the auxiliary voltage and the switching states of said electronic switches, and regulating means connected for causing the value of said auxiliary voltage to be a function of the value of said tuning voltage.