Rapid tuning circuit for high frequency receivers

Claim 1

In a tuning circuit for a high frequency receiver, which circuit includes a voltage controllable superheterodyne oscillator arranged to receive a control voltage and to produce an oscillation whose frequency is determined by the value of the control voltage and determines the broadcast frequency to which the receiver is tuned, a counter connected to sense the frequency of the oscillations being generated by the oscillator and to produce therefrom a count state in the form of representations of the digits of a first decimal number identifying the broadcast frequency to which the receiver is currently tuned, input means for generating representations of the digits of a second decimal number identifying the broadcast frequency to which it is desired to tune the receiver, and a comparison circuit for comparing the decimal number representations being produced by the counter and the input means in order to vary the control voltage in a direction to cause those two number representations to coincide, the comparison circuit including a comparator capable of comparing the representations of one digit of each of two numbers and having two inputs connected, respectively, to the counter and to the input means, the comparator being arranged to receive, at one of its inputs, each digit representation produced by the counter, starting with the most significant digit, and, at the other of its inputs, simultaneously therewith each digit representation of corresponding significance generated by the input means, the comparator including a first output providing a signal when the digit representations at its inputs are identical, a second output providing a signal when the digit representation at its one input represents a value larger than that of the digit representation at its other input, and a third output providing a signal when the digit representation at its one input represents a value smaller than that of the digit representation at its other input, the improvement comprising: tuning voltage adjustment means connected to said comparator outputs and responsive to the number of sequences of termination of a signal at one of said second and third outputs and subsequent initiation of a signal at the other of said second and third outputs for varying the control voltage at a rate inversely proportional to such number of sequences.