Automatic frequency control apparatus

Claim 2

Frequency discriminating apparatus comprising: a differential amplifier having a pair of input terminals and a pair of output terminals; first and second detector networks, each having an input terminal and an output terminal coupled to one of said pair of differential amplifier input terminals; means for supplying input signal waves having a frequency within a band including a predetermined reference frequency; a phase shift circuit tuned to said reference frequency and responsive to said signal waves for providing signals to the input terminals of said first and second detector networks which are shifted in phase with respect to said signal waves by an amount proportional to the frequency deviation of said waves from said reference frequency; and means coupled to said detector networks for inhibiting the operation thereof until the amplitude of said signals exceeds a predetermined threshold value; the apparatus being so constructed and arranged that direct voltages proportional to said frequency deviation are developed at said pair of differential amplifier output terminals.

Claim 3

Frequency discriminating apparatus as defined in claim 1 wherein each of said detector networks includes a first transistor having base and emitter electrodes respectively connected to the input and output terminals of said detector and a filter capacitor coupled between said detector output terminal and a point of reference potential, and wherein said inhibiting means includes means for biasing said detector transistors to a nonconducting condition for signals having an amplitude less than said threshold value.

Claim 4

Frequency discriminating apparatus as defined in claim 2 wherein said inhibiting means includes a second transistor having its collector and emitter electrodes respectively coupled to corresponding electrodes of said detector network transistor and having its base electrode coupled to a point of direct bias voltage different form that coupled to the base electrode of said detector transistor, to render said detector transIstor nonconducting until the amplitude of said signals exceed said threshold value.

Claim 5

Frequency discriminating apparatus as defined in claim 3 wherein said differential amplifier includes a pair of transistors, each having base and collector electrodes respectively connected to the input and output terminals of said differential amplifier, and a further transistor coupled to each of their emitter electrodes for supplying a constant current thereto which divides in said amplifier transistors in accordance with the respective conductivities thereof.

Claim 6

Frequency discriminating apparatus as defined in claim 4 wherein said input signal supply means includes an amplifier stage and wherein there is further included: means coupled to said further transistor of said differential amplifier for deriving a direct voltage therefrom indicative of the amplitude of said supplied signals, and for coupling said direct voltage to said amplifier stage to vary the bias thereof so as to stabilize the amplitude of said signals provided said detector transistors once said threshold value is exceeded.

Claim 7

In combination: first, second, third and fourth terminals; first, second, third, fourth, fifth and sixth transistors; a first resistor coupling the collector electrode of said first transistor to said first terminal; a second resistor coupling the collector electrode of said second transistor to said first terminal; a first capacitor coupling the base electrode of said first transistor to said second terminal; a second capacitor coupling the base electrode of said second transistor to said second terminal; means coupling the emitter electrodes of said first and second transistor to said second terminal; direct current connections between the collector electrodes of said third, fourth, fifth and sixth transistors and said first terminal; direct current connections between the emitter electrodes of said third and fourth transistors and the base electrode of said first transistor; direct current connections between the emitter electrodes of said fifth and sixth transistors and the base electrode of said second transistor; a first source of bias potential; means for coupling said first source to the base electrodes of said third and said sixth transistors; a second source of bias potential of value different from that provided by said first source; means for coupling said second source to the base electrodes of said fourth and fifth transistors; direct current connections from the collector electrodes of said first and second transistors to said third and fourth terminals, respectively; means for supplying input signal waves having frequencies within a band including a predetermined reference frequency; and a phase shift circuit tuned to said reference frequency and responsive to said signal waves for providing signals to the base electrodes of said third and sixth transistors which are shifted in phase with respect to said signal waves by an amount proportional to the frequency deviation of said waves from said reference frequency; the apparatus being so constructed and arranged that direct signal voltages proportional to said frequency deviation are developed at said third and fourth terminals when the amplitude of said signals provided said third and sixth transistors exceeds the difference in voltage between said first and second sources of bias potential.

Claim 8

In combination: first, second, third and fourth terminals; first, second, third, fourth, fifth and sixth transistors; a first resistor coupling the collector electrode of said first transistor to said first terminal; a second resistor coupling the collector electrode of said second transistor to said first terminal; a first capacitor coupling the base electrode of said first transistor to said second terminal; a second capacitor coupling the base electrode of said second transistor to said second terminal; means coupling the emitter electrodes of said first and second transistor to said second terminal; direct current connections between the collector electrodes of said third, fourth, fifth and sixth transistors and said first terminal; direct current connections between the emitter electrodes of said third and fourth transistors and the base electrode of said first transistor; direct current connections between the emitter electrodes of said fifth and sixth transistors and the base electrode of said second transistor; a first source of bias potential; means for coupling said first source to the base electrodes of said third and said sixth transistors; a second source of bias potential of value different from that provided by said first source; means for coupling said second source to the base electrodes of said fourth and fifth transistors; direct current connections from the collector electrodes of said first and second transistors to said third and fourth terminals, respectively; means for supplying input signal waves having frequencies within a band including a predetermined reference frequency; and a phase shift circuit tuned to said reference frequency and responsive to said signal waves for providing signals to the base electrodes of said third and sixth transistors which are shifted in phase with respect to said signal waves by an amount proportional to the frequency deviation of said waves from said reference frequency; the apparatus being so constructed and arranged that direct signal voltages proportional to said frequency deviation are developed at said third and fourth terminals when the amplitude of said signals provided said third and sixth transistors exceeds the difference in voltage between said first and second sources of bias potential.