Linear frequency discriminator

Claim 2

A linear frequency discriminator comprising: (a) a phase detector having a pair of inputs and an output, signals at the output being an indication of the phase difference between signals applied to the pair of inputs and one of said inputs of said phase detector being adapted to receive a modulated input signal; (b) a tuned circuit including a variable reactance and having an output connected to the other of said pair of inputs of said phase detector, said tuned circuit further having a signal input for receiving said modulated input signal, and a control input for receiving a control signal derived from the signals at said output of said phase detector to adjust said variable reactance and retune the tuned circuit to track the frequency of said modulated input signal; (c) said variable reactance including a fixed capacitive means and an amplifier means connected so that the reactance of said variable reactance depends on the current gain of said amplifier means, said current gain of said amplifier means varying as a function of said control signal, said tuned circuit having a nonlinear relationship between the resonant frequency thereof and the value of said variable reactance, and said amplifier means including a nonlinear element for counteracting said nonlinearity in said tuned circuit to provide a signal at said output of said phase detector which varies linearly with changes of phase in said modulated input signal; and (d) means for connecting signals at said output of said phase detector to said control input of said tuned circuit and for providing the output signal of the linear frequency discriminator.

Claim 3

A linear frequency discriminator as claimed in claim 1 wherein the phase detector is a multiplier.

Claim 4

A linear frequency discriminator as claimed in claim 1 wherein said tuned circuit provides a quiescent phase difference between said pair of inputs of the phase detector of approximately 90°.

Claim 5

A linear frequency discriminator as claimed in claim 1 wherein said amplifier means includes a differential amplifier with common emitters and a variable current source in the common emitter circuit, said amplifier means further including circuitry connected to the variable current source for controlling the variable current source in accordance with said control signal which is applied thereto.

Claim 6

A linear frequency discriminator as claimed in claim 4 wherein the differential amplifier has a base input connected to said variable current source and the circuitry controls current applied to said base input and the common emitter circuit in accordance with said control signal, said circuitry operating nonlinearly by providing a current in the amplifier which includes a square term.

Claim 7

A linear frequency discriminator as claimed in claim 1 wherein said means for connecting signals includes a filter and an amplifier.

Claim 8

A linear frequency discriminator as claimed in claim 1 including a variable capacitance in the tuned circuit, a comparator having a pair of inputs with a reference signal representative of a predetermined frequency applied to one of the inputs and the other input connected to the output of the phase detector, said comparator having an output connected to said variable capacitance for adjusting said variable capacitance to tune the tuned circuit until the signal at the output of the phase detector compares to the reference signal.

Claim 9

A linear frequency discriminator as claimed in claim 7 including in addition means for applying a periodic reference signal having a frequency equal to the predetermined frequency to said one of said pair of inputs of said phase detector for adjusting the discriminator to the reference signal.

Claim 10

A linear frequency discriminator as claimed in claim 8 wherein said means for applying a signal include circuitry providing a television synchronizing signal with the signal having the predetermined frequency periodically impressed thereon.

Claim 11

A frequency discriminator comprising: (a) a phase detector having a pair of inputs and an output and including a tuned circuit for providing a phase difference between signals applied to the pair of inputs; (b) means responsive to said output of said phase detector for providing the output signal of the frequency discriminator; (c) a variable capacitance having an input for receiving a control signal to adjust the capacitance thereof and connected into the tuned circuit of said phase detector; (d) a comparator having a pair of inputs with a reference signal representative of a predetermined frequency applied to one of the inputs and the other input coupled to the output of the phase detector, said comparator having an output connected to the input of said variable capacitance for adjusting said variable capacitance to tune the tuned circuit until the signal at the output of the phase detector compares to the reference signal; and (e) means for applying a signal having a predetermined frequency to said one of said pair of inputs of said phase detector for tuning the tuned circuit to a predetermined reference value.

Claim 12

A frequency discriminator comprising: (a) a phase detector having a pair of inputs and an output and including a tuned circuit for providing a phase difference between signals applied to the pair of inputs; (b) means responsive to said output of said phase detector for providing the output signal of the frequency discriminator; (c) a variable capacitance having an input for receiving a control signal to adjust the capacitance thereof and connected into the tuned circuit of said phase detector; (d) a comparator having a pair of inputs with a reference signal representative of a predetermined frequency applied to one of the inputs and the other input coupled to the output of the phase detector, said comparator having an output connected to the input of said variable capacitance for adjusting said variable capacitance to tune the tuned circuit until the signal at the output of the phase detector compares to the reference signal; and (e) means for applying a signal having a predetermined frequency to said one of said pair of inputs of said phase detector for tuning the tuned circuit to a predetermined reference value.

Claim 13

A linear frequency discriminator as claimed in claim 10 wherein the means for applying the signal includes circuitry for applying the signal periodically.

Claim 14

A linear frequency discriminator adapted to receive a composite signal having periodic information signals with standard frequency signals periodically interposed therebetween comprising: (a) a phase detector having first and second inputs and an output, signals at the output being an indication of the phase difference between signals applied to the first and second inputs; (b) a tuned circuit including a variable reactance and having an output connected to one of the first and second inputs of said phase detector, said tuned circuit further having a signal input adapted to receive the composite signal and connected to the other of the first and second inputs of said phase detector and a control input for receiving a control signal to adjust the variable reactance and retune the tuned circuit to track the frequency of the periodic information signals of the composite signal at the signal input; (c) means for connecting signals at the output of said phase detector to the control input of said tuned circuit and for providing the output signal of the frequency discriminator; (d) a variable capacitance connected into said tuned circuit for controlling the resonance thereof and having an input for receiving a control signal to adjust the capacitance thereof; (e) a comparator having a pair of inputs with a reference signal representative of a predetermined frequency applied to one of the inputs and the other input coupled to the output of said phase detector, said comparator having an output connected to the input of said variable capacitance for adjusting said variable capacitance to tune the tuned circuit until the signal at the output of said phase detector compares to the reference signal; and (f) switching means connected to said comparator for turning off said comparator during reception of the periodic information signals and turning on said comparator during reception of the standard frequency signals.

Claim 15

A linear frequency discriminator adapted to receive a composite signal having periodic information signals with standard frequency signals periodically interposed therebetween comprising: (a) a phase detector having first and second inputs and an output, signals at the output being an indication of the phase difference between signals applied to the first and second inputs; (b) a tuned circuit including a variable reactance and having an output connected to one of the first and second inputs of said phase detector, said tuned circuit further having a signal input adapted to receive the composite signal and connected to the other of the first and second inputs of said phase detector and a control input for receiving a control signal to adjust the variable reactance and retune the tuned circuit to track the frequency of the periodic information signals of the composite signal at the signal input; (c) means for connecting signals at the output of said phase detector to the control input of said tuned circuit and for providing the output signal of the frequency discriminator; (d) a variable capacitance connected into said tuned circuit for controlling the resonance thereof and having an input for receiving a control signal to adjust the capacitance thereof; (e) a comparator having a pair of inputs with a reference signal representative of a predetermined frequency applied to one of the inputs and the other input coupled to the output of said phase detector, said comparator having an output connected to the input of said variable capacitance for adjusting said variable capacitance to tune the tuned circuit until the signal at the output of said phase detector compares to the reference signal; and (f) switching means connected to said comparator for turning off said comparator during reception of the periodic information signals and turning on said comparator during reception of the standard frequency signals.