Wide bandwidth crystal frequency discriminator circuit

Claim 2

A discriminator circuit for providing a unidirectional output voltage indicative of the instantaneous frequency deviation of a frequency modulated input signal from a center frequency comprising: input circuit means for receiving said frequency modulated input signal; crystal filter means coupled to said input circuit means and having a predetermined voltage versus frequency characteristic including a portion wherein the voltage varies substantially linearly as a function of frequency, said crystal filter means including a crystal resonator having a series resonant frequency at a frequency higher than the frequencies corresponding to said substantially linear portion of said voltage versus frequency characteristic; detector circuit means coupled to said crystal filter means for rectifying the output voltage from said crystal filter means; and voltage level shifting means coupled between said input circuit means and said detector circuit means for algebraically combining the output voltage from said detector circuit means with a dc voltage such that the algebraic sum of said dc voltage and said output voltage from said detector circuit means is zero when the instantaneous frequency of said input signal is at said center frequency.

Claim 3

A discriminator circuit according to claim 1 wherein said voltage versus frequency characteristic has a maximum voltage value substantially at said series resonant frequency, and said crystal filter means has first and second parallel resonant frequencies respectively less than and greater than said series resonant frequency such that the voltage value of said voltage versus frequency characteristic at said first and second parallel resonant frequencies is less than said maximum voltage value by a predetermined amount.

Claim 4

A discriminator circuit according to claim 2 wherein said first parallel resonant frequency is greater than said center frequency and corresponds to a voltage value along said substantially linear portion of said voltage versus frequency characteristic.

Claim 5

A discriminator circuit according to claim 2 wherein said crystal filter means has a third parallel resonant frequency at a frequency substantially equal to said series resonant frequency.

Claim 6

A frequency discriminator circuit comprising: an input terminal, an output terminal and a reference terminal; a transformer having a primary winding and a secondary winding, said primary winding being coupled between said input terminal and said reference terminal, said secondary winding having one terminal coupled to said reference terminal, a first capacitor coupled across said secondary winding; a second capacitor and an inductor coupled in parallel, said inductor having a tap coupled to said reference terminal, a crystal resonator coupled between another terminal of said secondary winding and one terminal of said inductor, a third capacitor coupled between said another terminal of said secondary winding and another terminal of said inductor; a first diode and a first resistor coupled in series between said one terminal of said inductor and said output terminal, a fourth capacitor coupled between said reference terminal and the junction between said first diode and said first resistor; a fifth capacitor, a second diode, and a second resistor coupled in series between said another terminal of said secondary winding and said output terminal, a third resistor coupled between said reference terminal and the junction between said fifth capacitor and said second diode, and a sixth capacitor coupled between said reference terminal and the junction between said second diode and said third resistor.

Claim 7

A frequency discriminator circuit comprising: an input terminal, an output terminal and a reference terminal; a transformer having a primary winding and a secondary winding, said primary winding being coupled between said input terminal and said reference terminal, said secondary winding having one terminal coupled to said reference terminal, a first capacitor coupled across said secondary winding; a second capacitor and an inductor coupled in parallel, said inductor having a tap coupled to said reference terminal, a crystal resonator coupled between another terminal of said secondary winding and one terminal of said inductor, a third capacitor coupled between said another terminal of said secondary winding and another terminal of said inductor; a first diode and a first resistor coupled in series between said one terminal of said inductor and said output terminal, a fourth capacitor coupled between said reference terminal and the junction between said first diode and said first resistor; a fifth capacitor, a second diode, and a second resistor coupled in series between said another terminal of said secondary winding and said output terminal, a third resistor coupled between said reference terminal and the junction between said fifth capacitor and said second diode, and a sixth capacitor coupled between said reference terminal and the junction between said second diode and said third resistor.

Claim 8

A frequency discriminator circuit comprising: an input terminal, an output terminal and a reference terminal; a transformer having a primary winding and a secondary winding, said primary winding being coupled between said input terminal and said reference terminal, said secondary winding having a tap coupled to said reference terminal, a first capacitor coupled across said secondary winding; a second capacitor and an inductor coupled in parallel, one terminal of said inductor being coupled to said reference terminal, a third capacitor coupled between one terminal of said secondary winding and another terminal of said inductor, a crystal resonator coupled between another terminal of said secondary winding and said another terminal of said inductor; a first diode and a first resistor coupled in series between said another terminal of said inductor and said output terminal, a fourth capacitor coupled between said reference terminal and the junction between said first diode and said first resistor; a fifth capacitor, a second diode, and a second resistor coupled in series between said one terminal of said secondary winding and said output terminal, a third resistor coupled between said reference terminal and the junction between said fifth capacitor and said second diode, and a sixth capacitor coupled between said reference terminal and the junction between said second diode and said third resistor.

Claim 9

A frequency discriminator circuit comprising: an input terminal, an output terminal and a reference terminal; a transformer having a primary winding and a secondary winding, said primary winding being coupled between said input terminal and said reference terminal, said secondary winding having a tap coupled to said reference terminal, a first capacitor coupled across said secondary winding; a second capacitor and an inductor coupled in parallel, one terminal of said inductor being coupled to said reference terminal, a third capacitor coupled between one terminal of said secondary winding and another terminal of said inductor, a crystal resonator coupled between another terminal of said secondary winding and said another terminal of said inductor; a first diode and a first resistor coupled in series between said another terminal of said inductor and said output terminal, a fourth capacitor coupled between said reference terminal and the junction between said first diode and said first resistor; a fifth capacitor, a second diode, and a second resistor coupled in series between said one terminal of said secondary winding and said output terminal, a third resistor coupled between said reference terminal and the junction between said fifth capacitor and said second diode, and a sixth capacitor coupled between said reference terminal and the junction between said second diode and said third resistor.