Full threshold FM deviation compression feedback demodulator and method

Claim 2

A FM demodulator utilizing FM deviation compression feedback comprising: a local oscillator supplying local oscillations; a mixer means having an input receiving an FM signal of prescribed FM deviation and an input receiving said local oscillations and converting said FM signal to a converted IF output signal having a prescribed reduced FM deviation; an IF amplifier comprising at least one stage coupled to said mixer means output signal for amplifying and selective filtering of said converted IF signal output within a prescribed bandwidth; a means for coupling an output of said IF amplifier to an FM demodulator, and providing a demodulated output signal to an output terminal of said FM demodulator; and a feedback loop delivering a feedback signal from said output terminal of said FM demodulator to an input of said oscillator for controlling said mixing in said mixer means in a manner as to track said FM signal of prescribed FM deviation, wherein said feedback loop comprises a filter means for reducing said feedback signal at higher demodulation frequencies and increasing said feedback signal at lower demodulation frequencies, thereby reducing the FM deviation of said converted IF signal to the prescribed reduced FM deviation.

Claim 3

A FM demodulator as recited in claim 1, in which said IF amplifier is controlled by a bandwidth control.

Claim 4

A FM demodulator as recited in claim 1, in which said filter means includes a variable loop filter.

Claim 5

A FM demodulator as recited in claim 3, in which said variable loop filter is controlled by a bandwidth control.

Claim 6

A FM demodulator as recited in claim 1, in which the said IF amplifier comprises a limiter.

Claim 7

A FM demodulator as recited in claim 1, in which the said IF amplifier comprises means responsive to signal strength of at least one converted IF signal providing an output signal.

Claim 10

A FM demodulator utilizing FM deviation compression feedback comprising: a first mixer means, comprising an input receiving a FM signal of prescribed FM deviation and an input receiving first local oscillations, for converting the FM signal to a first converted IF signal having a first prescribed reduced FM deviation; a first local oscillator supplying said first local oscillations to said first mixer means and having an output terminal and an input terminal; a first IF amplifier comprising at least one stage coupled to said first mixer means output for amplifying and selective filtering of said first converted IF signal to within a first prescribed bandwidth, and having an output terminal and an input terminal; a second mixer means, comprising an input terminal coupled to the output terminal of the first IF amplifier and an input receiving second local oscillations, for converting the amplified and selectively filtered first converted IF signal to a second converted IF signal which has a second prescribed reduced FM deviation lower than said first prescribed reduced FM deviation; a second local oscillator supplying said second local oscillations to said second mixer means, and having an output terminal and an input terminal; a second IF amplifier comprising at least one stage coupled to the output terminal of said second mixer means for amplifying and selectively filtering of said second converted IF signal to within a second prescribed bandwidth; a means for coupling said converted IF signal to an FM demodulator, and providing a demodulated output signal to an output terminal of said FM demodulator; a first feedback loop coupling said output terminal of said FM demodulator back to said input terminal of said first local oscillator for controlling said first local oscillations, thereby reducing the FM deviation of said received input FM signal of prescribed FM deviation to said first prescribed reduced FM deviation of the converted first IF signal; a second feedback loop coupling said output terminal of said FM demodulator back to said input terminal of said second local oscillator for controlling said second local oscillations, thereby reducing the FM deviation of the amplified and selectively filtered first converted IF signal to the second prescribed reduced FM deviation, wherein at least one of said first and second feedback loops comprises a filter means for reducing said feedback signal at higher demodulation frequencies and increasing said feedback signal at lower demodulation frequencies.

Claim 11

A FM demodulator utilizing FM deviation compression feedback comprising: a first mixer means, comprising an input receiving a FM signal of prescribed FM deviation and an input receiving first local oscillations, for converting the FM signal to a first converted IF signal having a first prescribed reduced FM deviation; a first local oscillator supplying said first local oscillations to said first mixer means and having an output terminal and an input terminal; a first IF amplifier comprising at least one stage coupled to said first mixer means output for amplifying and selective filtering of said first converted IF signal to within a first prescribed bandwidth, and having an output terminal and an input terminal; a second mixer means, comprising an input terminal coupled to the output terminal of the first IF amplifier and an input receiving second local oscillations, for converting the amplified and selectively filtered first converted IF signal to a second converted IF signal which has a second prescribed reduced FM deviation lower than said first prescribed reduced FM deviation; a second local oscillator supplying said second local oscillations to said second mixer means, and having an output terminal and an input terminal; a second IF amplifier comprising at least one stage coupled to the output terminal of said second mixer means for amplifying and selectively filtering of said second converted IF signal to within a second prescribed bandwidth; a means for coupling said converted IF signal to an FM demodulator, and providing a demodulated output signal to an output terminal of said FM demodulator; a first feedback loop coupling said output terminal of said FM demodulator back to said input terminal of said first local oscillator for controlling said first local oscillations, thereby reducing the FM deviation of said received input FM signal of prescribed FM deviation to said first prescribed reduced FM deviation of the converted first IF signal; a second feedback loop coupling said output terminal of said FM demodulator back to said input terminal of said second local oscillator for controlling said second local oscillations, thereby reducing the FM deviation of the amplified and selectively filtered first converted IF signal to the second prescribed reduced FM deviation, wherein at least one of said first and second feedback loops comprises a filter means for reducing said feedback signal at higher demodulation frequencies and increasing said feedback signal at lower demodulation frequencies.

Claim 12

A FM demodulator as recited in claim 8, in which the first and second IF amplifiers comprise means responsive to signal strength of at least one converted IF signal providing an output signal.

Claim 13

A FM demodulator as recited in claim 8, wherein a second frequency compensation network is interposed between the FM demodulator and the second local oscillator.

Claim 14

A FM demodulator as recited in claim 10, wherein said second frequency compensation network is a second variable loop filter.

Claim 15

A FM demodulator as recited in claim 8, in which said first local oscillator provides means for band switching or band tuning.

Claim 16

A FM demodulator as recited in claim 10, wherein a first frequency compensation network is interposed between the second frequency compensation network and the input terminal of said first local oscillator.

Claim 17

A FM demodulator as recited in claim 13, wherein said first frequency compensation network is a first variable loop filter.

Claim 18

A FM demodulator as recited in claim 14, having a bandwidth control for controlling said IF amplifiers and said first loop filter in a fashion as to reduce said demodulation bandwidth to a prescribed reduced demodulation bandwidth.

Claim 19

A FM demodulator as recited in claim 1, including means for detecting said received signal condition and evaluating said detected signal providing a bandwidth control signal.

Claim 20

A FM demodulator as recited in claim 1, wherein said filter means causes a deviation slope in the IF amplifier.

Claim 21

A FM demodulator as recited in claim 1, wherein said filter means comprises a proportional-plus-integral-type filter.

Claim 22

A method of demodulating a FM signal as recited in claim 7, further comprising the step of de-emphasizing said demodulated IF signal by passing said demodulated signal through said proportional-plus-integral-type filter.

Claim 23

A FM demodulator as recited in claim 13, wherein said first frequency compensation network comprises a proportional-plus-integral-type filter.

Claim 24

A FM demodulator as recited in claim 10, wherein said second frequency compensation network comprises a proportional-plus-integral-type filter.

Claim 25

A method of demodulating a FM signal as recited in claim 7, wherein said loop filter is a variable loop filter.

Claim 26

A FM demodulator as recited in claim 11, having a bandwidth control for controlling said IF amplifiers and said second loop filter in a fashion as to reduce said demodulation bandwidth to a prescribed reduced demodulation bandwidth.