Frequency shift keyed detector

Claim 2

A frequency shift keyed detector comprising: input signal limiter means for receiving a frequency shift keyed signal the frequency of which is to be determined, and for producing a first intermediate signal at the same frequency as said frequency shift keyed signal; bandpass filter means for passing said first intermediate signal thereby to remove the harmonics and noise outside of the pass band of said bandpass filter means from said first intermediate signal and for producing a second intermediate signal at the same frequency as said first intermediate signal; rectifying means for receiving said second intermediate signal and for producing a rectified third intermediate signal representative of the amplitude of said second intermediate signal; low pass filter means for smoothing said third intermediate signal and for producing a fourth intermediate signal representing a smoothed version of said third intermediate signal; output signal means responsive to said fourth intermediate signal for producing an output signal, said output signal being capable of assuming two different levels in response to the amplitude of said fourth intermediate signal; and means, responsive to changes in the level of said output signal, for changing the center frequency of said bandpass filter means.

Claim 3

Structure as in claim 1 iNcluding means for disabling said output signal means for a given period of time following the start of the detection process to prevent noise signals from inadvertently starting said detector circuit.

Claim 4

Structure as in claim 1 wherein said bandpass filter means is capable of having a first center frequency F1 and a second center frequency F2, wherein F2 is a higher frequency than F1.

Claim 5

Structure as in claim 3 wherein said bandpass filter means has a center frequency F1 when said output signal is high level and the center frequency F2 when said output signal is low level.

Claim 6

Structure as in claim 1 wherein said output signal means comprises means for producing first, second and third output signals, in response to changes in the frequency of said frequency shift keyed signal, said first, second and third signals controlling the center frequency of said bandpass filter means to a first, second and third center frequency respectively.

Claim 7

Structure as in claim 1 wherein said means, responsive to changes in the level of said output signal, for changing the center frequency of said bandpass filter means comprises switching means for changing the value of an impedance associated with said bandpass filter means.

Claim 8

Structure as in claim 1 wherein said bandpass filter means comprises: an operational amplifier including a positive input lead, a negative input lead and an output lead, a selected one of said input leads being connected to a reference voltage source; a first resistor connecting the other of said input leads to said output lead; a first capacitor connecting the other of said input leads to an input resistor, thereby to form a node between said first capacitor and said input resistor; a second capacitor connecting said node to said output lead; and a third resistor connecting said node to said reference voltage source.

Claim 9

Structure as in claim 7 wherein said means, responsive to changes in the level of said output signal, for changing the center frequency of said bandpass filter means comprises: a fourth resistor possessing two leads, one lead of which is connected to said node; a first transistor connected between the other lead of said fourth resistor and said reference voltage source so as to function as a switch; and means, controlled by said output signal, for turning said transistor on or off in response to the level of said output signal, thereby to effectively place said fourth resistor in parallel with said third resistor when said transistor is turned on and to remove said fourth resistor from in parallel with said third resistor when said transistor is turned off.

Claim 10

Structure as in claim 8 wherein said reference voltage source is ground and said selected one of said input leads comprises said positive input lead.

Claim 11

Structure as in claim 1 wherein said output signal means responsive to said fourth intermediate signal comprises means for producing first and second complementary output signals, said complementary output signals each being capable of assuming two different levels in response to the amplitude of said fourth intermediate signal; and said means, responsive to changes in the level of said output signal, for changing the center frequency of said bandpass filter means comprises means, responsive to changes in the level of a selected one of said first and second complementary output signals, for changing the center frequency of said bandpass filter means.

Claim 12

A frequency shift keyed detector comprising: input signal limiter means for receiving a frequency shift keyed signal, the frequency of which is to be determined, and for producing a first intermediate signal at the same frequency as said frequency shift keyed signal; bandpass filter means for passing said first intermediate signal thereby to remove the harmonics and noise outside of the passband of said bandpass filter means from said first intermediate signal and fOr producing a second intermediate signal at the same frequency as said first intermediate signals; rectifying means for receiving said second intermediate signal and for producing a rectified third intermediate signal representative of the amplitude of said second intermediate signal; low pass filter means for smoothing said third intermediate signal and for producing a fourth intermediate signal representing a smooth version of said third intermediate signal; and output signal means for producing an output signal capable of assuming a first, a second, and a third level, in response to changes in the frequency of said frequency shift keyed signal, said first, second, and third levels of said output signal controlling the center frequency of said bandpass filter means to a first, second, and third center frequency, respectively.

Claim 13

A frequency shift keyed detector comprising: input signal limiter means for receiving a frequency shift keyed signal, the frequency of which is to be determined, and for producing a first intermediate signal at the same frequency as said frequency shift keyed signal; bandpass filter means for passing said first intermediate signal thereby to remove the harmonics and noise outside of the passband of said bandpass filter means from said first intermediate signal and fOr producing a second intermediate signal at the same frequency as said first intermediate signals; rectifying means for receiving said second intermediate signal and for producing a rectified third intermediate signal representative of the amplitude of said second intermediate signal; low pass filter means for smoothing said third intermediate signal and for producing a fourth intermediate signal representing a smooth version of said third intermediate signal; and output signal means for producing an output signal capable of assuming a first, a second, and a third level, in response to changes in the frequency of said frequency shift keyed signal, said first, second, and third levels of said output signal controlling the center frequency of said bandpass filter means to a first, second, and third center frequency, respectively.

Claim 14

A frequency shift keyed detector comprising: input signal limiter means for receiving a frequency shift keyed signal, the frequency of which is to be determined, and for producing a first intermediate signal at the same frequency as said frequency shift keyed signal; bandpass filter means for passing said first intermediate signal thereby to remove the harmonics and noise outside of the passband of said passband filter means from said first intermediate signal and for producing a second intermediate signal at the same frequency as said first intermediate signal; rectifying means for receiving said second intermediate signal and for producing a rectified third intermediate signal representative of the amplitude of said second intermediate signal; low pass filter means for smoothing said third intermediate signal and for producing a fourth intermediate signal representing a smoothed version of said third intermediate signal; output signal means responsive to said fourth intermediate signal for producing an output signal capable of assuming two different levels in response to the amplitude of said fourth intermediate signal; and means for disabling said output signal means for a given period of time following the start of the detection process to prevent noise signals from inadvertently starting said detector circuit.

Claim 15

A frequency shift keyed detector comprising: input signal limiter means for receiving a frequency shift keyed signal, the frequency of which is to be determined, and for producing a first intermediate signal at the same frequency as said frequency shift keyed signal; bandpass filter means for passing said first intermediate signal thereby to remove the harmonics and noise outside of the passband of said passband filter means from said first intermediate signal and for producing a second intermediate signal at the same frequency as said first intermediate signal; rectifying means for receiving said second intermediate signal and for producing a rectified third intermediate signal representative of the amplitude of said second intermediate signal; low pass filter means for smoothing said third intermediate signal and for producing a fourth intermediate signal representing a smoothed version of said third intermediate signal; output signal means responsive to said fourth intermediate signal for producing an output signal capable of assuming two different levels in response to the amplitude of said fourth intermediate signal; and means for disabling said output signal means for a given period of time following the start of the detection process to prevent noise signals from inadvertently starting said detector circuit.

Claim 16

Structure as in claim 4 wherein said frequencies F1 and F2 correspond to the expected frequencies of said frequency shift keyed signal.