Two-port synthesizer modulation system employing an improved reference phase modulator

Claim 2

An improved two-port frequency modulating apparatus for a phase-locked loop frequency synthesizer, comprising in combination: an unmodulated reference source including an oscillator and a fixed-integer frequency divider; a phase detector having a first input coupled to said reference source and an output coupled to a loop filter; a direct-FM VCO having an input port for coupling a modulating signal and the loop filter thereto and having an output with a feedback path coupled to a second input of said phase detector and including a selectable-integer frequency divider; and a modified frequency modulator, having an input port for the modulating signal and including an integrator and a low-noise phase modulator, said modified frequency modulator interposed between said unmodulated reference source and said phase detector and exhibiting a flat, wide, modulation bandwidth, down to less than 1 Hertz, which effectively cancels the modulation components induced by the direct-FM VCO, thereby providing a modulation bandwidth for the frequency synthesizer which is nearly equal to the theoretical maximum available bandwidth.

Claim 3

The arrangement according to claim 1, wherein said modified frequency modulator includes an integrator and a low-noise serrasoid phase modulator.

Claim 4

The frequency modulating arrangement according to claim 1, wherein said low-noise phase modulator comprises: a comparator having a first terminal for inputting a modulating signal; a capacitor having a first terminal connected to ground and a second terminal coupled to a second input of said comparator; an electronic switch having first and second terminals coupled to the first and second terminals of said capacitor, and a third terminal for inputting a reference signal; and passive current source means coupled to the second terminal of said capacitor and including a filter section and a current-limiting section.

Claim 5

The two-port frequency modulating arrangement according to claim 1, wherein the low-noise phase modulator includes a passive current source having a filter section comprising a series combination of a first resistor and a capacitor, with a first terminal of the capacitor connected to ground and a first terminal of the first resistor connected to a constant supply voltage, and a second terminal of each of the resistor and the capacitor coupled to a current-limiting section comprising at least one resistor significantly larger in value than said first resistor.

Claim 8

The method according to claim 5, wherein the step of producing a high stability unmodulated reference signal comprises generating a high frequency signal having high stability and then dividing the frequency thereof by an integer to produce said predetermined frequency.

Claim 9

The method according to claim 5, wherein the step of feeding back a portion of the generated output signal comprises dividing the frequency of said output signal by a selected integer.

Claim 10

The method according to claim 5, wherein he step of detecting the phase difference includes a further step of filtering the output correction signal to maintain the voltage controlled oscillator at a desired frequency.

Claim 11

The method according to claim 5, wherein the step of introducing modulation into the second port comprises integrating and then phase modulating the predetermined frequency of said high stability unmodulated reference signal in a low-noise phase modulator before the step of detecting a phase difference.

Claim 12

An improved two-port frequency modulating arrangement for a phase-locked loop frequency synthesizer, comprising in combination: unmodulated reference source means; means for phase detecting having a first input coupled to said unmodulated reference source means and an output coupled to an included loop filtering means; direct-FM VCO means having an input port for coupling a modulating signal and the loop filter thereto and having an output which couples to an included selectable-integer frequency dividing means in a feedback path to a second input of said phase detecting means; and

Claim 13

An improved two-port frequency modulating arrangement for a phase-locked loop frequency synthesizer, comprising in combination: unmodulated reference source means; means for phase detecting having a first input coupled to said unmodulated reference source means and an output coupled to an included loop filtering means; direct-FM VCO means having an input port for coupling a modulating signal and the loop filter thereto and having an output which couples to an included selectable-integer frequency dividing means in a feedback path to a second input of said phase detecting means; and

Claim 14

a modified frequency modulator having an input port for the modulating signal and interposed between said unmodulated reference source means and said phase detecting means, said modified frequency modulator exhibiting a flat, wide, modulation bandwidth, down to at least 1 Hertz, which effectively cancels modulation components induced by the direct-FM VCO, thereby providing a modulation bandwidth for the frequency synthesizer which is nearly equal to the theoretical maximum available bandwidth.

Claim 15

a modified frequency modulator having an input port for the modulating signal and interposed between said unmodulated reference source means and said phase detecting means, said modified frequency modulator exhibiting a flat, wide, modulation bandwidth, down to at least 1 Hertz, which effectively cancels modulation components induced by the direct-FM VCO, thereby providing a modulation bandwidth for the frequency synthesizer which is nearly equal to the theoretical maximum available bandwidth.

Claim 16

The apparatus according to claim 10, wherein said unmodulated reference source means includes an oscillator and a fixed-integer frequency divider.

Claim 17

The apparatus according to claim 10, wherein said phase detecting means includes a sample-and-hold phase detector.

Claim 18

The apparatus according to claim 10, wherein said phase detecting means includes a charge pump type of phase detector.

Claim 19

The apparatus according to claim 10, wherein said direct-FM VCO means comprises a direct-FM VCO having a first input coupled to said loop filter for generally controlling the center frequency of said VCO and a second input having lesser sensitivity for frequency modulating said VCO about its center frequency.

Claim 20

The apparatus according to claim 10, wherein said low-noise phase modulator includes a low-noise serrasoid phase modulator comprising a comparator and a voltage ramp generator having a capacitive storage element with a first terminal coupled to one input of said comparator and a second terminal connected to ground, and an electronic switch having first and second terminals connected to respective terminals of said capacitive storage element as well as having a third terminal for inputting a reference signal, and a passive current source which exhibits low noise coupled to the second terminal of said capacitive storage element.

Claim 21

The apparatus according to claim 15, wherein said passive current source comprises: a filter section having a series combination of a first resistor and a capacitor with a first terminal of the capacitor connected to ground and a first terminal of the resistor connected to a constant supply voltage; and a current-limiting section, coupled to a second terminal of each of the first resistor and the capacitor of said filter section, including a second resistor which is approximately one order of magnitude larger than said first resistor interposed between said filter section and said capacitive storage element.

Claim 22

A low-noise phase modulator apparatus, comprising in combination: comparator means having a first input coupled to a modulating input signal; a capacitive storage element with a first terminal coupled to a second input of said comparator and its second terminal connected to common ground; an electronic switch with first and second terminals coupled to the respective terminals of said capacitive storage element and with a third terminal coupled to a reference frequency for providing control thereof; and a passive current source, including a filter section and a current-limiting section, coupled between a supply voltage and said second terminal of the comparator, said a passive current source providing reduced low frequency noise and cooperating with said electronic switch to provide a nearly linear ramp voltage on said capacitive storage element.

Claim 23

A low-noise phase modulator apparatus, comprising in combination: comparator means having a first input coupled to a modulating input signal; a capacitive storage element with a first terminal coupled to a second input of said comparator and its second terminal connected to common ground; an electronic switch with first and second terminals coupled to the respective terminals of said capacitive storage element and with a third terminal coupled to a reference frequency for providing control thereof; and a passive current source, including a filter section and a current-limiting section, coupled between a supply voltage and said second terminal of the comparator, said a passive current source providing reduced low frequency noise and cooperating with said electronic switch to provide a nearly linear ramp voltage on said capacitive storage element.

Claim 24

The low-noise phase modulator according to claim 17, wherein said passive current source comprises a filter section having a first resistor and a capacitor coupled in series between said supply voltage and common ground and a current-limiting section comprising a second resistor approximately one order of magnitude greater than said first resistor interposed between said filter section and said capacitive storage element so as to provide a nearly constant current to said capacitive storage element.

Claim 25

An improved two-port frequency modulating apparatus for a phase-locked loop frequency synthesizer which has a relatively low frequency RF carrier with relatively high percentage deviation frequency modulation at its output, comprising in combination: unmodulated reference source means; phase detecting means having a first input coupled to said reference source means and an output coupled to included loop filtering means; direct-FM VCO means having an input port for coupling a modulating signal and the loop filtering means thereto and having an output which coupled to an included selectable-integer frequency dividing means in a feedback path to a second input of said phase detecting means; offset mixing means having a first input coupled to said direct-FM VCO means and a second input coupled through multiplying means to said unmodulated reference source; and a modified frequency modulator having an input port for the modulating signal and including an integrator and a low-noise phase modulator, said modified frequency modulator interposed between said unmodulated reference source means and said phase detecting means and exhibiting a flat, wide, modulation bandwidth, down to at least 1 Hertz, which effectively cancels modulation components induced by said direct-FM VCO means, and said offset mixing means for down mixing the output of said direct-FM VCO means, thereby providing a relatively low frequency RF output carrier with relatively large percentage deviation and providing a modulation bandwidth for the frequency synthesizer which is nearly equal to the theoretical maximum available bandwidth.

Claim 26

An improved two-port frequency modulating apparatus for a phase-locked loop frequency synthesizer which has a relatively low frequency RF carrier with relatively high percentage deviation frequency modulation at its output, comprising in combination: unmodulated reference source means; phase detecting means having a first input coupled to said reference source means and an output coupled to included loop filtering means; direct-FM VCO means having an input port for coupling a modulating signal and the loop filtering means thereto and having an output which coupled to an included selectable-integer frequency dividing means in a feedback path to a second input of said phase detecting means; offset mixing means having a first input coupled to said direct-FM VCO means and a second input coupled through multiplying means to said unmodulated reference source; and a modified frequency modulator having an input port for the modulating signal and including an integrator and a low-noise phase modulator, said modified frequency modulator interposed between said unmodulated reference source means and said phase detecting means and exhibiting a flat, wide, modulation bandwidth, down to at least 1 Hertz, which effectively cancels modulation components induced by said direct-FM VCO means, and said offset mixing means for down mixing the output of said direct-FM VCO means, thereby providing a relatively low frequency RF output carrier with relatively large percentage deviation and providing a modulation bandwidth for the frequency synthesizer which is nearly equal to the theoretical maximum available bandwidth.

Claim 27

The apparatus according to claim 19, wherein said unmodulated reference source means includes an oscillator and a fixed-integer frequency divider.

Claim 28

The apparatus according to claim 19, wherein said phase dectecting means includes a sample-and-hold phase detector.

Claim 29

The apparatus according to claim 19, wherein said phase detecting emans includes a charge pump type of phase detector.

Claim 30

The apparatus according to claim 19, wherein said direct-FM VCO means comprises a direct-FM VCO having a first input coupled to said loop filter for generally controlling the center frequency of said VCO and a second input of lesser sensitivity for frequency modulating said VCO about its center frequency.

Claim 31

The apparatus according to claim 19, wherein said low-noise phase modulator includes a low-noise serrasoid phase modulator comprising a comparator and a voltage ramp generator having a capacitive storage element with a first terminal coupled to one input of said comparator and a second terminal connected to ground, and an electronic switch having first and second terminals connected to respective terminals of said capacitive storage element as well as having a third terminal for inputting a reference signal, and a passive current source which exhibits low noise coupled to the second terminal of said capacitive storage element.

Claim 32

The apparatus according to claim 19, wherein said passive current source comprises: a filter section having a series combination of a first resistor and a capacitor with a first terminal of the capacitor connected to ground and a first terminal of the resistor connected to a constant supply voltage; and a current-limiting section, coupled to a second terminal of each of the first resistor and the capacitor of said filter section, including a second resistor which is approximately one order of magnitude larger than said first resistor interposed between said filter section and said capacitive storage element.