Pulse or digital communications – Systems using alternating or pulsating current – Angle modulation
Reexamination Certificate
1999-08-05
2001-10-02
Chin, Stephen (Department: 2634)
Pulse or digital communications
Systems using alternating or pulsating current
Angle modulation
C375S302000, C375S306000, C332S144000, C332S161000, C455S110000, C455S118000
Reexamination Certificate
active
06298093
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention is related in general to signal modulation, and more particularly, to apparatus and method for phase and frequency digital modulation.
BACKGROUND OF THE INVENTION
The typical digital phase and frequency modulator (PM/FM) suffers from one or more inherent performance and/or implementation limitations. One conventional approach for digital phase and frequency modulation first generates a relatively low frequency modulated signal using a low to moderate sample rate digital to analog converter (DAC) and an anti-aliasing filter. The resulting signal is then up-converted to the desired output frequency using one or more frequency translation circuits. The disadvantages of this approach are the complexity of the frequency translation circuit implementation using mixers and filters, isolation and bandwidth limitations associated with frequency translation filtering, and the presence of mixing spurious signals at the final output.
Another similar conventional implementation generates quadrature low frequency modulated signals using two digital-to-analog converters and anti-aliasing filters with a low to moderate sample rate. These signals are used to control a quadrature modulator, which directly produces the modulated output centered at the frequency of its local oscillator input. This approach provides lower complexity and wider output bandwidth capabilities than the up-conversion approach. However, the major disadvantage of this approach is that it produces distortions due to amplitude and phase imbalances which are unacceptable in many applications.
A third conventional approach uses an undersampling (or bandpass sampling) technique with a digital-to-analog converter with a moderate to high sample rate. The output signal is a sampling image which is a sum or difference of the fundamental digital-to-analog converter output frequency and a harmonic of the sampling frequency. The image is selected from all of the other images present at the digital-to-analog converter output with a bandpass filter. This approach has bandwidth limitations due to the output filtering, and dynamic range (signal-to-noise ratio) limitations of the digital-to-analog converter at output frequencies above its sample rate.
A fourth conventional implementation utilizes a very high speed digital-to-analog converter which oversamples the desired output frequency. This approach avoids the frequency conversion and filtering limitations of the other aforementioned implementations. However, spurious signals are present in the output of this implementation due to the limited resolution of the high speed digital-to-analog converter. The high levels of the spurious signals are unacceptable in many applications. The circuitry required to generate the high speed digital-to-analog converter data inputs also generally has much higher complexity and power consumption than the other approaches.
SUMMARY OF THE INVENTION
It has been recognized that it is desirable to provide apparatus and method for phase and frequency digital modulation which avoids the problems and disadvantages of conventional circuits.
In one embodiment of the invention, apparatus for phase/frequency digital modulation includes a digital circuit receiving and processing a digital modulation input signal to generate a digital modulation control signal, a digital-to-analog converter coupled to the digital circuit operable to convert the digital modulation control signal into an analog modulation control signal, and an RF/analog circuit coupled to the digital-to-analog converter. The RF/analog circuit includes a voltage controlled oscillator operable to generate a modulated output signal in response to the analog modulation control signal, and a quadrature tuner coupled to the voltage controlled oscillator operable to generate an in-phase tuner output and a quadrature tuner output in response to the modulated output signal. An analog-to-digital converter is coupled to the quadrature tuner and operable to convert the in-phase and quadrature tuner outputs to digital in-phase and quadrature tuner outputs. The digital in-phase and quadrature tuner outputs are fed back to the digital circuit to generate the digital modulation control signal.
In another embodiment of the invention, apparatus for phase/frequency digital modulation includes a programmable logic digital circuit receiving a modulation input signal and operable to generate a modulation control signal therefrom, and an RF/analog circuit coupled to the programmable logic digital circuit and receiving the modulation control signal. The RF/analog circuit includes a voltage controlled oscillator operable to generate a modulated output signal in response to the modulation control signal, and a quadrature tuner coupled to the voltage controlled oscillator operable to generate an in-phase tuner output and a quadrature tuner output in response to the modulation control signal. The in-phase and quadrature tuner outputs are fed back to the programmable logic digital circuit to generate the modulation control signal.
In yet another embodiment of the invention, a method for phase/frequency digital modulation includes the steps of receiving a modulation input signal and at least one feedback signal and generating a modulation control signal therefrom, using the modulation control signal to control a voltage controlled oscillator and generating a modulated output signal, generating an in-phase and a quadrature tuner outputs in response to the modulated output signal, and generating the at least one feedback signal from the in-phase and quadrature tuner outputs.
One technical advantage of the invention is that the use of the voltage controlled oscillator and quadrature feedback avoids the problems of frequency translation, digital-to-analog converter spurious and dynamic range, and high speed digital-to-analog converter drive circuitry complexity and power consumption. Another technical advantage of the invention is that identical RF/analog circuits enables the implementation of the digital circuit with programmable logic devices that can be configured.
REFERENCES:
patent: 4787058 (1988-11-01), Schmars
patent: 4926443 (1990-05-01), Reich
patent: 5027087 (1991-06-01), Rottinghaus
patent: 5111162 (1992-05-01), Hietala et al.
patent: 5249204 (1993-09-01), Funderburk et al.
patent: 5315620 (1994-05-01), Halawani et al.
patent: 5483203 (1996-01-01), Rottinghaus
patent: 5596609 (1997-01-01), Genrich et al.
patent: 5697068 (1997-12-01), Salvi et al.
patent: 5790601 (1998-08-01), Corrigan, III et al.
patent: 5894592 (1999-04-01), Brueske et al.
patent: 5991605 (2000-10-01), Rapeli
patent: 6028493 (2000-02-01), Olgaard et al.
patent: 6133804 (2000-10-01), Wagner et al.
patent: 196 16 368 C1 (1997-12-01), None
patent: 0 392 229 A2 (1992-03-01), None
patent: 0 889 595 A1 (1999-01-01), None
Aschwanden, Felix, Manscript, “Direct Conversion—How to Make it Work in TV Tuners”, Laboratories RCA Ltd., Badenestrasse 569, CH 8048, Zurich, Switzerland, IEEE Transactions on Consumer Electronics, vol. 42, No. 3, Aug. 1996, pp. 729-738.
PCT International Search Report dated Nov. 10, 2000 for PCT/US 00/20060 filed Jul. 21, 2000.
Hogenauer, Eugene B., Manuscript: “An Economical Class of Digital Filters for Decimation and Interpolation”, IEEE Transactions on Acoustics, Speech and Signal Processing, vol. ASSP-29, No. 2, Apr. 1981, 9 pages.
PCT International Search Report dated Nov. 15, 2000 for PCT/US 00/21016 filed Aug. 1, 2000.
Baker & Botts L.L.P.
Chin Stephen
Ha Dac V.
Raytheon Company
LandOfFree
Apparatus and method for phase and frequency digital modulation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for phase and frequency digital modulation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for phase and frequency digital modulation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2562479