Modulators – Amplitude modulator – Plural modulation
Reexamination Certificate
2001-12-14
2003-11-25
Mis, David C. (Department: 2817)
Modulators
Amplitude modulator
Plural modulation
C455S102000
Reexamination Certificate
active
06653909
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to radio transmitters for transmitting radio signals which vary in amplitude as well as in phase or frequency.
From the article: Asad A. Abidi: “Low-Power Radio-Frequency ICs for Portable Communications”, Proceedings of the IEEE, Vol. 83 No. 4, April 1995, pp. 544-569, radio transmitters are known, for example in mobile telephones, where signals representing a desired transmitted radio signal are processed in a Digital Signal Processor and delivered from the processor to a transmitter radio frequency (RF) output unit as digital signals in quadrature form; compare for example FIG. 13.
It is a disadvantage in the transmitters thus known that the non-linearities of the power amplifier distort the transmitted signal.
From the article: V. Petrovic: “Reduction of Spurious Emission from Radio Transmitters by Means of Modulation Feedback”, IEE Conference on Radio Spectrum Conservation Technique, September 1983, pp. 44-49, a Single-Sideband (SSB) Radio Transmitter is known, in which two output quadrature signals are generated from the output RF signal, and two input quadrature signals are generated from an input signal as well. The quadrature output signals are demodulated by two quadrature carrier signals generated digitally, and are fed back and compared with the input quadrature signals. Difference quadrature signals are amplified and modulated with the carrier signals and summed to form the output RF signal.
It is a disadvantage in this known transmitter that the input quadrature signals are generated from a complete, modulated input signal by means of a phase-shift circuit. The article mentions the difficulties experienced when designing a reliable wide-band 90° phase-shift network.
From the article: Hiroaki Kosugi et al.: “A High-Efficiency Linear Power Amplifier Using an Envelope Feed-Back Method”, Electronics and Communication in Japan, Part 2, Vol. 77, No. 3, 1994, pp. 50-57, a Power Amplifier is known, in which input signals are fed to a power amplifier in quadrature form, that is generated by a quadrature mixer not specified in detail. An envelope signal is derived mathematically from the input quadrature signals, and is used as independent variable in an envelope feed-back loop controlling the envelope of the power output signal. No phase feed-back is disclosed.
It is a disadvantage in this known amplifier that the phase distortion of the power amplifier is not controlled or overcome.
From the article: Leonard R. Kahn: “Single-Sideband Transmission by Envelope Elimination and Restoration”, Proceedings of the I.R.E., 1952, pp. 803-806, an SSB Transmitter is known, wherein the phase and the amplitude components of an input signal are separated and amplified independently before being combined in a final output stage.
It is a serious disadvantage in this transmitter that modulating the amplitude at a high power level tends to generate considerable amounts of spurious signals.
From the article: V. Petrovic & W. Gosling: “Polar-Loop Transmitter”, Electronics Letters, 10 May 1979 Vol. 15 No. 10, pp. 286-288, a Polar Modulation Feedback Linearisation System for an SSB Transmitter is known, wherein the modulated output from a Radio Frequency Power Amplifier (RF PA) is being controlled by means of two closed loops, each having the same modulated Intermediate Frequency (IF) Signal as the controlling variable. A first loop controls the Amplitude Modulation (AM) or the “envelope” of the RF output signal relative to the IF signal, and a second loop controls the Phase Modulation (PM) of the RF output signal relative to the IF signal. Polar representation of the RF signal vector is used in the article, the vector angle representing the signal phase and the vector magnitude representing the signal amplitude.
Thus, this polar modulation feedback linearization system uses a fully modulated IF signal which is demodulated into an amplitude signal and a phase signal, respectively. It is a disadvantage that the analog control signals for the amplitude and phase loops thus have to be extracted from the IF signal.
SUMMARY OF THE INVENTION
The invention provides a digital signal set containing amplitude as well as phase or frequency modulation information, the signal set enabling transfer of this information from a digital domain to an analog domain in an efficient way, the signals being comparatively easily generated in the digital domain and at the same time being suited for conversion into an analog signal set in a way reducing efficiently the risk of “cross-talk” between the amplitude modulation and the phase or frequency modulation, and enabling a very efficient linearisation of a simple and energy-efficient analog output stage in a radio transmitter.
The invention provides a set of digital signals; a radio transmitter; and a method for transforming modulation information from a digital signal processing system into analog signals for controlling analog modulator and amplifier circuitry.
In a digital signal set containing amplitude as well as phase or frequency modulation information for compound modulating a carrier wave, the set comprises the following three digital signals:
a first and a second digital signal representing a desired phase angle of the carrier wave; and
a third digital signal representing a desired amplitude of the carrier wave.
Hereby, modulation information is provided which is suitable for driving particularly simple modulator circuits while obtaining high quality modulation with a minimum of cross-talk between the different types of modulation, while the information is still simple to establish in a digital signal processing system.
Cross-talk between the amplitude and phase or frequency modulation, respectively, is primarily being avoided due to the fact that the amplitude modulation information and the phase or frequency modulation information, respectively, are separated from one another in the digital domain, such that the digital-to-analog conversion may be made on the separated modulation information signals rather than on a compound signal containing both types of modulation information. Retrieval of the two types of modulation information from one and the same compound analog signal of the prior art will not be possible with state-of-the-art analog circuitry without the use of very elaborate and expensive circuits.
It is preferred that the first and second digital signals correspond to each their component of a desired phase unit vector in a Cartesian coordinate system.
Hereby, phase or frequency information is provided which is particularly suited for being transformed into analog phase or frequency information in a simple modulator circuit.
The invention provides a method for amplitude and phase or frequency modulating an output signal from an amplifier circuit such as a radio transmitter output stage, the method permitting efficient and component-saving use of contemporary digital signal processing systems together with analog aerial output circuitry and at the same time eliminating the disadvantages of the prior art.
A method for transforming modulation information from a digital signal processing system into analog signals suitable for controlling analog modulator and amplifier circuitry, the information comprising amplitude modulation information as well as phase or frequency modulation information for compound modulating a carrier wave, comprises the steps of:
providing a first and a second digital signal representing a desired phase angle of the carrier wave;
converting each of the first and second digital signals into corresponding first and second analog signals;
mixing the first and second analog signals with first and second oscillator signals to obtain an analog, phase or frequency modulated signal;
providing a third digital signal corresponding to the desired amplitude of the carrier wave;
converting the third digital signal into a corresponding analog amplitude signal; and
feeding the analog phase or frequency modulated signal and the analog amplitude signal to said analog mod
No associations
LandOfFree
Digital signals, radio transmitter circuits and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Digital signals, radio transmitter circuits and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Digital signals, radio transmitter circuits and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3176233