Modulators – Phase shift keying modulator or quadrature amplitude modulator
Reexamination Certificate
1998-12-10
2001-03-13
Kinkead, Arnold (Department: 2817)
Modulators
Phase shift keying modulator or quadrature amplitude modulator
C332S145000, C330S010000, C330S12400D, C375S298000, C375S300000, C363S043000
Reexamination Certificate
active
06201452
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to modulation systems and methods and more particularly to systems and methods that can efficiently modulate a signal onto a radio frequency carrier.
BACKGROUND OF THE INVENTION
Modulation systems and methods are widely used in transmitters to modulate information including voice and/or data onto a carrier. The carrier may be a final carrier or an intermediate carrier. The carrier frequency can be in UHF, VHF, RF, microwave or any other frequency band. Modulators are also referred to as “mixers” or “multipliers”. For example, in a mobile radiotelephone, a modulator is used in the radiotelephone transmitter.
In modern radiotelephone communications, mobile radiotelephones continue to decrease in size, cost and power consumption. In order to satisfy these objectives, it is generally desirable to provide modulation systems and methods that can provide high power modulation while reducing the amount of battery power that is consumed. Unfortunately, the power amplifier of a modulator may consume excessive power due to efficiency limitations therein. More specifically, it is known to provide linear Class-A or Class-AB power amplifiers that may have efficiencies as low as 30% or less. Thus, large amounts of battery power may be wasted as heat.
In modulation systems and methods, it is known to provide a desired modulation of a radio signal as a stream of complex numbers including a real part and an imaginary part. Such a stream of complex numbers may be generated by a digital signal processor in a radiotelephone. Systems and methods for modulating a stream of complex numbers are described in U.S. Pat. No. 5,815,531 to the present co-inventor Dent entitled “Transmitter for Encoded Data Bits”, assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference.
As described in the '531 patent, Quadrature Amplitude Modulated signals are generated from data bits by using a first Quadrature Phase Shift Keying (QPSK) modulator for encoding a first pair of the data bits into one of four carrier signal phases, thereby producing a first QPSK signal. A second QPSK modulator encodes a second pair of the data bits into one of four carrier signal phases, thereby producing a second QPSK signal. The first QPSK signal is amplified to a first power level, and the second QPSK signal is amplified to a second power level. The first and second amplified signals are then combined to produce a signal in which four data bits are encoded. Offset Quadrature Phase Shift Keying (OQPSK) may be used in place of the first and second QPSK modulators, so that an Offset Quadrature Amplitude Modulation (OQAM) transmitter is formed. An OQPSK modulator encodes data bits by encoding a first sub-group of the data bits into a real part of a complex signal at an odd instant of a clock, and by encoding a second sub-group of the data bits into an imaginary part of the complex signal at an even instant of the clock. OQPSK modulation provides the benefit of having all signal transitions being constrained to trajectories around constant radius circles, thereby producing spectral efficiency. See the '531 patent abstract.
Notwithstanding the improvements of the above described patent, there continues to be a need for improved methods and systems for converting a stream of complex numbers representing a desired modulation of a radio signal into a modulated radio power signal at a radio carrier frequency. Preferably, these systems and methods can perform conversion at high efficiencies so that the size, cost and/or power consumption of the modulation system may be reduced.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide improved modulation systems and methods.
It is another object of the present invention to provide modulation systems and methods that can provide high efficiency.
It is yet another object of the present invention to provide modulation systems and methods that can modulate a stream of complex numbers representing a desired modulation of a radio signal, at high efficiency.
These and other objects are provided, according to the present invention, by representing a real part of each of the complex numbers in a stream of complex numbers representing a desired modulation of a radio signal, as a plurality of first digits of decreasing numerical significance and representing an imaginary part of each of the complex numbers as a plurality of second digits of decreasing numerical significance. A respective one of the first digits and a respective one of the second digits of like numerical significance are grouped to form a plurality of phase control symbols. A respective phase control symbol is then used to control the phase of an output signal at the radio carrier frequency from a respective one of the plurality of power amplifiers. Each of the power amplifiers provides an output power level that is related to the numerical significance of the first and second digits that form the associated phase control symbol. The output power levels of the plurality of power amplifiers are combined to thereby form the modulated radio power signal.
Preferably, the digits are binary digits such that each of the phase control symbols is one of four values. The power amplifiers are preferably saturated power amplifiers that produce a constant radio frequency voltage output. More preferably, the power amplifiers are bilateral power amplifiers that allow current to flow from and to an amplifier power supply.
The output levels of the plurality of power amplifiers may be combined using various techniques. For example, a respective output power level may be applied to a primary winding of a respective one of a plurality of transformers, the secondary windings of which are serially coupled to produce the modulated radio power signal. Alternatively, a respective output power level may be applied to a respective quarter wave transmission line, and the quarter wave transmission lines may be coupled to one another to produce the modulated radio power signal. In yet another alternative, at least two of the phase control signals of the least numerical significance may be coupled to at least one linear amplifier to produce a linear output. The linear output and the output power levels of the plurality of power amplifiers may then be combined to form the modulated radio power signal.
According to another aspect of the present invention, a real part of each of the complex numbers is represented as a plurality of first digits of decreasing numerical significance and an imaginary part of each of the complex numbers is represented as a plurality of second digits of decreasing numerical significance. A plurality of phase modulators is provided, a respective one of which is responsive to a respective one of the plurality of first digits and a respective one of the plurality of second digits of like numerical significance, and to the radio carrier frequency, to produce a phase modulated output at the radio carrier frequency. A plurality of power amplifiers is provided, a respective one of which amplifies a respective one of the phase modulated outputs of the phase modulators to an amplifier power level at an output thereof. A combining circuit combines the outputs of the power amplifiers according to a combining ratio to produce the modulated radio power signal. Either the amplifier output level or the combining ratio or both are selected such that the modulated radio power signal is related to the numerical significance of the plurality of first and second digits.
In a first embodiment, each of the power amplifiers produces the same amplifier output level and the combining ratio is selected such that the outputs of the power amplifiers are combined according to a ratio that is related to the numerical significance of the digits that are associated with the respective power amplifier. In another alternative, the combining ratio is unity and the amplifier output level of a respective power amplifier is related to the numer
Camp, Jr. William O.
Dent Paul W.
Holden Alan R.
Ericsson Inc.
Kinkead Arnold
Myers Bigel & Sibley & Sajovec
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