Amplifiers – Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
1998-11-18
2001-02-27
Mottola, Steven J. (Department: 2817)
Amplifiers
Hum or noise or distortion bucking introduced into signal...
C332S145000
Reexamination Certificate
active
06194963
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to RF amplifiers and, more particularly, to a circuit and method having I/Q modulation and independent amplitude modulation in a power amplifier.
BACKGROUND OF THE INVENTION
Radio frequency (RF) transmitters, such as used in cellular telephones, develop an RF signal to be transmitted through the air. Information is carried on the signal via some form of modulation such as frequency modulation, phase modulation, amplitude modulation, or a combination of these.
It may be desirable to create a modulated signal with both amplitude and phase modulation. With the necessity of developing small and lightweight devices, particularly cellular telephones, it is important that such amplifier circuits use a minimum of components. One way to satisfy this desire is to directly modulate an oscillator phase lock loop (PLL) to impart the phase modulation component directly on the signal and then to amplitude modulate the power amplifier stage connected to a voltage controlled oscillator/phase lock loop (VCO/PLL) combination with the amplitude component. VCO/PLL circuits exist that have sufficient bandwidth relative to the information bandwidth of the signal to cause the phase modulation to occur directly on the output signal without any up-conversion. It remains, however, to put an amplitude signal onto this phase modulated signal. This is preferably done in the power amplifier stage, as it will permit this stage to run at high efficiency in a non-linear mode. A difficulty might arise in that the information bandwidth of the individual phase modulation component of the signal is larger than that of the composite signal. For complex quadrature amplitude modulation (QAM) signals, the PLL loop bandwidth may not be sufficient to impart all of the phase modulation components of the spectrum.
Previously, the above problem has been solved by direct I/Q modulation of the RF signal applying both amplitude and phase modulation to the RF signal. This requires a linear power amplifier to follow the I/Q modulator. A problem with the linear power amplifier is that it has an efficiency only in the range of thirty to forty percent and generates more heat than power.
The present invention is directed to overcoming one or more of the problems discussed above in a novel and simple manner.
SUMMARY OF THE INVENTION
In accordance with the invention there is provided a circuit and method independently controlling amplitude and phase modulation in an RF amplifier circuit.
Broadly, there is disclosed herein an RF amplifier including a phase modulator developing a phase modulated RF input signal to be transmitted. A power amplifier receives the RF input signal and amplifies the RF input signal to develop an RF output signal. An amplifier control is operatively associated with the the power amplifier. The amplifier control includes means for developing a control signal representing a desired amplitude of the RF output signal. Memory means store correction information correlating actual amplitude of the RF output signal relative to the control signal. Control means vary the power amplifier supply voltage using the control signal modified responsive to the correction information for the desired amplitude.
It is a feature of the invention that the phase modulator comprises an I/Q modulator. The phase modulator has no amplitude modulation.
It is another feature of the invention that the amplifier control comprises a processor.
It is still another feature of the invention that the memory means stores a transfer curve of the power amplifier RF output signal relative to the control signal.
It is still another feature of the invention to provide means coupled to the amplifier control for monitoring the RF output signal. The amplifier control periodically updates the correction information using the monitored RF output signal.
It is still another feature of the invention that the control means comprises a switching regulator developing the power amplifier supply voltage. Alternatively, the control means comprises a delta-sigma modulator, Class D amplifier stage and a low pass filter developing the power amplifier circuit supply voltage.
It is still a further feature of the invention that the control means comprises a programmed processor controlling the phase modulator. The phase modulator uses a high speed phase lock loop (PLL). The PLL includes a voltage-controlled oscillator (VCO) and a divider in a control loop for the VCO and the processor, in the form of a delta-sigma modulator, controls the divider integer to set channel frequency.
In accordance with another aspect of the invention an RF amplifier includes an I/Q modulator developing a phase modulated RF input signal to be transmitted. A power amplifier receives the RF input signal and amplifies the RF input signal to develop an RF output signal. An amplifier control is operatively associated with the I/Q modulator and the power amplifier, the amplifier control driving the I/Q modulator to impart phase modulation and varying the power amplifier supply voltage to linearize amplitude modulation in the power amplifier circuit.
In accordance with a further aspect of the invention there is disclosed the method of linearizing amplitude modulation in a power amplifier of an amplifier circuit comprising the steps of developing a phase modulated RF input signal to be transmitted, a power amplifier receiving the RF input signal and amplifying the RF input signal to develop an RF output signal, storing correction information correlating actual amplitude of the RF output signal relative to an amplifier control signal, and varying the power amplifier supply voltage using the amplitude control signal modified responsive to the correction information for the desired amplitude.
Further features and advantages of the invention will be readily apparent from the specification and from the drawing.
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Arpaia Domenico
Boesch Ronald D.
Camp, Jr. William O.
Gore Charles
Schlang Jeffrey A.
Ericsson Inc.
Mottola Steven J.
Wood Phillips VanSanten Clark & Mortimer
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