Amplifiers – Modulator-demodulator-type amplifier
Reexamination Certificate
1999-01-07
2001-01-30
Pascal, Robert (Department: 2817)
Amplifiers
Modulator-demodulator-type amplifier
C330S149000
Reexamination Certificate
active
06181199
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to modulation systems and methods, and more particularly to IQ modulation systems and methods.
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 for the radiotelephone transmitter.
FIG. 1
illustrates a conventional IQ modulator. As shown in
FIG. 1
, an IQ modulator
10
, also referred to as a “quadraphase modulator” or a “quadrature modulator” includes a quadrature splitter
20
, also known as a 90° phase shifter, and a pair of multipliers
16
a
,
16
b
coupled to the quadrature splitter. A controlled oscillator
15
, such as a Voltage Controlled Oscillator (VCO), is coupled to the quadrature splitter
20
to produce 90° phased shifted oscillator signals. In-phase (I) data
11
a
and quadrature-phase (Q) data
11
b
are coupled to a respective multiplier or mixer
16
a
,
16
b
. Digital input data is converted to analog data by I Digital-to-Analog Converter (DAC)
14
a
and Q DAC
14
b
, respectively. The outputs of the respective DACs
14
a
and
14
b
are applied to the respective low pass filters
12
a
and
12
b
to provide the respective I and Q data inputs
11
a
and
11
b.
The modulator modulates the input data on a carrier
13
, by summing the outputs of the multipliers
16
a
,
16
b
at a summing node
218
. The modulated carrier is amplified by a power amplifier
22
and transmitted via an antenna
24
.
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 IQ modulation systems and methods that can provide high power modulation while reducing the amount of battery power that is consumed. Unfortunately, the power amplifier
22
of an IQ modulator may consume excessive power due to efficiency limitations therein. More specifically, it is known to provide a linear class-A or class-AB power amplifier
22
that may have efficiencies as low as 30 percent or less. Thus, large amounts of battery power may be wasted as heat. Moreover, the noise figure of a conventional IQ modulator may be excessive so that high cost Surface Acoustic Wave (SAW) filters may need to be used.
It is also known to separately modulate the amplitude and phase of an input signal using an “rTheta” technique. In the rTheta technique, the phase is modulated at the oscillator, and the amplitude is modulated at the power amplifier stage. Unfortunately, the rTheta technique may require the oscillator phase lock loop to support the phase modulation bandwidth. With wide bandwidth radiotelephone signals such as TDMA and CDMA signals, it may be increasingly difficult to provide the requisite bandwidth in the oscillator phase lock loop.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide improved IQ modulation systems and methods.
It is another object of the present invention to provide IQ modulation systems and methods that can provide high efficiency.
It is still another object of the present invention to provide IQ modulation systems and methods that do not require the use of linear amplifiers.
These and other objects are provided, according to the present invention, by providing power IQ modulation systems that modulate in-phase (I) and quadrature-phase (Q) input signals in the power amplifiers themselves. High efficiency class-C and class-D power amplifiers may be used.
Power modulation systems according to the present invention include first and second power amplifiers, each including a signal input, a supply voltage input and a power output. The first and second power amplifiers are preferably class-C power amplifiers. A source of first, second, third and fourth reference frequency signals is also provided. The first and second reference frequency signals are inverted relative to one another, and the third and fourth reference frequency signals are inverted relative to one another. Preferably, the first, second, third and fourth reference frequency signals are 0°, 180°, 90° and 270° phase shifted reference frequency signals, respectively.
A switching system is also provided that selectively applies one of the first and second reference frequency signals to the signal input of the first power amplifier as a function of the polarity of one of the I and Q input signals. The switching system also selectively applies one of the third and fourth reference frequency signals to the signal input of the second power amplifier as a function of the polarity of the other of the I and Q input signals.
A third amplifier, preferably a class-D amplifier, is responsive to the one of the I and Q input signals to supply a first variable supply voltage to the supply input of the first amplifier. The supply voltage input preferably corresponds to the drain or collector voltage of the output stage of the first amplifier. A fourth amplifier, also preferably a class-D amplifier, is responsive to the other of I and Q input signals to supply a second variable supply voltage to the supply input of the second amplifier. A coupler couples the power outputs of the first and second power amplifiers to a load such as a radiotelephone antenna. Accordingly, power IQ modulation is provided that can use class-C and class-D amplifiers that are highly efficient.
The first, second, third and fourth reference frequency signals may be generated by a controlled oscillator that produces the first reference frequency signal. A first inverter is responsive to the controlled oscillator to produce the second reference frequency signal. A phase shifter is responsive to the controlled oscillator to produce the third reference frequency signal. A second inverter is responsive to the phase shifter to produce the fourth reference frequency signal.
The switching system may include a first switch that is responsive to the one of the I and Q input signals being positive, to couple the first reference frequency signal to the first power amplifier. The first switch is also responsive to the one of the I and Q input signals being negative, to couple the second reference frequency signal to the first power amplifier. A second switch is responsive to the other of the I and Q input signals being positive, to couple the third reference frequency signal to the second power amplifier. The second switch is also responsive to the other of the I and Q input signals being negative to couple the fourth reference frequency signal to the second power amplifier. A first polarity detector may be provided, that is coupled between the one of the I and Q input signals and the first switch, to detect whether the one of the I and Q input signals is positive or negative. A second polarity detector may also be provided, that is coupled between the other of I and Q input signals and the second switch, to detect whether the other of the I and Q input signals is positive or negative.
A first analog-to-digital converter also may be coupled between the one of the I and Q input signals and the third amplifier, such that the third amplifier is responsive to a digital representation of the one of the I and Q signals to supply a first variable supply voltage to the supply input of the first amplifier. A second analog-to-digital converter also may be provided, that is coupled between the other of the I and Q input signals and the fourth amplifier, such that the fourth amplifier is responsive to a digital representation of the other of the I and Q signals to supply a second variable voltage supply to the supply input of the second amplifier. The analog-to-digital converters are preferably delta-sigma analog-to-digital converters.
Various embodiments of couplers that couple the power outputs of the
Camp, Jr. William O.
Dent Paul W.
Holden Alan R.
Ericsson Inc.
Myers Bigel & Sibley & Sajovec
Nguyen Khanh Van
Pascal Robert
LandOfFree
Power IQ modulation systems and methods does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power IQ modulation systems and methods, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power IQ modulation systems and methods will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2522940