Modulation agnostic digital hybrid mode power amplifier system and method
A RF-digital hybrid mode power amplifier system for achieving high efficiency and high linearity in wideband communication systems is disclosed. The present invention is based on the method of adaptive digital predistortion to linearize a power amplifier in the RF domain. The present disclosure enables a power amplifier system to be field reconfigurable and support multi-modulation schemes (modulation agnostic), multi-carriers and multi-channels. As a result, the digital hybrid mode power amplifier system is particularly suitable for wireless transmission systems, such as base-stations, repeaters, and indoor signal coverage systems, where baseband I-Q signal information is not readily available.
1. A digital predistortion system for linearizing the output of power amplifiers comprising:
input signal suitable for wireless communications;
at least one power amplifier for outputting an amplified signal;
at least one feedback signal derived from the amplified signal including a representation of a noise characteristic of the at least one power amplifier;
estimator logic responsive to the at least one feedback signal for generating predistortion coefficients a ij , based at least in part on feedback path delay determined from the correlation given by the equation
c
(
m
)
=
∑
i
=
0
N
-
1
sign
(
x
(
i
+
1
)
-
x
(
i
)
)
sign
(
y
(
i
+
m
+
1
)
-
y
(
i
+
m
)
)
where C(m) is a correlation function, x(n) represents transmission data, y(n) represents feedback data, c(m) is a correlation function, N is a number of data per block, m is a variable representing time, i is a counter for summation, and n(delay) is a delay determined by the value of m where C(m) is maximized; and
digital predistortion logic for predistorting the input signal and for supplying a predistorted signal to the at least one power amplifier, wherein the digital predistortion logic complies with the equation:
z
(
n
)
=
∑
i
=
0
n
-
1
x
t
(
n
-
i
)
(
∑
j
=
0
k
-
1
a
ij
x
t
(
n
-
i
)
j
)
where z(n) is a predistortion function, n is a variable representing time, x t is the input signal, i and j are counters for summation, and a ij are the predistortion coefficients determined by the estimator logic.
2. The digital predistortion system of claim 1 configured for base station applications further comprising a digital field programmable gate array that includes one or more of a digital up-converter, a crest factor reduction, a predistorter, or a digital quadrature modulator.
3. The digital predistortion system of claim 1 configured for repeater applications further comprising a digital field programmable gate array that includes at least one of a digital quadrature demodulator, a crest factor reduction, a predistorter, or a digital quadrature modulator.
4. The digital predistortion system of claim 1 further comprising a digital field programmable gate array that provides predistortion that compensates adaptively for both nonlinearity and memory effects by generating asymmetric distortion of the power amplifier.
5. The digital predistortion system of claim 1 further comprising a digital field programmable gate array that includes an adaptation algorithm to determine the optimum gate bias voltage of the power amplifier for stabilizing the linearity fluctuations due to the temperature changes of the power amplifier.
6. The digital predistortion system of claim 1 wherein the at least one power amplifier uses at least one of the following efficiency boosting techniques: Doherty, Envelope Elimination and Restoration, Envelope Tracking, Envelope Following, or Linear amplification using Nonlinear Components in order to maximize the efficiency of the power amplifier system.
7. A digital predistortion method for linearizing the output of power amplifiers comprising:
receiving an input signal suitable for wireless communications,
amplifying the input signal using at least one power amplifier,
deriving at least one feedback signal from the amplified signal including a representation of a noise characteristic of the at least one power amplifier,
generating predistortion coefficients a ij , using estimator logic responsive to the at least one feedback signal based at least in part on feedback path delay determined from the correlation given by the equation
c
(
m
)
=
∑
i
=
0
N
-
1
sign
(
x
(
i
+
1
)
-
x
(
i
)
)
sign
(
y
(
i
+
m
+
1
)
-
y
(
i
+
m
)
)
where C(m) is a correlation function, x(n) represents transmission data, y(n) represents feedback data, c(m) is a correlation function, N is a number of data per block, m is a variable representing time, I is a counter for summation, and n(delay) is a delay determined by the value of m where C(m) is maximized; and
predistorting the input signal and supplying a predistorted signal to the at least one power amplifier, wherein the predistorting complies with the equation:
z
(
n
)
=
∑
i
=
0
n
-
1
x
t
(
n
-
i
)
(
∑
j
=
0
k
-
1
a
ij
x
t
(
n
-
i
)
j
)
where z(n) is a predistortion function, n is a variable representing time, x t is the input signal, i and j are counters for summation, and a ij are the predistortion coefficients determined by the estimator logic.
8. The digital predistortion method of claim 7 further comprising providing predistortion that compensates adaptively for both nonlinearity and memory effects by generating asymmetric distortion of the power amplifier using a digital field programmable gate array.
9. The digital predistortion method of claim 7 further comprising determining the optimum gate bias voltage of the power amplifier for stabilizing the linearity fluctuations due to the temperature changes of the power amplifier using an adaptation algorithm of a digital field programmable gate array.
10. The digital predistortion method of claim 7 wherein the at least one power amplifier uses at least one of the following efficiency boosting techniques: Doherty, Envelope Elimination and Restoration, Envelope Tracking, Envelope Following, or Linear amplification using Nonlinear Components in order to maximize the efficiency of the power amplifier system.
11. The digital predistortion method of claim 7 configured for base station applications further comprising digitally upconverting the input signal, reducing crest factor of the input signal, predistorting the input signal, or modulating the input signal.
12. The digital predistortion method of claim 7 configured for repeater applications further comprising demodulating the input signal, reducing crest factor of the input signal, predistorting the input signal, or modulating the input signal.