Wideband and reconfigurable Doherty based amplifier
The present disclosure provides a power amplifier comprising a main amplifier and an auxiliary amplifier. The power amplifier is configured to deliver an output power P out . A First Efficiency Peak (FEP) is defined as a first efficiency peak in the power ratio P out to P outmax . P outmax is a maximum power output of the power amplifier and P FEP defines a power ratio at the FEP. The main amplifier is configured to be biased by a main amplifier bias V ds,m that is substantially equal to an auxiliary amplifier bias V ds,a times x b with x b being a main amplifier output current in relation to the maximum current through the main amplifier when P out equals P FEP . The impedances of a load and a main amplifier transmission line are arranged to be substantially equal. A corresponding method and a node in a wireless communication system comprising the power amplifier are also disclosed.
1. A power amplifier comprising:
a main amplifier connected at an output end to a load, wherein the main amplifier is connected to the load via a main amplifier transmission line having an input impedance and a characteristic impedance, and wherein the main amplifier is configured to:
receive an input signal;
generate a main amplifier output current; and
operate with a drain-source or collector-emitter bias V ds,m ; and
an auxiliary amplifier connected at an output end to the load, and configured to:
receive an input signal;
generate an auxiliary amplifier output current; and
operate with a drain-source or collector-emitter bias V ds,c ;
wherein each of the main amplifier and auxiliary amplifier are configured to operate over a bandwidth having a center frequency;
wherein the power amplifier is configured to deliver an output power P out ;
wherein the auxiliary amplifier output current is configured to be set to zero below a First Efficiency Peak (FEP), the FEP being a first efficiency peak in the power ratio P out to P outmax , P outmax being a maximum power output of the power amplifier and P FEP defining a power ratio at the FEP;
wherein the main amplifier is further configured to be biased by V ds,m being substantially equal to V ds,a times x b , x b being a main amplifier output current in relation to a maximum current through the main amplifier, I max,m , when P OUT =P FEP ; and
wherein the impedance of the load and the impedance of the main amplifier transmission line are both arranged to be substantially equal to V ds,a divided by I max,m , making the input impedance to the main amplifier transmission line independent of frequency below P FEP , and also making the efficiency of the power amplifier independent of frequency below P FEP .
2. The power amplifier of claim 1 , wherein the power amplifier has a single RF-input that is split into a first single input signal for the main amplifier and a second single input signal for the auxiliary amplifier.
3. The power amplifier of claim 2 , wherein the main amplifier is configured to be biased as a class AB or class B amplifier, and the auxiliary amplifier is configured to be biased as a class C or B amplifier.
4. The power amplifier of claim 1 , wherein the power amplifier has a dual RF-input comprising:
a first input configured to provide a first dual input signal as the input signal of the main amplifier; and
a second input configured to provide a second dual input signal as the input signal of the auxiliary amplifier;
wherein the first and second dual input signals constitute an RF-input signal to the power amplifier.
5. The power amplifier of claim 4 , wherein both the main and the auxiliary amplifier are configured to be biased as class B amplifiers.
6. The power amplifier of claim 1 , wherein the main amplifier transmission line has an electrical length of substantially a quarter of a wavelength at the center frequency.
7. The power amplifier of claim 1 , wherein a relation between the main amplifier output current and the auxiliary amplifier output current is arranged to be frequency dependent above P FEP , thus minimizing the frequency dependency of the efficiency above P FEP .
8. The power amplifier of claim 7 , wherein a frequency and amplitude dependency between the main and auxiliary amplifier output currents above the FEP is arranged substantially as follows:
I
a
=
2
kI
max
,
m
(
I
m
_
-
x
b
)
ⅇ
ⅈθ
,
x
b
<
I
m
_
≤
1
θ
=
arccos
(
-
k
(
I
m
_
-
x
b
)
cos
(
Φ
f
0
f
_
)
I
m
_
)
,
x
b
<
I
m
_
≤
1
k
=
(
I
m
2
_
+
x
b
2
)
4
(
I
m
_
-
x
b
)
2
-
1
4
(
I
m
_
-
x
b
)
(
I
m
2
_
+
x
b
2
I
m
_
-
x
b
)
2
-
(
I
m
_
+
x
b
sin
(
Φ
f
0
f
_
)
)
2
where I max,m is a maximum current through the main amplifier, I a is an amplitude of the auxiliary amplifier output current, θ is a phase difference between the auxiliary amplifier output current and the main amplifier output current, f is a normalized frequency defined as the frequency divided by the center frequency, and Φ fc is an electrical length of the main amplifier transmission line expressed in degrees or radians at the center frequency, Φ fc being arranged to be substantially equal to 90 degrees above the FEP.
9. The power amplifier of claim 1 :
wherein x b is equal to 1U P FEP /20 ; and
wherein P FEP and x b are arranged to be reconfigured, as the load impedance is independent of frequency and x b without affecting hardware by changing the drain-source or collector-emitter bias V ds,m and the auxiliary amplifier output current.
10. The power amplifier of claim 1 , wherein the power amplifier is included in a node in a wireless communication system.
11. A method of operating a power amplifier to deliver an output power P out , the power amplifier including a main amplifier and an auxiliary amplifier each receiving an input signal, operating in parallel, being connected to a load at an output end, and operating over a bandwidth B having a center frequency, the method comprising:
generating a main amplifier output current from the main amplifier, the main amplifier being connected to the load via a main amplifier transmission line having an input impedance and a characteristic impedance;
operating the main amplifier with a drain-source or collector-emitter bias V ds,m ;
biasing the main amplifier by setting V ds,m substantially equal to V ds,s times x b , x b being a main amplifier output current in relation to a maximum current through the main amplifier, I max,m , when P out =P FEP ;
generating an auxiliary amplifier output current from the auxiliary amplifier;
operating the auxiliary amplifier with a drain-source or collector-emitter bias V ds,a ;
biasing the auxiliary amplifier by adjusting V ds,a for operation with one or more selected transistors in the auxiliary amplifier;
setting the auxiliary amplifier output current to zero below a First Efficiency Peak (FEP), thus making the efficiency independent of frequency below P FEP ; and
selecting the impedances of the load and the main amplifier transmission line both to be substantially equal to V ds,a divided by I max,m , making the input impedance to the main amplifier transmission line independent of frequency below P FEP ;
wherein the FEP is defined as a first efficiency peak in the power ratio P out to P outmax ;
wherein P outmax is a maximum power output of the power amplifier; and
wherein P FEP is a power ratio at the FEP.
12. The method of claim 11 , wherein the main amplifier transmission line has an electrical length of substantially a quarter of a wavelength at the center frequency.
13. The method of claim 11 , further comprising:
optimizing currents above the FEP by selecting the main amplifier output current and the auxiliary amplifier output current to be frequency dependent above P FEP , thus minimizing the frequency dependency of the efficiency above P FEP .
14. The method of claim 13 , further comprising:
optimizing currents above the FEP by configuring a frequency and amplitude dependency between the main and auxiliary amplifier output currents substantially as follows:
I
a
=
2
kI
max
,
m
(
I
m
_
-
x
b
)
ⅇ
ⅈθ
,
x
b
<
I
m
_
≤
1
θ
=
arccos
(
-
k
(
I
m
_
-
x
b
)
cos
(
Φ
f
0
f
_
)
I
m
_
)
,
x
b
<
I
m
_
≤
1
k
=
(
I
m
2
_
+
x
b
2
)
4
(
I
m
_
-
x
b
)
2
-
1
4
(
I
m
_
-
x
b
)
(
I
m
2
_
+
x
b
2
I
m
_
-
x
b
)
2
-
(
I
m
_
+
x
b
sin
(
Φ
f
0
f
_
)
)
2
where I max/m is a maximum current through the main amplifier, I a is an amplitude of the auxiliary amplifier output current, θ is a phase difference between the auxiliary amplifier output current and the main amplifier output current, f is a normalized frequency defined as the frequency divided by the center frequency, and Φ fc is an electrical length of the main amplifier transmission line expressed in degrees or radians at the center frequency, Φ fc being adjusted to be substantially equal to 90 degrees above the FEP.
15. The method of claim 11 , further comprising:
reconfiguring P FEP and x b , as the load impedance is independent of frequency and x b without affecting hardware by changing the drain-source or collector-emitter bias V ds,m and the auxiliary amplifier output current;
wherein x b is equal to 10 P FEP /20 .