Dual-band signal transmission
A method and system for modulating a drain supply voltage of a power amplifier are disclosed. A low pass envelope of a dual band modulated signal input to the power amplification system is determined. The determined low pass envelope is amplified. A drain supply of the power amplifier is modulated based on the amplified determined low pass envelope.
1. A method of envelope tracking modulation of a power amplifier in a power amplification system, the method comprising:
determining a low pass envelope of a dual band modulated signal to the power amplification system, wherein the dual band modulated signal, ν DB (t), is of the form:
v
DB
(
t
)
=
v
1
(
t
)
+
v
2
(
t
)
=
I
1
(
t
)
cos
(
ω
c
1
t
)
+
Q
1
(
t
)
sin
(
ω
c
1
t
)
+
I
2
(
t
)
cos
(
ω
c
2
t
+
θ
0
)
+
Q
2
(
t
)
sin
(
ω
c
2
t
+
θ
0
)
;
where ω c1 is a carrier frequency of first signal, ν 1 , of the dual band modulated signal, ω c2 is a carrier frequency of second signal, ν 2 , of the dual band modulated signal, θ 0 is a phase offset, I and Q are in-phase and quadrature components of a signal ν, and wherein the low pass envelope is given by:
α LF ( t )=(√{square root over ( I 1 2 ( t )+ Q 1 2 ( t ))}+√{square root over ( I 2 2 ( t )+ Q 2 2 ( t ))});
amplifying the determined low pass envelope; and
modulating a drain supply of the power amplifier based on the amplified determined low pass envelope.
2. The method of claim 1 , wherein the low pass envelope is an envelope of an envelope of the dual band modulated signal.
3. The method of claim 1 , wherein a bandwidth of the low pass envelope is about equal to a largest bandwidth of the first signal, ν 1 , and the second signal, ν 2 , comprising the dual band modulated signal.
4. The method of claim 1 , wherein the determined low pass envelope is shaped according to a polynomial function of the determined low pass envelope prior to the amplifying.
5. The method of claim 1 , further comprising pre-distorting the dual band modulated signal according to a dual band baseband equivalent Volterra model extended to compensate for distortion attributable to the drain supply modulation.
6. The method of claim 5 , wherein the dual band baseband equivalent Volterra model extended to compensate for distortion attributable to the drain supply modulation is of the form:
y
~
i
(
n
)
=
f
i
(
x
~
1
,
x
~
2
)
×
∑
l
=
0
N
s
-
1
c
l
(
i
)
(
x
~
1
(
n
)
+
x
~
2
(
n
)
)
l
where f i is a dual band describing function without drain supply modulation for band i, Ns is a nonlinearity order for an effect of the drain supply modulation, c i are model coefficients for band i, and wherein {tilde over (x)} 1 and {tilde over (x)} 2 are baseband equivalent envelopes of the first signal, ν 1 , and the second signal, ν 2 , comprising the dual-band modulated signal.
7. The method of claim 6 , wherein the model coefficients for band i, i.e., c i , are identified linearly using a least square error estimator.
8. A power amplification system using envelope tracking for a power amplifier, the power amplifier having an input, an output and a drain supply, the power amplification system comprising:
a low pass envelope detector configured:
to determine a low pass envelope of a multi-band modulated signal to the power amplification system, wherein the multi band modulated signal is a dual band modulated signal, ν DB (t), of the form:
v
DB
(
t
)
=
v
1
(
t
)
+
v
2
(
t
)
=
I
1
(
t
)
cos
(
ω
c
1
t
)
+
Q
1
(
t
)
sin
(
ω
c
1
t
)
+
I
2
(
t
)
cos
(
ω
c
2
t
+
θ
0
)
+
Q
2
(
t
)
sin
(
ω
c
2
t
+
θ
0
)
;
where ω c1 is a carrier frequency of first signal, ν 1 , of the dual band modulated signal, ω c2 is a carrier frequency of second signal, ν 2 , of the dual band modulated signal, θ 0 is a phase offset, I and Q are in-phase and quadrature components of a signal ν and wherein the low pass envelope is given by:
α LF ( t )=(√{square root over ( I 1 2 ( t )+ Q 1 2 ( t ))}+√{square root over ( I 2 2 ( t )+ Q 2 2 ( t ))}), and
to output the determined low pass envelope; and
an envelope amplifier configured to modulate the drain supply of the power amplifier according to the determined low pass envelope received from the envelope detector.
9. The power amplification system of claim 8 , wherein the low pass envelope detector is configured to detect an envelope of an envelope of the multi-band modulated signal.
10. The power amplification system of claim 8 , wherein a bandwidth of the low pass envelope is about equal to a largest bandwidth of the first signal, ν 1 , and the second signal, ν 2 , individual signals comprising the multi-band modulated signal.
11. The power amplification system of claim 8 , further comprising an envelope shaper configured to receive and shape the determined low pass envelope according to a polynomial function of the determined low pass envelope, and to output the shaped determined low pass envelope to the envelope amplifier.
12. The power amplification system of claim 8 , further comprising a pre-distorter configured to pre-distort the dual band modulated signal according to a multi-band baseband equivalent Volterra model extended to compensate for distortion attributable to the drain supply modulation.
13. The power amplification system of claim 12 , wherein the multi-band baseband equivalent Volterra model extended to compensate for distortion attributable to the drain supply modulation is a dual band model of the form:
y
~
i
(
n
)
=
f
i
(
x
~
1
,
x
~
2
)
×
∑
l
=
0
N
s
-
1
c
l
(
i
)
(
x
~
1
(
n
)
+
x
~
2
(
n
)
)
l
where f i is a dual band describing function without drain supply modulation for band i, Ns is a nonlinearity order for an effect of the drain supply modulation, c i are model coefficients for band i, and wherein {tilde over (x)} 1 and {tilde over (x)} 2 are baseband equivalent envelopes of the first signal, ν 1 , and the second signal, ν 2 comprising the multi-band modulated signal.
14. The power amplification system of claim 13 , further comprising a least square estimator configured to linearly identify the model coefficients for band i, i.e., c i .
15. A power amplification system using envelope tracking, the power amplification system comprising:
a low pass envelope detector configured to determine a low pass envelope of a multi-band modulated signal to the power amplification system and to output the determined low pass envelope;
an envelope amplifier configured to receive and amplify the determined low pass envelope to produce an envelope amplifier output;
a power amplifier having a drain supply that is modulated by the envelope amplifier output received from the envelope amplifier; and
a pre-distorter configured to pre-distort the multi-band modulated signal according to a multi-band baseband equivalent Volterra model extended to compensate for distortion attributable to the drain supply modulation, wherein the multi-band baseband equivalent Volterra model is extended by multiplication by a function of the low pass envelope.
16. The power amplification system of claim 15 , wherein a bandwidth of the low pass envelope is about equal to a largest bandwidth of individual signals comprising the multi-band modulated signal.