Calibrating amplitude and phase imbalance and DC offset of an analog I/Q modulator in a high-frequency transmitter
View Patent ↗The object of the invention, which relates to a method and an arrangement for calibrating an analog I/Q modulator in a high-frequency transmitter, is to provide a method and an associated circuit arrangement by means of which a calibration of the I/Q modulator is carried out without a balancing operation and thus the complexity is minimized. According to the invention, this object is achieved, in terms of the method, in that transmission signals are produced by the I/Q modulator in three method steps in accordance with the method and said transmission signals are in each case evaluated and the results of the evaluations are stored, in that, in a fourth method step, improved compensation coefficients are calculated on the basis of the results of the previous evaluations, which improved compensation coefficients can be used for a subsequent run-through of the method, and in that the run-throughs of the method are repeated until the error of the amplitude and/or phase response of the I/Q modulator lies below a defined threshold value or a defined number of run-throughs of the method is reached.
1. A method of calibrating an analog I/Q modulator in a high-frequency transmitter, in which an input signal is weighted in an in-phase path and in a quadrature phase path by respectively a first and a second compensation coefficient prior to the I/Q modulation, and an output signal is produced, comprising:
in a first method step, providing the high-frequency transmitter
in a second method step, the first compensation coefficients C I , C Q ( 3 ), which affect the sideband suppression of the output signal, and the second compensation coefficients D I , D Q ( 3 ), which affect the carrier suppression of the output signal ( 12 ), are in each case set to a first predefined value C I,1 , C Q,1 , D I,1 and D Q,1 , in that the input of the I/Q modulator ( 1 ) is supplied with an input signal which satisfies a rotating exponential function with the frequency f 0 , a first I/Q modulator output signal ( 12 ) is produced and fed to a first evaluation and the result of the first evaluation is stored, in that,
in a third method step, the first and second compensation coefficients ( 3 ) are in each case set to a second defined value C I,2, D I,2 and D Q,2 and a second I/Q modulator output signal ( 12 ) is produced, fed to a second evaluation and the result of the second evaluation is stored, in that,
in a fourth method step, the first and second compensation coefficients ( 3 ) are in each case set to a third defined value C I,3, D I,3 and D Q,3 and a third I/Q modulator output signal ( 12 ) is produced, fed to a third evaluation and the result of the third evaluation is stored, in that,
in a fifth method step, improved compensation coefficients ( 3 ) which reduce at least one of an amplitude, a phase imbalance of the I/Q modulator ( 1 ) and an amplitude of the residual carrier are calculated for the first and second compensation coefficients ( 3 ) from the results stored in the second, third and fourth method steps, and
wherein the second, third, fourth and fifth method steps are repeated using these improved compensation coefficients ( 3 ) until at least one of the error of the amplitude and a phase response of the I/Q modulator ( 1 ) lies below a defined threshold value or a defined number of run-throughs of the method is reached.
2. A method as claimed in claim 1 , characterized in that the first compensation coefficients ( 3 ) C I , C Q or the second compensation coefficients ( 3 ) D I , D Q have the same value for the second, third and fourth method step.
3. A method as claimed in claim 1 , characterized in that, for the second method step, at least one of the first compensation coefficients ( 3 ) C I , C Q and the second compensation coefficients ( 3 ) D I , D Q are set to compensation coefficients ( 3 ) determined in a previous run-through of the method.
4. A method as claimed in claim 1 , characterized in that at least one of the compensation coefficients ( 3 ) C I , C Q , D I , D Q is acted upon by at least one of a change value AC and AD prior to a subsequent method step.
5. A method as claimed in claim 1 , characterized in that the input signal fed in at the input of the I/Q modulator ( 1 ), which satisfies a rotating exponential function with the frequency f 0 , is produced from a partial function S I (t)=A 0 *cos(2πf 0 t+φ 0 ) for the in-phase input and a partial function s Q (t)=A 0 *sin(2πf 0 +φ 0 ) for the quadrature phase input.
6. A method as claimed in claim 1 , characterized in that the I/Q modulator output signal ( 12 ) is subjected to power detection and thus a level indicator output signal p(t) is produced, in that the first evaluation takes place in accordance with
v
I
,
1
:=
∫
0
NT
0
p
1
(
t
)
·
w
I
(
t
)
·
ⅆ
t
and
v
Q
,
1
:=
∫
0
NT
0
p
1
(
t
)
·
w
Q
(
t
)
·
ⅆ
t
,
wherein, in order to determine improved first compensation coefficients ( 3 ) C I and C Q , w I , (t)=cos(4πf 0 t) and w Q (t)=sin(4πf 0 t), in that the second evaluation takes place in accordance with
v
I
,
2
:=
∫
0
NT
0
p
2
(
t
)
·
w
I
(
t
)
·
ⅆ
t
and
v
Q
,
2
:=
∫
0
NT
0
p
2
(
t
)
·
w
Q
(
t
)
·
ⅆ
t
,
in that the third evaluation takes place in accordance with
v
I
,
3
:=
∫
0
NT
0
p
3
(
t
)
·
w
I
(
t
)
·
ⅆ
t
and
v
Q
,
3
:=
∫
0
NT
0
p
3
(
t
)
·
w
Q
(
t
)
·
ⅆ
t
,
in that the determination of the improved first compensation coefficients ( 3 ) C I and C Q is carried out in accordance with z 1 :=v Q,3 v I,2 −v I,3 v Q,2 , z 2 :=v I,3 v Q,1 −v Q,3 v I,1 , z 3 :=v Q,2 v I,1 −v I,2 v Q,1 and R:=1/(z 1 +z 2 +z 3 ) and also C I =(C I,1 ·z 1 +C I,2 ·z 2 +C I,3 ·z 3 )·R and C Q =(C Q,1 ·z 1 +C Q,2 ·z 2 +C Q,3 ·z 3 )·R or the determination of the improved second compensation coefficients ( 3 ) D I and D Q , wherein w I (t)=cos(2πf 0 t) and w Q (t)=sin(2πf 0 t), is carried out in accordance with z 1 :=v Q,3 v I,2 −v I,3 v Q,2 , z 2 :=v I,3 v Q,1 −v Q,3 v I,1 , z 3 :=v Q,2 v I,1 −v I,2 v Q,1 and R:=1/(z 1 +z 2 +z 3 ) and also D I =(D I,1 ·z 1 +D I,2 ·z 2 +D I,3 ·z 3 )·R and D Q =(D Q,1 ·z 1 +D Q,2 ·z 2 +D Q,3 ·z 3 )·R.
7. A method as claimed in claim 1 , characterized in that the I/Q modulator output signal ( 12 ) is subjected to an I/Q demodulation and thus a complex baseband received signal r(t)=r I (t)+r Q (t) is produced, in that the first evaluation takes place in accordance with
v
I
,
1
:=
∫
0
NT
0
r
I
,
1
(
t
)
·
ⅆ
t
and
v
Q
,
1
:=
∫
0
NT
0
r
Q
,
1
(
t
)
·
ⅆ
t
,
in that the second evaluation takes place in accordance with
v
I
,
2
:=
∫
0
NT
0
r
I
,
2
(
t
)
·
ⅆ
t
and
v
Q
,
2
:=
∫
0
NT
0
r
Q
,
2
(
t
)
·
ⅆ
t
,
in that the third evaluation takes place in accordance with
v
I
,
3
:=
∫
0
NT
0
r
I
,
3
(
t
)
·
ⅆ
t
and
v
Q
,
3
:=
∫
0
NT
0
r
Q
,
3
(
t
)
·
ⅆ
t
,
in that the determination of the improved second compensation coefficients ( 3 ) D I and D Q is carried out in accordance with z 1 :=v Q,3 v I,2 −v I,3 v Q,2 , z 2 :=v I,3 v Q,1 −v Q,3 v I,1 , z 3 :=v Q,2 v I,1 −v I,2 v Q,1 and R:=1/(z 1 +z 2 +z 3 ) and also D I =(D I,1 ·z 1 +D I,2 ·z 2 +D I,3 ·z 3 )·R and D Q =(D Q,1 ·z 1 +D Q,2 ·z 2 +D Q,3 ·z 3 )·R or the first evaluation takes place in accordance with
v
I
,
1
:=
∫
0
NT
0
r
I
,
1
(
t
)
·
w
I
(
t
)
+
r
Q
1
(
t
)
·
w
Q
(
t
)
·
ⅆ
t
and
v
Q
,
1
:=
∫
0
NT
0
r
Q
,
1
(
t
)
·
w
I
(
t
)
-
r
I
1
(
t
)
·
w
Q
(
t
)
·
ⅆ
t
,
in that the second evaluation takes place in accordance with
v
I
,
2
:=
∫
0
NT
0
r
I
,
2
(
t
)
·
w
I
(
t
)
+
r
Q
2
(
t
)
·
w
Q
(
t
)
·
ⅆ
t
and
v
Q
,
2
:=
∫
0
NT
0
r
Q
,
2
(
t
)
·
w
I
(
t
)
-
r
I
2
(
t
)
·
w
Q
(
t
)
·
ⅆ
t
,
in that the third evaluation takes place in accordance with
v
I
,
3
:=
∫
0
NT
0
r
I
,
3
(
t
)
·
w
I
(
t
)
+
r
Q
3
(
t
)
·
w
Q
(
t
)
·
ⅆ
t
and
v
Q
,
3
:=
∫
0
NT
0
r
Q
,
3
(
t
)
·
w
I
(
t
)
-
r
I
3
(
t
)
·
w
Q
(
t
)
·
ⅆ
t
,
in that the determination of the improved first compensation coefficients ( 3 ) C I and C Q is carried out in accordance with z 1 :=v Q,3 v I,2 −v I,3 v Q,2 , z 2 :=v I,3 v Q,1 −v Q,3 v I,1 , z 3 :=v Q,2 v I,1 −v I,2 v Q,1 and R:=1/(z 1 +z 2 +z 3 ) and also C I =(C I,1 ·z 1 +C I,2 ·z 2 +C I,3 ·z 3 )·R and C Q =(C Q,1 ·z 1 +C Q,2 ·z 2 +C Q,3 ·z 3 )·R.
8. A method as claimed in either of claims 6 and 7 , characterized in that the integrations used in the method take place in a time-discrete manner such that sampling of the function variation takes place with a subsequent summation.
9. A method as claimed in claim 1 , characterized in that the method takes place during start-up of the high-frequency transmitter, in a time-controlled manner, in the event of changing ambient conditions such as at least one of pressure and temperature and in an event of a change in operating mode of the high-frequency transmitter.