Signal correction techniques
View Patent ↗Errors present in the output of an amplifier ( 10 ) are compared with the amplifier input in a control unit ( 24 ) to derive corrected coefficients for a look-up table used by predistorter ( 12 ) to eliminate distortion in the output of the amplifier ( 10 ). Depending on the format of the predistorter ( 12 ), at least some of the coefficients are corrected using measured errors that have been rendered independent of the input signal's amplitude.
1. A method for updating a first look-up table (LUT) used by distortion counteracting equipment to counteract distortion in signal handling equipment, the method comprising:
generating an error signal between (1) an output signal generated by the signal handling equipment based on an input signal having an amplitude and (2) a desired output signal for the signal handling equipment;
generating a ratio by dividing the error signal by the amplitude of the input signal; and
updating the first LUT based on the ratio of the error signal to the amplitude of the input signal.
2. The invention of claim 1 , wherein:
the distortion counteracting equipment uses the first LUT to counteract amplitude distortion in the signal handling equipment; and
the first LUT is updated based on a ratio of amplitude of the error signal to the amplitude of the input signal.
3. The invention of claim 2 , wherein:
the distortion counteracting equipment uses a second LUT to counteract phase distortion in the signal handling equipment; and
the second LUT is updated based on phase of the error signal independent of the amplitude of the input signal.
4. The invention of claim 1 , wherein:
the distortion counteracting equipment uses the first LUT to counteract in-phase distortion in the signal handling equipment; and
the first LUT is updated based on a ratio of an in-phase component of the error signal to the amplitude of the input signal.
5. The invention of claim 4 , wherein:
the distortion counteracting equipment uses a second LUT to counteract quadrature distortion in the signal handling equipment; and
the second LUT is updated based on a ratio of a quadrature component of the error signal to the amplitude of the input signal.
6. The invention of claim 1 , wherein:
the distortion counteracting equipment uses the first LUT to counteract quadrature distortion in the signal handling equipment; and
the first LUT is updated based on a ratio of a quadrature component of the error signal to the amplitude of the input signal.
7. The invention of claim 1 , wherein:
a plurality of error signals are generated over time;
a plurality of average error signals are generated for different amplitudes of the input signal; and
the first LUT is updated based on a plurality of ratios, each ratio being a ratio of one of the plurality of average error signals to the corresponding amplitude of the input signal.
8. The invention of claim 7 , wherein the updating of the first LUT is further based on a loop gain parameter that is a function of the plurality of average error signals and is independent of the amplitude of the input signal.
9. The invention of claim 8 , wherein the distortion counteracting equipment updates the loop gain parameter based on magnitude of the function of the plurality of average error signals.
10. The invention of claim 8 , wherein the loop gain value is selected based on a sum of squares of the plurality of average error signals, such that the magnitude of the loop gain parameter is proportional to the magnitude of the sum of the squares of the plurality of average error signals.
11. The invention of claim 8 , wherein the first LUT is updated according to:
L
X
(
n
)
(
f
(
A
1
)
)
=
L
X
(
n
-
1
)
(
f
(
A
1
)
)
-
r
·
X
e
(
n
-
1
)
(
f
(
A
1
)
)
·
1
A
1
,
where:
A 1 is the amplitude of the input signal;
ƒ(A 1 ) is a specified function of the amplitude A 1 ;
L X(n−1) (ƒ(A 1 )) is the previous value stored in the first LUT for index ƒ(A 1 );
L X(n)(ƒ(A 1 )) is the updated value stored in the first LUT for index ƒ(A 1 );
r is the loop gain parameter; and
X e(n−1) (ƒ(A 1 )) is the average error signal corresponding to ƒ(A 1 )).
12. The invention of claim 11 , wherein:
the distortion counteracting equipment uses the first LUT to counteract amplitude distortion in the signal handling equipment; and
X e(n−1) (ƒ(A 1 )) is amplitude of the average error signal corresponding to ƒ(A 1 )).
13. The invention of claim 12 , wherein:
the distortion counteracting equipment uses a second LUT to counteract phase distortion in the signal handling equipment; and
the second LUT is updated according to:
L P (ƒ( A 1 )) =L P(n−1) (ƒ(A 1 ))− r·P e(n−1) (ƒ( A 1 )),
where:
L P(n−1) (ƒ(A 1 )) is the previous value stored in the second LUT for index ƒ(A 1 );
L P(n)(ƒ(A 1 )) is the updated value stored in the second LUT for index ƒ(A 1 ); and
P e(n−1) (ƒ(A 1 )) is phase of the average error signal corresponding to ƒ(A 1 )).
14. The invention of claim 11 , wherein:
the distortion counteracting equipment uses the first LUT to counteract in-phase distortion in the signal handling equipment; and
X e(n−1) (ƒ(A 1 )) is an in-phase component of the average error signal corresponding to ƒ(A 1 )).
15. The invention of claim 11 , wherein:
the distortion counteracting equipment uses the first LUT to counteract quadrature distortion in the signal handling equipment; and
X e(n−1) (ƒ(A 1 )) is a quadrature component of the average error signal corresponding to ƒ(A 1 )).
16. The invention of claim 1 , wherein:
the signal handling equipment is an amplifier; and
the distortion counteracting equipment is a predistorter that predistorts the input signals prior to being applied to the amplifier.
17. Distortion counteracting equipment for linearizing signal handling equipment using a first LUT to counteract distortion in the signal handling equipment, the distortion counteracting equipment adapted to:
generate an error signal between (1) an output signal generated by the signal handling equipment based on an input signal having an amplitude and (2) a desired output signal for the signal handling equipment;
generate a ratio by dividing the error signal by the amplitude of the input signal; and
update the first LUT based on the ratio of the error signal to the amplitude of the input signal.
18. The invention of claim 17 , wherein:
the signal handling equipment is an amplifier; and
the distortion counteracting equipment is a predistorter that predistorts the input signals prior to being applied to the amplifier.
19. A system comprising:
signal handling equipment adapted to generate an output signal based on an input signal having an amplitude; and
distortion counteracting equipment adapted to linearize the signal handling equipment using a first LUT to counteract distortion in the signal handling equipment, the distortion counteracting equipment adapted to:
generate an error signal between (1) the output signal generated by the signal handling equipment and (2) a desired output signal for the signal handling equipment;
generate a ratio by dividing the error signal by the amplitude of the input signal; and
update the first LUT based on the ratio of the error signal to the amplitude of the input signal.
20. The invention of claim 19 , wherein:
the signal handling equipment is an amplifier; and
the distortion counteracting equipment is a predistorter that predistorts the input signals prior to being applied to the amplifier.
21. A method for updating a first look-up table (LUT) used by distortion counteracting equipment to counteract distortion in signal handling equipment, the method comprising:
generating an error signal between (1) an output signal generated by the signal handling equipment based on an input signal having an amplitude and (2) a desired output signal for the signal handling equipment; and
updating the first LUT based on a ratio of the error signal to the amplitude of the input signal, wherein:
the distortion counteracting equipment uses the first LUT to counteract amplitude distortion in the signal handling equipment;
the first LUT is updated based on a ratio of amplitude of the error signal to the amplitude of the input signal;
the distortion counteracting equipment uses a second LUT to counteract phase distortion in the signal handling equipment; and
the second LUT is updated based on phase of the error signal independent of the amplitude of the input signal.
22. A method for updating a first look-up table (LUT) used by distortion counteracting equipment to counteract distortion in signal handling equipment, the method comprising:
generating an error signal between (1) an output signal generated by the signal handling equipment based on an input signal having an amplitude and (2) a desired output signal for the signal handling equipment; and
updating the first LUT based on a ratio of the error signal to the amplitude of the input signal, wherein:
the distortion counteracting equipment uses the first LUT to counteract in-phase distortion in the signal handling equipment; and
the first LUT is updated based on a ratio of an in-phase component of the error signal to the amplitude of the input signal.
23. The invention of claim 22 , wherein:
the distortion counteracting equipment uses a second LUT to counteract quadrature distortion in the signal handling equipment; and
the second LUT is updated based on a ratio of a quadrature component of the error signal to the amplitude of the input signal.
24. A method for updating a first look-up table (LUT) used by distortion counteracting equipment to counteract distortion in signal handling equipment, the method comprising:
generating an error signal between (1) an output signal generated by the signal handling equipment based on an input signal having an amplitude and (2) a desired output signal for the signal handling equipment; and
updating the first LUT based on a ratio of the error signal to the amplitude of the input signal, wherein:
the distortion counteracting equipment uses the first LUT to counteract quadrature distortion in the signal handling equipment; and
the first LUT is updated based on a ratio of a quadrature component of the error signal to the amplitude of the input signal.
25. A method for updating a first look-up table (LUT) used by distortion counteracting equipment to counteract distortion in signal handling equipment, the method comprising:
generating an error signal between (1) an output signal generated by the signal handling equipment based on an input signal having an amplitude and (2) a desired output signal for the signal handling equipment; and
updating the first LUT based on a ratio of the error signal to the amplitude of the input signal, wherein:
a plurality of error signals are generated over time;
a plurality of average error signals are generated for different amplitudes of the input signal; and
the first LUT is updated based on a plurality of ratios, each ratio being a ratio of one of the plurality of average error signals to the corresponding amplitude of the input signal.
26. The invention of claim 25 , wherein the updating of the first LUT is further based on a loop gain parameter that is a function of the plurality of average error signals and is independent of the amplitude of the input signal.
27. The invention of claim 26 , wherein the distortion counteracting equipment updates the loop gain parameter based on magnitude of the function of the plurality of average error signals.
28. The invention of claim 26 , wherein the loop gain value is selected based on a sum of squares of the plurality of average error signals, such that the magnitude of the loop gain parameter is proportional to the magnitude of the sum of the squares of the plurality of average error signals.
29. The invention of claim 26 , wherein the first LUT is updated according to:
L
X
(
n
)
(
f
(
A
1
)
)
=
L
X
(
n
-
1
)
(
f
(
A
1
)
)
-
r
·
X
e
(
n
-
1
)
(
f
(
A
1
)
)
·
1
A
1
,
where:
A 1 is the amplitude of the input signal;
ƒ(A 1 ) is a specified function of the amplitude A 1 ;
L X(n−1) (ƒ(A 1 )) is the previous value stored in the first LUT for index ƒ(A 1 );
L X(n)(ƒ(A 1 )) is the updated value stored in the first LUT for index ƒ(A 1 );
r is the loop gain parameter; and
X e(n−1) (ƒ(A 1 )) is the average error signal corresponding to ƒ(A 1 )).
30. The invention of claim 29 , wherein:
the distortion counteracting equipment uses the first LUT to counteract amplitude distortion in the signal handling equipment; and
X e(n−1) (ƒ(A 1 )) is amplitude of the average error signal corresponding to ƒ(A 1 )).
31. The invention of claim 30 , wherein:
the distortion counteracting equipment uses a second LUT to counteract phase distortion in the signal handling equipment; and
the second LUT is updated according to:
L P(n) (ƒ( A 1 )) =L P(n−1) (ƒ( A 1 )) −r·P e(n−1) (ƒ( A 1 )),
where:
L P(n−1) (ƒ(A 1 )) is the previous value stored in the second LUT for index ƒ(A 1 );
L P(n)(ƒ(A 1 )) is the updated value stored in the second LUT for index ƒ(A 1 ); and
P e(n−1) (ƒ(A 1 )) is phase of the average error signal corresponding to ƒ(A 1 )).
32. The invention of claim 29 , wherein:
the distortion counteracting equipment uses the first LUT to counteract in-phase distortion in the signal handling equipment; and
X e(n−1) (ƒ(A 1 )) is an in-phase component of the average error signal corresponding to ƒ(A 1 )).
33. The invention of claim 29 , wherein:
the distortion counteracting equipment uses the first LUT to counteract quadrature distortion in the signal handling equipment; and
X e(n−1) (ƒ(A 1 )) is a quadrature component of the average error signal corresponding to ƒ(A 1 )).