Signal processing means
View Patent ↗A non-linearity generator operates on a signal between a frequency converter and an amplifier and acts as a postdistorter for the component it follows and as a predistorter for the component it precedes, thus linearizing the overall input-output characteristic of the circuit. Cross-modulation components distorting an injected pilot signal provide a feed-back signal that is used to control the distortion applied by a non-linearity generator. The non-linearity generator can be adapted to cope with widely spaced input tones. The circuit may form part of a transmitter or a receiver.
1. Signal processing apparatus comprising:
a signal amplifier and a frequency converter which operate in succession on an input signal,
a pilot signal generator adapted to introduce a pilot signal into the input signal prior to frequency conversion and amplification, and
a lineariser which is provided between the amplifier and the frequency converter to introduce a correction signal that is adapted to make the overall input and output characteristic of the apparatus more linear by linearising both the amplifier and frequency converter, wherein:
a feedback signal, derived from the output of the apparatus and containing distortion components from the pilot signal produced by at least one of the frequency converter and the amplifier, is used by the lineariser to adapt the correction signal,
the pilot signal is removed from the output of the apparatus by a filter or by the introduction of a pilot cancellation signal,
the lineariser comprises a distortion generator for producing the correction signal from the output signal of whichever of the amplifier and the frequency converter precedes it, and
the distortion generator comprises a non-linearity generator arranged to generate a third-order non-linearity by mixing the input to the non-linearity generator with itself and then with its input.
2. A signal processing apparatus according to claim 1 , wherein the pilot signal is one of a CW carrier signal, a full carrier AM signal, a suppressed carrier AM, signal a single sideband signal, a quadrature amplitude modulated signal, a filtered quadrature phase shift keyed signal, a direct sequence spread spectrum signal, and a frequency hopped carrier signal modulated with any of the foregoing kinds of signal.
3. Signal processing apparatus according to claim 1 , wherein the pilot signal is one of a two-tone pilot signal and a multi-tone pilot signal.
4. Signal processing apparatus according to claim 1 , wherein the pilot cancellation signal is adjusted using feedback derived from the output of the apparatus.
5. Signal processing apparatus according to claim 1 , wherein the pilot cancellation signal comprises a frequency converted, phase shifted and amplitude adjusted version of the pilot signal.
6. Signal processing apparatus according to claim 1 , wherein a digital signal processor is used to control the pilot cancellation signal using feedback from the output of the signal processing apparatus.
7. Signal processing apparatus according to claim 1 , further comprising a suppressor for cancelling signals which are images of the pilot signal.
8. Signal processing apparatus according to claim 1 , wherein a digital signal processor is used to control the correction signal using feedback from the output of the signal processing apparatus.
9. Signal processing apparatus according to claim 1 , wherein the non linearity generator uses at least one of anti-parallel diodes, a FET channel, dual gate GaAsFETs operating close to pinch-off, Shottky diodes, mixers and multipliers in the non-linearity generating process.
10. Signal processing apparatus according to claim 1 , wherein components of the non-linearity are generated and controlled separately.
11. Signal processing apparatus according to claim 10 , wherein in-phase and quadrature signals are produced from each separately generated non-linearity component and are controlled separately.
12. Signal processing apparatus according to claim 1 , wherein the frequency converter comprises a mixer for mixing a mixing signal into a received signal destined to be frequency converted.
13. Signal processing apparatus according to claim 1 , wherein the frequency converter is an upconverter for converting an intermediate frequency band signal into a radio frequency band signal.
14. Signal processing apparatus according to claim 13 , wherein the frequency converter comprises in-phase and quadrature signal paths for handling in-phase and quadrature signals representing a signal at the intermediate frequency band, wherein there is a separate, independently controlled, lineariser operating on each of these signal paths.
15. Signal processing apparatus according to claim 1 , wherein the frequency converter is a downconverter for converting a radio frequency band signal into an intermediate frequency band signal.
16. Signal processing apparatus according to claim 15 , wherein the frequency converter comprises in-phase and quadrature signal paths for handling in-phase and quadrature signals representing a signal at the intermediate frequency band, wherein there is a separate, independently controlled, lineariser operating on each of these signal paths.
17. Signal processing apparatus according to claim 1 , wherein the input signal is a CDMA signal.
18. Signal processing apparatus according to claim 1 , wherein the pilot signal is removed from the output of the apparatus by the filter.
19. Signal processing apparatus according to claim 1 , wherein the pilot signal is removed from the output of the apparatus by the introduction of the pilot cancellation signal.
20. A method of processing an input signal to produce an output signal, the method comprising the steps of:
signal amplification and frequency conversion,
introducing a pilot signal into the input signal prior to frequency conversion aid amplification,
introducing, between the steps of amplification and frequency conversion, a correction signal that is adapted to make the overall input and output characteristic of the signal processing method more linear by linearising both the amplification and frequency conversion,
using a feedback signal, derived from the output signal of the signal processing method and containing distortion components from the pilot signal produced by at least one of the frequency conversion and amplification steps, to adapt the correction signal, and
removing the pilot signal from the output signal of the method by filtering or by introducing a pilot cancellation signal, wherein:
the correction signal is produced by a step of distorting the signal produced by whichever of the amplifying and frequency conversion steps precedes it, and
distorting the signal comprises generating a third-order non-linearity by mixing the input signal with itself and then with the input signal.
21. A method according to claim 20 , comprising the step of adjusting the pilot cancellation signal using feedback derived from the output signal of the signal processing method.
22. A method according to claim 20 , wherein the step of distortion generation comprises the step of generating and controlling non-linearity components independently.
23. A method according to claim 20 , wherein the input signal is a CDMA signal.
24. A method according to claim 20 , further comprising the step of removing the pilot signal from the output signal of the method by filtering.
25. A method according to claim 20 , further comprising the step of removing the pilot signal from the output signal of the method by introducing the pilot cancellation signal.
26. Signal processing apparatus comprising a signal amplifier and a frequency converter which operate in succession on an input signal, and a lineariser which is provided between the amplifier and the frequency converter to introduce a correction signal that is adapted to make the overall input and output characteristic of the apparatus more linear by linearising both the amplifier and frequency converter, wherein:
the lineariser comprises a distortion generator for producing the correction signal from the output signal of whichever of the amplifier and the frequency converter precedes it, and
the distortion generator comprises a non-linearity generator arranged to generate a third-order non-linearity by mixing the input to the non-linearity generator with itself and then with its input.
27. Signal processing apparatus according to claim 26 , wherein the non linearity generator uses at least one of anti-parallel diodes, a FET channel, dual gate GaAsFETs operating close to pinch-off, Shottky diodes, mixers and multipliers in the non-linearity generating process.
28. Signal processing apparatus according to claim 26 , wherein components of the non-linearity are generated and controlled separately.
29. Signal processing apparatus according to claim 28 , wherein in-phase and quadrature signals are produced from each separately generated non-linearity component and are controlled separately.
30. A method of processing an input signal to produce an output signal, the method comprising the steps of signal amplification and frequency conversion, and the step of introducing a correction signal that is adapted to make the overall input and output characteristic of the signal processing method more linear by linearising both the amplification and frequency conversion, wherein:
the correction signal is introduced between the step of signal amplification and the step of frequency conversion;
the correction signal is produced by a step of distorting the signal produced by whichever of the amplifying and frequency conversion steps precedes it,
the step of distortion generation comprises the step of generating and controlling non-linearity components independently, and
the step of distortion generation comprises generating a third-order non-linearity by mixing the input signal with itself and then with the input signal.
31. Signal processing apparatus comprising:
a signal amplifier and a frequency converter which operate in succession on an input signal,
a pilot signal generator adapted to introduce a pilot signal into the input signal prior to frequency conversion and amplification, and
a lineariser which is provided between the amplifier and the frequency converter to introduce a correction signal that is adapted to make the overall input and output characteristic of the apparatus more linear by linearising both the amplifier and frequency converter, wherein:
a feedback signal, derived from the output of the apparatus and containing distortion components from the pilot signal produced by at least one of the frequency converter and the amplifier, is used by the lineariser to adapt the correction signal,
the pilot signal is removed from the output of the apparatus by a filter or by the introduction of a pilot cancellation signal,
the lineariser comprises a distortion generator for producing the correction signal from the output signal of whichever of the amplifier and the frequency converter precedes it,
the distortion generator comprises a non-linearity generator arranged to generate the non-linearity by mixing its input signal with itself one or more times to produce the non-linearity,
components of the non-linearity are generated and controlled separately, and
in-phase and quadrature signals are produced from each separately generated non-linearity component and are controlled separately.