Adaptive parametric signal predistorter for compensation of time varying linear and nonlinear amplifier distortion

• US 5,900,778 A
• Filed: 05/08/1997
• Issued: 05/04/1999
• Est. Priority Date: 05/08/1997
• Status: Expired due to Term

• Current Assignee: John T. Stonick, Jose M.F. Moura, Virginia L. Stonick
• Original Assignee: John T. Stonick, Jose M.F. Moura, Virginia L. Stonick
• Inventors: Stonick, John T., Moura, Jose M. F., Stonick, Virginia L.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): NGUYEN, KHANH V
• Application Number:
  US08/852,944
• Time in Patent Office: 726 Days
• Field of Search: 330/149, 330/107, 332/159, 332/160, 332/161, 332/162, 455/126, 375/296, 375/297
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3258 based on polynomial terms
• CPC Class Codes: H03F 2200/57 Separate feedback of real and complex signals being present
• CPC Class Codes: H03F 2201/3233 Adaptive predistortion using lookup table, e.g. memory, RAM, ROM, LUT, to generate the predistortion

Abstract

A high power amplifier system includes an on-line adaptive predistorter for generating predistorted complex data signals to a high power amplifier in response to receiving incoming complex data signals from a remote source. The predistorted complex data signals enable the high powered amplifier to output signals corresponding to the incoming complex data signals. The amplifier system includes an off-line adaptive predistorter which has an adaptive parametric forward filter for combining predistorted complex data signals and demodulated complex data signals, produced from the output of the high power amplifier, to produce an optimized forward amplitude filter that emulates the forward amplitude response of the amplifier, and an optimized inverse phase filter that emulates the inverse phase response of the amplifier. An adaptive parametric inverse filter combines random amplitude data and the optimized forward amplitude filter of the amplifier to produce an optimized inverse amplitude filter that emulates the inverse amplitude response of the amplifier. An off-line to on-line converter combines the optimized inverse amplitude filter, the optimized inverse phase filter and exemplary complex data to produce the predistorted complex data utilized by the on-line adaptive predistorter for generating the predistorted complex data signals.

Claims

1. An amplifier system comprising:

an on-line adaptive predistorter which receives an incoming complex signal and generates a predistorted complex signal related to the incoming complex signal;

a modulator which receives the predistorted complex signal and produces therefrom a modulated analog signal;

an amplifier which receives the modulated analog signal and produces an amplified modulated analog signal;

a demodulator which demodulates at least a sample of the amplified modulated analog signal and produces therefrom a demodulated complex signal;

an adaptive forward filter which combines the predistorted complex signal and the demodulated complex signal to produce an optimized forward amplitude filter that emulates the forward amplitude response of the amplifier and an optimized inverse phase filter that emulates the inverse phase response of the amplifier;

an adaptive inverse filter which filters an output of the optimized forward amplitude filter to produce an optimized inverse amplitude filter that emulates the inverse amplitude response of the amplifier;

an off-line to on-line converter which combines the response of optimized inverse amplitude filter and the response of optimized inverse phase filter to produce predistorted complex data that is utilized for generating the predistorted complex signal.

2. The amplifier system as set forth in claim 1, wherein the adaptive inverse filter combines (i) random amplitude data and (ii) the optimized forward amplitude filter to produce the output which is utilized to produce the optimized inverse amplitude filter.

3. The amplifier system as set forth in claim 2, wherein:

for each input of random amplitude data the adaptive inverse filter produces a forward amplitude error value which is combined with the random amplitude data to produce an amplitude error value; and

the random amplitude data is selected to cause the adaptive inverse filter to adapt to minimize to a desired extent the amplitude error value.

4. The amplifier system as set forth in claim 3, wherein the adaptive inverse filter includes:

an inverse amplitude filter which filters the random amplitude data to produce filtered random amplitude data; and

a summing circuit which sums the random amplitude data and the forward amplitude error value to produce the amplitude error value, wherein;

the optimized forward amplitude filter is utilized to filter the filtered random amplitude data to produce the forward amplitude error value; and

a curve fitting algorithm is utilized to update the parameters of the inverse amplitude filter to minimize to a desired extent the amplitude error value.

5. The amplifier system as set forth in claim 4, wherein the optimized inverse amplitude filter includes the inverse amplitude filter with updated parameters.

6. The amplifier system as set forth in claim 1, wherein:

the off-line to on-line converter utilizes exemplary complex data to stimulate the response of the optimized inverse amplitude filter and the response of the optimized inverse phase filter to produce the predistorted complex data.

7. The amplifier system as set forth in claim 1, wherein the adaptive forward filter includes:

a rectangular-to-polar converter which converts the predistorted complex signal into a predistorted polar signal and which converts the demodulated complex signal into a demodulated polar signal;

a forward amplitude filter which filters the amplitude portion of the predistorted polar signal and produces a filtered amplitude portion of the predistorted polar signal; and

a summing circuit which combines the filtered amplitude portion of the predistorted polar signal and the amplitude portion of the demodulated polar signal to produce a polar amplitude difference value, wherein;

a curve fitting algorithm is utilized to update the parameters of the forward amplitude filter to minimize to a desired extent the polar amplitude difference value.

8. The amplifier system of claim 7, wherein the optimized forward amplitude filter includes the forward amplitude filter with updated parameters.

9. The amplifier system as set forth in claim 1, wherein the adaptive forward filter includes:

a rectangular-to-polar converter which converts the predistorted complex signal into a predistorted polar signal and which converts the demodulated complex signal into a demodulated polar signal;

an inverse phase filter which filters the amplitude portion of the predistorted polar signal into a filtered phase value;

a first summing circuit which combines the phase portion of the predistorted polar signal and the phase portion of the demodulated polar signal to produce a polar phase difference value; and

a second summing circuit which combines the polar phase difference value and the filtered phase value to obtain a phase error value, wherein;

a curve fitting algorithm is utilized to update the parameters of the inverse phase filter to minimize to a desired extent the phase error value.

10. The amplifier system as set forth in claim 9, wherein the optimized inverse phase filter includes the negative of the inverse phase filter with adapted parameters.

11. The amplifier system as set forth in claim 6, wherein the off-line to on-line converter includes:

a rectangular-to-polar converter which converts the exemplary complex data to exemplary polar data, the amplitude portion of the exemplary polar data is filtered by the optimized inverse amplitude filter to produce an amplitude portion of polar predistorted data the amplitude portion of the polar predistorted data, is filtered by the optimized inverse phase filter to produce inverse phase data;

a summing circuit which combines the phase portion of the exemplary polar data and the inverse phase data to produce a phase portion of polar predistorted data; and

a polar to rectangular converter which converts the amplitude portion of polar predistorted data and the phase portion of polar predistorted data into the predistorted complex data.

12. The amplifier system as set forth in claim 1, wherein the on-line adaptive predistorter includes a lookup table which stores the predistorted complex data and generates therefrom, in response to receiving the incoming complex signal, the predistorted complex signal.

13. A method of determining predistorting data utilized to compensate for nonlinear amplitude and phase distortions of an amplifier, the method comprising the steps of:

(a) converting incoming complex signals to corresponding predistorted complex signals;

(b) modulating the predistorted complex signals to produce modulated analog signals;

(c) amplifying the modulated analog signals to produce amplified analog signals;

(d) demodulating the amplified analog signals to produce demodulated complex signals;

(e) sampling each predistorted complex signal and a temporally corresponding demodulated complex signal; and

(f) combining each predistorted complex signal and each demodulated complex signal to produce predistorting data utilized to generate the predistorted complex signals, wherein step (f) includes the steps of;

converting each predistorted complex signal to predistorted polar data;

converting each demodulated complex signal to demodulated polar data;

generating from the amplitude portion of each predistorted polar data and the temporally corresponding amplitude portion of each demodulated polar data an optimized forward amplitude filter;

generating from the phase portion of each predistorted polar data and the temporally corresponding phase portion of each demodulated polar data an optimized inverse phase filter;

generating from a combination of random amplitude data and the optimized forward amplitude filter an optimized inverse amplitude filter; and

generating the predistorting data from a combination of exemplary data signals, the optimized inverse amplitude filter and the optimized inverse phase filter.

14. The method as set forth in claim 13, further including the steps of:

converting each predistorted complex signal into predistorted polar data and the temporally corresponding demodulated complex signal into demodulated polar data;

sorting the amplitude portions of the predistorted polar signals into one of ascending and descending order;

ordering (i) the amplitude portions of demodulated polar data and (ii) the phase portions of the demodulated polar data based on the sorted indexed of the sorted amplitude portions of the predistorted polar signals;

filtering each of the ordered data in (i) and (ii) to remove measurement noise; and

reordering the data and the signals into original order.

15. A method of updating predistorting data utilized to compensate for nonlinear amplitude and phase distortions of an amplifier, the method comprising the steps of:

(a) supplying incoming complex signals to an active look-up table which stores current predistorted complex data and an inactive look-up table configured to store updated predistorted complex data, with each predistorted complex data corresponding to a predistorted complex signal;

(b) supplying from the active look-up table predistorted complex signals that correspond to the incoming complex signals;

(c) modulating the predistorted complex signals that correspond to the incoming complex signals to produce modulated analog signals;

(d) amplifying the modulated analog signals to produce amplified analog signals;

(e) demodulating the amplified analog signals to produce demodulated complex signals;

(f) sampling each predistorted complex signal and its temporally corresponding demodulated complex signal;

(g) combining each predistorted complex signal and its temporally corresponding demodulated complex signal to produce updated predistorted complex data;

(h) storing each updated predistorted complex data in the inactive look-up table;

(i) deactivating the active look-up table so that it becomes the inactive look-up table; and

(j) activating the inactive look-up table so that it becomes the active look-up table.

16. The method as set forth in claim 15, wherein step (f) includes the steps of:

sampling each predistorted complex signal;

delaying by an interval corresponding to signal propagation delay in steps (c)-(e); and

sampling each temporally corresponding demodulated complex signal.

17. An apparatus for determining predistorting data utilized to compensate for nonlinear amplitude and phase distortions of an amplifier, the apparatus comprising:

a pair of look-up tables connected to receive incoming complex signals and configured to store predistorted complex data, with each predistorted complex data corresponding to a predistorted complex signal;

a controller which causes one of the pair of look-up tables to be active and the other of the pair of look-up tables to be inactive, with the active look-up table supplying predistorted complex signals that correspond to the incoming complex signals;

a modulator which modulates the predistorted complex signals from the active look-up table to produce modulated analog signals;

an amplifier which amplifies the modulated analog signals to produce amplified analog signals;

a demodulator which demodulates the amplified analog signals to produce demodulated complex signals;

a sampler which samples each predistorted complex signal and its temporally corresponding demodulated complex signal; and

a combiner which combines each predistorted complex signal and its temporally corresponding demodulated complex signal to produce updated predistorted complex data, wherein;

the controller causes the updated predistorted complex data to replace the predistorted complex data in the inactive look-up table; and

the controller causes the active look-up table to become inactive and the inactive look-up table to become active.