Compensation of a Transmitter Distortion

• US 20130344827A1
• Filed: 03/16/2012
• Published: 12/26/2013
• Est. Priority Date: 03/18/2011
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: ST-Ericcson SA (Telefonaktiebolaget LM Ericsson)
• Inventors: Epifano, Fabio
• Granted Patent: US 9,118,285 B2
• Time in Patent Office: Days
• US Class Current: 455/114.3
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 27/0002 analog front ends; means for connecting modulators, demodulators or transceivers to a transmission line duplex arrangements H04L5/143
• CPC Class Codes: H04L 27/364 Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels

Abstract

There is described a method for compensating the phase and gain distortions of a transmitter analog front end affected by a leakage of a local oscillator. The method comprises generating a single complex tone signal in a digital front end, wherein the generation comprises compensating the signal gain and phase with gain and phase offsets. The method comprises feeding the compensated signal into the transmitter analog front end. The method comprises feeding a corresponding output signal of the transmitter analog front end into a nonlinear component, thereby generating an inter-modulation between the complex tone signal and at least one tone signal due to the local oscillator leakage. The method comprises feeding the output of the nonlinear component into a measurement receiver analog front end. The method comprises filtering the output of the measurement receiver analog front end with a band pass filter in order to isolate the inter-modulation, which is indicative of the distortions introduced by the transmitter analog front end. The method comprises measuring the power of the filtered signal. The method comprises updating the gain and phase offsets according to the measured power, by reducing said measured power. The disclosure also relates, in particular, to a digital front end, to an analog system, to a telecommunication device, to a computer program, and to a storage medium.

Claims

1. A method of providing gain and phase offsets for compensating the phase and gain distortions of a transmitter analog front end, comprising:

generating a single complex tone signal, wherein the generating comprises compensating the signal gain and phase with gain and phase offsets;

sending the compensated signal to the transmitter analog front end;

receiving a corresponding output signal from a receiver analog front end;

filtering the received signal in order to isolate an inter-modulation signal, which is indicative of distortions introduced by the transmitter analog front end;

measuring the power of the filtered signal;

updating the gain and phase offsets, and repeating the generating, sending, receiving, filtering and measuring steps above;

comparing the measured power before and after the updating step; and

selecting the gain and phase offsets associated with the lowest measured power.

2. The method of claim 1 wherein the filtering is carried out using a band pass filter.

3. The method according to claim 1, the gain and phase offsets being initially set to default values depending on the transmitter analog front end.

4. The method according to claim 1, the single generated complex tone signal being of the form:

i_TX-BB(t)=A·

cos(2·

π

·

f_BB·

t), q_TX-BB(t)=A·

sin(2·

π

·

f_BB·

t)

where i_TX-BB and q_TX-BB represent I and Q components of the generated complex tone signal f_BB, f_BB being the frequency of the signal.

5. The method according to claim 4, wherein the filtering is carried out using a band pass filter and the band pass filter is isolating an inter-modulation signal located around frequency 3*f_BB.

6. The method according to claim 4, wherein the filtering is carried out using a band pass filter and the band pass filter is isolating inter-modulation signal located around frequencies 2*f_BB and 3*f_BB.

7. The method according to claim 1, wherein the updating the gain and phase offsets, and repeating the generating, sending, receiving, filtering and measuring steps are repeated until each of the gain and phase offsets has converged.

18. A computer program product comprising one or more stored sequences of instructions that are accessible to a processor and which, when executed by the processor, cause the processor to carry out the steps of claim 1.

19. A non-transitory computer readable storage medium storing a computer program according to claim 18.

8. A digital front end comprising:

a tone generator arranged to generate a single complex tone signal and send it to a transmitter analog front end;

a compensation unit arranged to cause the tone generator to compensate the gain and phase of the single complex tone signal generated by the tone generator;

a filter arranged to filter a signal received from a measurement receiver analog front end;

a power measurement unit arranged to measure the power of a filtered signal output by the filter;

an updating unit arranged to update gain and phase offsets used by the compensation unit; and

a processor arranged to compare values of measured power of the filtered signal associated with different gain and phase offsets and to select the gain and phase offsets associated with the lowest measured power.

9. The digital front end of claim 8, wherein the filter is a band pass filter.

10. The digital front end of claim 8, wherein the compensation unit is arranged to initially set the gain and phase offsets to zero.

11. The digital front end of claim 8 wherein the tone generator is adapted to generate a single complex tone signal of the form:

i_TX-BB(t)=A·

cos(2·

π

·

f_BB·

t), q_TX-BB(t)=A·

sin(2·

π

·

f_BB·

t)

where i_TX-BB and q_TX-BB represent in-phase, I, and quadrature, Q, components of the generated complex tone signal f_BB, f_BB being the frequency of the signal.

12. The digital front end of claim 8 wherein the filter is adapted to isolate an inter-modulation signal located around a frequency of 3*f_BB, f_BB being the frequency of the generated tone signal.

13. The digital front end of claim 8 wherein the filter is adapted to isolate inter-modulation signals located around frequencies of 2*f_BB and 3*f_BB, f_BB being the frequency of the generated tone signal.

14. A telecommunication device comprising a digital front end according to claim 8.

15. The telecommunication device of claim 14 further comprising an analog system comprising:

a transmitter analog front end,

a measurement receiver analog front end,

a local oscillator, and

a nonlinear component adapted to feed an output of the transmitter analog front end into an input of the measurement receiver analog front end.

16. The telecommunication device of claim 15, wherein the nonlinear component comprises a nonlinear amplifier connected between the output of the transmitter analog front end and the input of the measurement receiver analog front end.

17. The telecommunication device of claim 15 further comprising a switching arrangement arranged to selectively feed the output of the transmitter analog front end into the input of the measurement receiver analog front end.