Digital I/Q imbalance compensation

• US 6,330,290 B1
• Filed: 09/25/1998
• Issued: 12/11/2001
• Est. Priority Date: 09/25/1998
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Glas, Jack P.
• Primary Examiner(s): Le, Amanda T.
• Application Number:
  US09/161,164
• Time in Patent Office: 1,173 Days
• Field of Search: 375/219, 375/271, 375/279, 375/322, 375/324, 375/329, 375/344, 455/313-315, 455/317, 455/318, 455/323, 455/324, 455/334, 455/337-341, 455/255-265, 455/296, 455/307-312, 455/115-116, 455/126, 329/304, 329/318, 329/241, 329/306
• US Class Current: 375/324
• CPC Class Codes: H03D 3/009 Compensating quadrature phase or amplitude imbalances
• CPC Class Codes: H03D 7/18 Modifications of frequency-changers for eliminating image frequencies H03D7/16 takes precedence
• CPC Class Codes: H04B 1/28 the receiver comprising at least one semiconductor device having three or more electrodes
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 2027/0024 at the receiver end

Abstract

In a communications terminal that has an image reject mixing arrangement, a compensation system provides compensation for phase and amplitude imbalances, which are caused by a demodulating local oscillator employed in the communications terminal. The image reject mixing arrangement comprises a radio-frequency (RF) mixing stage including an in-phase and a quadrature phase branch, which is configured to receive a radio frequency signal and down convert the radio frequency signal to in-phase and quadrature phase intermediate frequency (IF) signals. It also includes a phase splitter unit coupled to the radio-frequency (RF) mixing stage and configured to provide an in-phase local oscillator signal and a quadrature phase local oscillator signal to the RF mixing stage. The phase splitter causes an amplitude imbalance signal Δ and a phase imbalance signal φ to be generated in the in-phase and quadrature phase branch of the RF mixing stage. A phase splitter compensation unit is coupled to the RF mixing stage and is configured to multiply the in-phase and quadrature phase signals provided by the RF mixing stage by a predetermined compensation factor. An intermediate frequency (IF) mixing stage is coupled to the radio-frequency mixing stage via the phase splitter compensation unit. The IF mixing stage is configured to convert the intermediate signals received from the RF mixing stage to base band frequency region.

Claims

1. In a communications terminal having an image reject mixing arrangement a compensation system for providing compensation for phase and amplitude imbalances caused by a demodulating local oscillator employed in the communications terminal, said compensation system comprising:

a radio-frequency (RF) mixing stage including an in-phase and a quadrature phase branch, configured to receive a radio frequency signal and down convert said radio frequency signal to in-phase and quadrature phase intermediate frequency (IF) signals;

a phase splitter unit coupled to said radio-frequency (RF) mixing stage and configured to provide an in-phase local oscillator signal and a quadrature phase local oscillator signal to said RF mixing stage, said phase splitter causing an amplitude imbalance signal Δ and

a phase imbalance signal φ

to be generated in said in-phase and quadrature phase branch of said RF mixing stage;

a processing circuit coupled to said RF mixing stage and configured to measure a first value associated with said amplitude imbalance and a second value associated with said phase imbalance;

a phase splitter compensation unit coupled to said RF mixing stage and configured to multiply said in-phase and quadrature phase signals provided by said RF mixing stage by a predetermined compensation factor associated with said measured first and second values; and

an intermediate frequency (IF) mixing stage coupled to said radio-frequency mixing stage via said phase splitter compensation unit, said IF mixing stage configured to convert said intermediate signals received from said RF mixing stage to base band frequency region.

2. The communications terminal in accordance with claim 1, further comprising a switching unit coupled to said RF mixing stage and configured to receive a test tone signal and provide said test tone signal to said RF mixing stage.

3. The communications terminal in accordance with claim 2, further comprising a signal processing unit coupled to said IF mixing stage and configured to measure in-phase and quadrature phase components of test tone signal and an image signal caused by said amplitude imbalance Δ

and phase imbalance φ

.

4. The communication terminal in accordance with claim 3, wherein said signal processing unit provides said compensation factors to said compensation unit based on measurements made in response to said test tone signal.

5. The communication terminal in accordance with claim 3, wherein each of said in-phase and quadrature phase branches of said RF mixing stage further comprises:

a mixer configured to receive radio-frequency signals, and a corresponding in-phase and quadrature phase local oscillator signal to convert said radio-frequency signal to an intermediate frequency (IF) region signal;

a low-pass filter coupled to said mixer; and

an analog-to-digital converter coupled to said low-pass filter.

6. The communication terminal in accordance with claim 3, wherein said in-phase branches of said IF mixing stage further comprises:

a first and a second mixer configured to receive signals provided by said RF mixing stage so as to mix said in-phase signal of said RF mixing stage with an in-phase and quadrature phase local IF oscillator signal; and

a third and a fourth mixer configured to receive said quadrature phase signal of said RF mixing stage so as to mix said quadrature phase signal of said RF mixing stage with an in-phase and quadrature phase local IF oscillator signal.

7. A communication terminal in accordance with claim 6 further comprising:

a first adder configured to receive signals provided by said first and fourth mixer of said IF mixing stage, said first adder providing a signal to said signal processing unit via a digital filter; and

a second adder configured to receive signals provided by said second and third mixer of said IF mixing stage, said second adder providing a signal to said signal processing unit via digital filter.

8. A communication terminal in accordance with claim 7 wherein said compensation unit comprises:

a first multiplier coupled to an output port of said in-phase branch of said RF mixing stage so as to provide a compensation factor β

;

a second multiplier coupled to an output port of said quadrature phase branch of said RF mixing stage so as to provide a compensation factor α

; and

an adder coupled to said first and second multiplier so as to provide a compensation signal to said quadrature branch of said IF mixing stage.

9. A communication terminal in accordance with claim 8 wherein said compensation factor α

and β

is calculated based on $\begin{array}{c}\mathrm{\alpha <br><br>}=\frac{1}{\left(1-{\mathrm{\Delta <br><br>}}_{\mathrm{total}}\right)<br><br>\cos <br><br>\left({\mathrm{\phi <br><br>}}_{\mathrm{total}}\right)}\\ \mathrm{\beta <br><br>}=-\tan <br><br>\left({\mathrm{\phi <br><br>}}_{\mathrm{total}}\right).\end{array}$

10. A communication terminal in accordance with claim 8 wherein said compensation factors α

and β

is derived as

11. In a communications terminal having an image reject mixing arrangement a compensation system for providing compensation for phase and amplitude imbalances caused by a demodulating local oscillator employed in the communications terminal, said compensation system comprising:

a radio-frequency (RF) mixing stage including an in-phase and a quadrature phase branch, configured to receive a radio frequency signal and down convert said radio frequency signal to in-phase and quadrature phase intermediate frequency (IF) signals;

a phase splitter unit coupled to said radio-frequency (RF) mixing stage and configured to provide an in-phase local oscillator signal and a quadrature phase local oscillator signal to said RF mixing stage, said phase splitter causing an amplitude imbalance signal Δ and

a phase imbalance signal φ

to be generated in said in-phase and quadrature phase branch of said RF mixing stage;

a processing circuit coupled to said RF mixing stage and configured to measure a first value associated with said amplitude imbalance and a second value associated with said phase imbalance;

a phase splitter compensation unit coupled to said RF mixing stage and configured to multiply said in-phase and quadrature phase signals provided by said RF mixing stage by a predetermined compensation factor associated with said measured first and second values;

an intermediate frequency (IF) mixing stage coupled to said radio-frequency mixing stage via said phase splitter compensation unit, said IF mixing stage configured to convert said intermediate signals received from said RF mixing stage to base band frequency region; and

a transmitter stage coupled to said RF mixing stage and configured to provide a test tone signal to said RF mixing stage.

12. The communications terminal in accordance with claim 11, wherein said transmitter stage further comprises:

a first transmission mixing stage having a first and a second transmission mixer configured to mix a base band test tone signal with a signal generated by an offset local oscillator; and

a second transmission mixing stage coupled to said first transmission mixing stage, for mixing the signal provided by said first transmission mixing stage with a signal generated by a transmission local oscillator.

13. The communications terminal in accordance with claim 12 further comprising a phase splitter coupled to said offset local oscillator for providing an in-phase and a quadrature phase mixing signal to said first and second transmission mixers.

14. The communications terminal in accordance with claim 13, wherein said phase splitter is a divide-by-four unit.

15. The communications terminal in accordance with claim 14, further comprising a switching unit coupled to said RF mixing stage and configured to receive said test tone signal and provide said test tone signal to said RF mixing stage.

16. The communications terminal in accordance with claim 15, further comprising a signal processing unit coupled to said IF mixing stage and configured to measure in-phase and quadrature phase components of test tone signal and an image signal caused by said amplitude imbalance Δ

and phase imbalance φ

.

17. The communication terminal in accordance with claim 16, wherein said signal processing unit provides said compensation factors to said compensation unit based on measurements made in response to said test tone signal.

18. The communication terminal in accordance with claim 16, wherein each of said in-phase and quadrature phase branches of said RF mixing stage further comprises:

a mixer configured to receive radio-frequency signals, and a corresponding in-phase and quadrature phase local oscillator signal to convert said radio-frequency signal to an intermediate frequency (IF) region signal;

a low-pass filter coupled to said mixer; and

an analog-to-digital converter coupled to said low-pass filter.

19. The communication terminal in accordance with claim 18, wherein said in-phase branches of said IF mixing stage further comprises:

a first and a second mixer configured to receive signals provided by said RF mixing stage so as to mix said in-phase signal of said RF mixing stage with an in-phase and quadrature phase local IF oscillator signal; and

a third and a fourth mixer configured to receive said quadrature phase signal of said RF mixing stage so as to mix said quadrature phase signal of said RF mixing stage with an in-phase and quadrature phase local IF oscillator signal.

20. A communication terminal in accordance with claim 19 further comprising:

a first adder configured to receive signals provided by said first and fourth mixer of said IF mixing stage, said first adder providing a signal to said signal processing unit via digital filter; and

a second adder configured to receive signals provided by said second and third mixer of said IF mixing stage, said second adder providing a signal to said signal processing unit via digital filter.

21. A communication terminal in accordance with claim 20 wherein said compensation unit comprises:

a first multiplier coupled to an output port of said in-phase branch of said RF mixing stage so as to provide a compensation factor β

;

a second multiplier coupled to an output port of said quadrature phase branch of said RF mixing stage so as to provide a compensation factor α

; and

an adder coupled to said first and second multiplier so as to provide a compensation signal to said quadrature branch of said IF mixing stage.

22. A communication terminal in accordance with claim 21 wherein said compensation factor α

and β

is calculated based on $\begin{array}{c}\mathrm{\alpha <br><br>}=\frac{1}{\left(1-{\mathrm{\Delta <br><br>}}_{\mathrm{total}}\right)<br><br>\cos <br><br>\left({\mathrm{\phi <br><br>}}_{\mathrm{total}}\right)}\\ \mathrm{\beta <br><br>}=-\tan <br><br>\left({\mathrm{\phi <br><br>}}_{\mathrm{total}}\right).\end{array}$

23. A communication terminal in accordance with claim 21 wherein said compensation factors α

and β

is derived as

24. In a communications terminal employing an image-rejection system a method for compensating image signals caused by local oscillator of said communications terminal comprising the steps of:

receiving a radio frequency signal and down converting said radio frequency signal in a radio-frequency (RF) mixing stage so as to provide in-phase and quadrature phase intermediate frequency (IF) signals;

providing an in-phase local oscillator signal and a quadrature phase local oscillator signal to said RF mixing stage via a phase splitter that causes said image signals that are compensated, said phase splitter causing an amplitude imbalance signal Δ and

a phase imbalance signal φ

;

measuring, via a processing circuit coupled to said RF mixing stage, a first value associated with said amplitude imbalance and a second value associated with said phase imbalance;

multiplying said in-phase and quadrature phase signals provided by said RF mixing stage by a predetermined compensation factor associated with said measured first and second values; and

converting said intermediate signals received from said RF mixing stage to base band frequency region via an intermediate frequency (IF) mixing stage coupled to said radio-frequency mixing stage.

25. The method in accordance with claim 24, further comprising the step of receiving a test tone signal and providing said test tone signal to said RF mixing stage.

26. The method in accordance with claim 25, further comprising the step of measuring in-phase and quadrature phase components of said test tone signal and an image signal caused by said amplitude imbalance Δ

and phase imbalance φ

.

27. The method in accordance with claim 26, further comprising the step of providing said compensation factors to said compensation unit based on measurements made in response to said test tone signal.

28. The method in accordance with claim 27, wherein said step of multiplying further comprises the step of calculating a first and a second compensation factor α

and β

based on $\begin{array}{c}\mathrm{\alpha <br><br>}=\frac{1}{\left(1-{\mathrm{\Delta <br><br>}}_{\mathrm{total}}\right)<br><br>\cos <br><br>\left({\mathrm{\phi <br><br>}}_{\mathrm{total}}\right)}\\ \mathrm{\beta <br><br>}=-\tan <br><br>\left({\mathrm{\phi <br><br>}}_{\mathrm{total}}\right).\end{array}$

29. The method in accordance with claim 27 wherein said step of multiplying further comprises the step of calculating a first and a second compensation factor α

and β

based on