Method and apparatus for I/Q imbalance compensation
Various embodiments are disclosed relating to a wireless transceiver. In an example embodiment, a method of compensating for phase imbalance and amplitude imbalance between corresponding in-phase signals and quadrature-phase signals includes providing a plurality of test tones of various frequencies to a receiver and determining, for each of the test tones, a respective phase imbalance and a respective amplitude imbalance between an in-phase (I) signal and a quadrature-phase (Q) signal of the test tone. The example method also includes determining a set of filter coefficients based on the determined phase and amplitude imbalances of the plurality of test tones and applying the set of filter coefficients to a plurality of filters. In the example method, a phase imbalance between an I signal and a Q signal of a received wireless signal is compensated for using a first filter of the plurality of filters. Further, an amplitude imbalance between the I and Q signals of the received wireless signal is compensated for using a second filter of the plurality of filters.
1. A method of compensating for phase imbalance and amplitude imbalance between corresponding in-phase signals and quadrature-phase signals in a wireless receiver, the method comprising:
providing a plurality of test tones of various frequencies to the receiver;
determining, for each of the test tones, a respective phase imbalance and a respective amplitude imbalance between an in-phase signal and a quadrature-phase signal of the test tone, the respective phase imbalance and the respective amplitude imbalance each having a frequency dependent component;
determining a set of filter coefficients based on the determined phase and amplitude imbalances of the plurality of test tones;
applying the set of filter coefficients to a plurality of filters;
compensating for a frequency dependent phase imbalance between an in-phase signal and a quadrature-phase signal of a received wireless signal using a first filter of the plurality of filters; and
compensating for a frequency dependent amplitude imbalance between the in-phase signal and the quadrature-phase signal of the received wireless signal using a second filter of the plurality of filters.
2. The method of claim 1 , wherein the plurality of test tones is provided to the receiver in response to an indication that a sending entity wishes to send the wireless signal, the indication including a paging signal from one of a base station and an access point.
3. The method of claim 2 , wherein the wireless signal comprises a first data packet.
4. The method of claim 3 , wherein the plurality of test tones is provided to the receiver prior to receiving the first data packet; and
a subset of the plurality of test tones is provided to the receiver after the receiver receives the first data packet and before the receiver receives additional data packets.
5. The method of claim 1 , wherein the first filter compensates for the phase imbalance asymmetrically and the second filter compensates for the amplitude imbalance asymmetrically.
6. The method of claim 1 , further comprising:
compensating for a frequency independent phase imbalance between the in-phase signal and the quadrature-phase signal of the received wireless signal using the first filter; and
compensating for a frequency independent amplitude imbalance between the in-phase signal and the quadrature-phase signal of the received wireless signal using the second filter.
7. The method of claim 1 , wherein the plurality of test tones is provided to the receiver from a transmitter portion of a wireless transceiver, the wireless transceiver including the receiver.
8. The method of claim 1 , wherein determining the respective phase imbalance and the respective amplitude imbalance between the in-phase signal and the quadrature-phase signal for each test tone comprises, per test tone:
providing a digital in-phase reference signal and a digital quadrature-phase reference signal corresponding with the test tone, wherein the digital in-phase reference signal and the digital quadrature-phase reference signal represent an in-phase signal and a quadrature-phase signal at a frequency of the test tone with substantially equal magnitude and substantially 90 degree phase separation with respect to each other;
mixing the in-phase signal and the quadrature-phase signal of the test tone with the digital in-phase reference signal and the digital quadrature-phase reference signal to produce a plurality of mixed signals; and
filtering and processing the plurality of mixed signals to determine the phase imbalance and the amplitude imbalance between the in-phase signal and the quadrature-phase signal of the test tone.
9. The method of claim 8 , wherein filtering and processing the plurality of mixed signals comprises low pass filtering and notching the plurality of mixed signals using a variable sinc filter including an accumulator, a differencer and a decimator, the variable sinc filter being configured based on the frequency of the test tone.
10. The method of claim 8 , wherein:
the first filter comprises a first linear-phase filter; and
the second filter comprises a second linear-phase filter.
11. The method of claim 10 , wherein the plurality of filters also includes an all-pass filter adapted to compensate for group delays of the first linear-phase filter and the second linear-phase filter.
12. The method of claim 10 , wherein the first linear-phase filter and the second linear-phase filter are “Type I” linear-phase filters.
13. A wireless transceiver comprising:
a transmitter adapted to output a series of test tones at various frequencies;
a receiver coupled with the transmitter so as to receive the series of test tones from the transmitter;
an imbalance measurement circuit coupled with the receiver, the imbalance measurement circuit adapted to:
determine a respective phase imbalance and a respective amplitude imbalance between an in-phase signal and a quadrature-phase signal for each test tone of the series of test tones; and
determine a set of filter coefficients based on the determined phase and amplitude imbalances of the series of test tones; and
a plurality of filters adapted to, using the determined filter coefficients, compensate for a phase imbalance and an amplitude imbalance between an in-phase signal and a quadrature-phase signal of a wireless signal received by the wireless transceiver, wherein the plurality of filters comprises:
a first linear-phase filter adapted to compensate for the phase imbalance between the in-phase signal and the quadrature-phase signal of the wireless signal, the first linear-phase filter being coupled between a quadrature-phase signal path and an in-phase signal path in the receiver; and
a second linear-phase filter adapted to compensate for the amplitude imbalance between the in-phase signal and the quadrature-phase signal of the wireless signal, the second linear-phase filter being included in the quadrature-phase signal path.
14. The wireless transceiver of claim 13 , wherein the imbalance measurement circuit comprises:
a reference circuit adapted to provide (i) a digital in-phase reference signal corresponding with each test tone and (ii) a digital quadrature-phase reference signal corresponding with each test tone;
a plurality of mixers coupled with the reference circuit and the receiver, the mixers adapted to, for each test tone:
mix the digital in-phase reference signal corresponding with the test tone with the in-phase signal of the test tone and the quadrature-phase signal of the test tone to generate first and second mixed signals;
mix the digital quadrature-phase reference signal corresponding with the test tone with the in-phase signal of the test tone and the quadrature-phase signal of the test tone to generate third and fourth mixed signals;
a filter adapted to extract respective direct current (dc) signal components from the first, second, third and fourth mixed signals; and
a compensation processor adapted to:
determine, based on the respective dc components of the first, second, third and fourth mixed signals corresponding with each test tone, a respective phase imbalance and a respective amplitude imbalance between the in-phase signal and the quadrature-phase signal for each test tone; and
determine the set of filter coefficients based on the determined phase and amplitude imbalances of the series of test tones.
15. The wireless transceiver of claim 14 , wherein the reference circuit comprises a Coordinate Rotation Digital Computer (CORDIC), the CORDIC comprising at least one of hardware, software and firmware.
16. The wireless transceiver of claim 13 , wherein the plurality of filters further comprises an all-pass filter adapted to compensate for group delays of the first and second linear-phase filters, the all-pass filter being included in the in-phase signal path.
17. The wireless transceiver of claim 13 , wherein the first and second linear-phase filters are “Type I” linear-phase filters.
18. A method of compensating for imbalance between in-phase signals and corresponding quadrature-phase signals in a wireless transceiver, the method comprising:
responsive to an indication that a sending entity wishes to transmit a wireless signal to the wireless transceiver, providing a plurality of test tones from a transmitter portion of the wireless transceiver to a receiver portion of the wireless transceiver;
for each of the test tones:
providing a digital in-phase reference signal and a digital quadrature-phase reference signal corresponding with the test tone, wherein the digital in-phase reference signal and the digital quadrature-phase reference signal represent an in-phase signal and a quadrature-phase signal at a frequency of the test tone with substantially equal magnitude and substantially 90 degree phase separation with respect to each other;
mixing an in-phase signal and a quadrature-phase signal of the test tone with the digital in-phase reference signal and the digital quadrature-phase reference signal to produce a plurality of mixed signals;
filtering and processing the plurality of mixed signals to determine a phase imbalance and an amplitude imbalance between the in-phase signal and the quadrature-phase signal of the test tone;
determining a set of filter coefficients based on the determined phase and amplitude imbalances of the plurality of test tones;
applying the set of filter coefficients to a plurality of filters;
receiving the wireless signal;
compensating for a phase imbalance between an in-phase signal and a quadrature-phase signal of the received wireless signal using a first filter of the plurality of filters; and
compensating for an amplitude imbalance between the in-phase signal and the quadrature-phase signal of the received wireless signal using a second filter of the plurality of filters.
19. The method of claim 18 , wherein filtering and processing the plurality of mixed signals comprises low pass filtering and notching the plurality of mixed signals using a variable sinc filter comprising an accumulator, a differencer and a decimator, the variable sinc filter being configured based on the respective test tone frequency, and
the method further comprises:
compensating for group delays of the first linear-phase filter and the second linear-phase filter using an all-pass filter, wherein the first filter comprises a first “Type-I” linear-phase filter and the second filter comprises a second “Type I” linear-phase filter.