Method and apparatus for providing an enhanced zero-IF receiver architecture for a wireless communications system
View Patent ↗An approach includes injecting a plurality of equal amplitude tones across a frequency band. The approach also includes determining frequency response based on the injected tones, determining an imbalance parameter associated with a quadrature down-converter based on the determined frequency response; determining one or more parameters for wideband quadrature compensation based on the determined frequency response, and compensating an input signal based on the determined imbalance parameter and the determined one or more parameters for the wideband quadrature compensation.
1. A method comprising:
injecting a first set of tone signals into an RF receiver, wherein the first set of tone signals are within a frequency band of the RF receiver;
down-converting the first set of tone signals, and measuring I and Q components of the down-converted tone signals;
determining one or more imbalance characteristics based on the measured I and Q components of the down-converted first set of tone signals;
determining one or more imbalance compensation parameters based on the determined imbalance characteristic(s), wherein the imbalance compensation parameter(s) are formulated for correction of imbalances in I and Q components resulting from down-conversion of RF signals by the RF receiver;
injecting a second set of tone signals into the RF receiver, wherein the second set of tone signals are within the frequency band of the RF receiver;
down-converting the second set of tone signals, and measuring I and Q components of the down-converted tone signals;
determining one or more flatness characteristics based on the measured I and Q components of the down-converted second set of tone signals;
determining a flatness compensation model based on the determined flatness characteristic(s), wherein the flatness compensation model is formulated for applying a flatness correction to the I and Q components of the down-converted RF signals.
2. The method according to claim 1 , further comprising:
receiving an input RF signal;
down-converting the received input RF signal and generating resulting I and Q components of the RF signal; and
performing an imbalance correction on the resulting I and Q components of the down-converted the RF signal based on the imbalance compensation parameters.
3. The method according to claim 2 , further comprising:
applying a flatness correction to the resulting I and Q components of the down-converted the RF signal based on the flatness compensation model.
4. The method according to claim 1 , further comprising:
determining one or more DC offset parameters based on the measured I and Q components of the down-converted tone signals, wherein the DC offset parameter(s) are formulated to correct for DC offset of the I and Q components resulting from the down-conversion of RF signals by the RF receiver.
5. The method according to claim 4 , further comprising:
receiving an input RF signal;
down-converting the received input RF signal and generating resulting I and Q components of the RF signal;
performing an imbalance correction of the resulting I and Q components of the down-converted the RF signal based on the imbalance compensation parameters; and
applying a DC offset to the resulting I and Q components of the down-converted the RF signal based on the DC offset parameter(s).
6. The method according to claim 5 , further comprising:
applying a flatness correction to the resulting I and Q components of the down-converted the RF signal based on the flatness compensation model.
7. The method according to claim 1 , wherein the determination of the imbalance compensation parameters comprises formulating filter coefficients for a filter to reflect an inverse of the imbalance characteristics.
8. The method according to claim 7 , wherein the filter is configured as one or more finite impulse response (FIR) filters.
9. The method according to claim 1 , wherein the determination of the flatness compensation model comprises formulating coefficients for a filter to generate a spectrum that reflects an inverse of the flatness characteristic(s).
10. The method according to claim 9 , wherein the filter is configured as one or more finite impulse response (FIR) filters.
11. An apparatus comprising:
a quadrature down-converter configured to down-convert an input RF signal to generate resulting I and Q components of the RF signal;
a wideband quadrature compensator configured to compensate for imbalances in the I and Q components of the down-converted RF signal based on one or more imbalance compensation parameters; and
a wideband flatness compensator configured to apply a flatness correction to the I and Q components of the down-converted RF signal based on a flatness compensation model; and
wherein the one or more imbalance compensation parameters are formulated based on one or more determined imbalance characteristics, wherein the imbalance characteristic(s) are based on measured I and Q components resulting from a down-conversion of a first set of tone signals by the quadrature down-converter; and
wherein the flatness compensation model is formulated based on one or more flatness characteristics, wherein the flatness characteristic(s) are based on measured I and Q components resulting from a down-conversion of a second set of tone signals by the quadrature down-converter.
12. The apparatus according to claim 10 , further comprising:
a DC offset compensator configured to compensate for DC offsets in the I and Q components of the down-converted RF signal based on one or more DC offset parameters, wherein the DC offset parameter(s) are formulated based on the measured I and Q components of the down-converted tone signals.
13. The apparatus according to claim 12 , wherein:
the DC offset compensator comprises a DC offset compensator located within each of an I-branch output and a Q-branch output of the quadrature down-converter, wherein each of the I-branch and Q-branch DC offset compensators is configured to compensate for DC offsets in the respective I and Q components of the down-converted RF signal based on the DC offset parameters for the respective I-branch or Q-branch; and
the wideband quadrature compensator comprises a Q-branch filter located within the Q-branch configured with Q-filter coefficients, a Q/I-branch filter located within a Q-to-I cross-coupled branch from the Q-branch to the I-branch, and a delay device located within the I-branch, wherein the Q-branch and the Q/I-branch filters are each configured with filter coefficients based on respective ones of the imbalance compensation parameters to model an inverse of the imbalance characteristic(s), and the delay device is configured to compensate for a delay corresponding to the Q-branch and the Q/I-branch filters.
14. The apparatus according to claim 12 , wherein:
the DC offset compensator comprises a DC offset compensator located within each of an I-branch output and a Q-branch output of the quadrature down-converter, wherein each of the I-branch and Q-branch DC offset compensators is configured to compensate for DC offsets in the respective I and Q components of the down-converted RF signal based on the DC offset parameters for the respective I-branch or Q-branch; and
the wideband quadrature compensator comprises an I-branch filter located within the I-branch configured with I-filter coefficients, an I/Q-branch filter located within an I-to-Q cross-coupled branch from the I-branch to the Q-branch, and a delay device located within the Q-branch, wherein the I-branch and the I/Q-branch filters are each configured with filter coefficients based on respective ones of the imbalance compensation parameters to model an inverse of the imbalance characteristic(s), and the delay device is configured to compensate for a delay corresponding to the I-branch and the I/Q-branch filters.
15. The apparatus according to claim 11 , wherein the wideband quadrature compensator comprises a filter configured to model an inverse of the imbalance characteristic(s).
16. The apparatus according to claim 15 , wherein the filter comprises one or more finite impulse response (FIR) filters.
17. The apparatus according to claim 11 , wherein the wideband flatness compensator comprises a filter with a spectrum that reflects an inverse of the flatness characteristics.
18. The apparatus according to claim 17 , wherein the filter comprises one or more finite impulse response (FIR) filters.
19. An RF receiver comprising:
an input configured to receive an input RF signal;
one or more bandpass filters configured to attenuate out of band signals from the RF signal;
one or more of a linear RF amplifier configured to apply a linear amplification to the RF signal and an automatic gain controller configured to provide a controlled amplitude signal based on the RF signal;
a quadrature down-converter configured to down-convert the RF signal to generate resulting I and Q components of the RF signal;
a wideband quadrature compensator configured to compensate for imbalances in the I and Q components of the down-converted RF signal based on one or more imbalance compensation parameters; and
a wideband flatness compensator configured to apply a flatness correction to the I and Q components of the down-converted RF signal based on a flatness compensation model; and
wherein the imbalance compensation parameter(s) are formulated based on one or more determined imbalance characteristics, wherein the imbalance characteristic(s) are based on measured I and Q components resulting from a down-conversion of a first set of tone signals by the quadrature down-converter, and wherein the first set of tone signals are within a frequency band of the RF receiver; and
wherein the flatness compensation model is formulated based on one or more flatness characteristics, wherein the flatness characteristic(s) are based on measured I and Q components resulting from a down-conversion of a second set of tone signals by the quadrature down-converter, and wherein the second set of tone signals are within the frequency band of the RF receiver.