US2011176641A1PendingUtilityA1
D.C. Offset Estimation
Est. expiryJan 20, 2030(~3.5 yrs left)· nominal 20-yr term from priority
Inventors:Jonas Persson
H04L 25/061H04L 27/364H04L 2027/0016H04L 27/2647H04B 1/302H04B 1/0475
43
PatentIndex Score
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Cited by
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Claims
Abstract
A combination of a phase shifter, a measurement receiver, and an offset estimator enable the d.c. offset in the transmit path of a quadrature transmitter to be distinguished from the d.c. offset in the measurement receiver. The measurement receiver performs a first measurement on the transmit path output with a “normal” phase shift of 0 degrees and 90 degrees for in-phase (I) and quadrature (Q) components, and a second measurement with a “special” phase-shift of 180 degrees and 270 degrees for the I and Q components, respectively
Claims
exact text as granted — not AI-modified1 . An apparatus for estimating a direct-current (d.c.) offset in a transmitter having a transmit path for quadrature modulating a carrier with input in-phase (I) and quadrature (Q) component signals and generating a transmit signal, the apparatus comprising:
a measurement receiver, wherein the measurement receiver is configured to quadrature demodulate a portion of the transmit signal to generate an I component measurement signal and a Q component measurement signal; a phase shifter, wherein the phase shifter is configured to generate a first pair of oscillator signals having a relative phase shift of substantially 90 degrees for quadrature demodulation in the measurement receiver and for quadrature modulation in the transmit path, and the phase shifter is configured to selectively generate a second pair of oscillator signals having a relative phase shift of substantially 90 degrees and a phase shift of substantially 180 degrees with respect to the first pair of oscillator signals for quadrature demodulation in the measurement receiver; and an offset estimator, wherein the offset estimator is configured to compute at least one of a d.c. offset of the transmit path and a d.c. offset of the measurement receiver based on the input I and Q component signals and on measurement I and Q component signals generated with the first and second pairs of oscillator signals.
2 . The apparatus of claim 1 , wherein the offset estimator is configured to compute an I component d.c. offset of the measurement receiver according to:
i
D
C
,
MRX
=
i
meas
+
i
meas
2
in which i DC,MRX is the I component of the d.c. offset of the measurement receiver, i meas is the measurement I component signal generated with one of the first pair of oscillator signals, and i meas is the measurement I component signal generated with one of the second pair of oscillator signals having a 180-degree phase shift with respect to the one of the first pair of oscillator signals; and the offset estimator is configured to compute a Q component d.c. offset of the measurement receiver according to:
q
D
C
,
MRX
=
q
meas
+
q
meas
2
in which q DC,MRX is the Q component of the d.c. offset of the measurement receiver, q meas is the measurement Q component signal generated with the other one of the first pair of oscillator signals, and {circumflex over (q)} meas is the measurement Q component signal generated with the other one of the second pair of oscillator signals.
3 . The apparatus of claim 1 , wherein the offset estimator is configured to compute an I component d.c. offset of the transmit path according to:
i
D
C
,
TX
=
i
meas
-
i
meas
-
2
i
ref
2
in which i DC,TX is the I component of the d.c. offset of the transmit path, i meas is the measurement I component signal generated with one of the first pair of oscillator signals, î meas is the measurement I component signal generated with one of the second pair of oscillator signals having a 180-degree phase shift with respect to the one of the first pair of oscillator signals, and i ref is the I component signal; and the offset estimator is configured to compute a Q component d.c. offset of the transmit path according to:
q
D
C
,
TX
=
q
meas
-
q
meas
-
2
q
ref
2
in which q DC,TX is the Q component of the d.c. offset of the transmit path, q meas is the Q component measurement signal generated with the other one of the first pair of oscillator signals, {circumflex over (q)} meas is the measurement Q component signal generated with the other one of the second pair of oscillator signals, and q ref is the Q component signal.
4 . A method of estimating a direct-current (d.c.) offset in a transmitter having a transmit signal generated by quadrature mixing input in-phase (I) and quadrature (Q) component signals with respective ones of a first pair of oscillator signals having a relative phase shift of substantially 90 degrees, the method comprising:
generating a first pair of measurement I component and Q component measurement signals by quadrature demodulating a portion of the transmit signal with the first pair of oscillator signals; generating a second pair of measurement I component and Q component signals by quadrature demodulating a portion of the transmit signal with a second pair of oscillator signals having a relative phase shift of substantially 90 degrees and a relative phase shift with respect to the first pair of oscillator signals of substantially 180 degrees; and computing the d.c. offset based on the first and second pairs of measurement I and Q component signals and on the input I and Q component signals.
5 . The method of claim 4 , wherein computing the d.c. offset includes computing an I component d.c. offset according to:
i
D
C
,
MRX
=
i
meas
+
i
meas
2
in which i DC,MRX is the I component d.c. offset, i meas is the measurement I component signal generated with one of the first pair of oscillator signals, and î meas is the measurement I component signal generated with one of the second pair of oscillator signals having a 180-degree phase shift with respect to the one of the first pair of oscillator signals; and computing the d.c. offset includes computing a Q component d.c. offset according to:
q
D
C
,
MRX
=
q
meas
+
q
meas
2
in which q DC,MRX is the Q component d.c. offset, q meas is the measurement Q component signal generated with the other one of the first pair of oscillator signals, and {circumflex over (q)} meas is the measurement Q component signal generated with the other one of the second pair of oscillator signals.
6 . The method of claim 4 , wherein computing the d.c. offset includes computing an I component d.c. offset of the transmit path according to:
i
D
C
,
TX
=
i
meas
-
i
meas
-
2
i
ref
2
in which i DC,TX is the I component of the d.c. offset of the transmit path, i meas is the measurement I component signal generated with one of the first pair of oscillator signals, î meas is the measurement I component signal generated with one of the second pair of oscillator signals having a 180-degree phase shift with respect to the one of the first pair of oscillator signals, and i ref is the I component signal; and computing the d.c. offset includes computing a Q component d.c. offset of the transmit path according to:
q
D
C
,
TX
=
q
meas
-
q
meas
-
2
q
ref
2
in which q DC,TX is the Q component of the d.c. offset of the transmit path, q meas is the Q component measurement signal generated with the other one of the first pair of oscillator signals, {circumflex over (q)} meas is the measurement Q component signal generated with the other one of the second pair of oscillator signals, and q ref is the Q component signal.
7 . A computer-readable medium having stored instructions that, when executed by a computer, cause the computer to perform a method of estimating a direct-current (d.c.) offset in a transmitter having a transmit signal generated by quadrature mixing input in-phase (I) and quadrature (Q) component signals with respective ones of a first pair of oscillator signals having a relative phase shift of substantially 90 degrees, wherein the method comprises:
generating a first pair of measurement I component and Q component measurement signals by quadrature demodulating a portion of the transmit signal with the first pair of oscillator signals; generating a second pair of measurement I component and Q component signals by quadrature demodulating a portion of the transmit signal with a second pair of oscillator signals having a relative phase shift of substantially 90 degrees and a relative phase shift with respect to the first pair of oscillator signals of substantially 180 degrees; and computing the d.c. offset based on the first and second pairs of measurement I and Q component signals and on the input I and Q component signals.
8 . The medium of claim 7 , wherein computing the d.c. offset includes computing an I component d.c. offset according to:
i
D
C
,
MRX
=
i
meas
+
i
meas
2
in which i DC,MRX is the I component d.c. offset, i meas is the measurement I component signal generated with one of the first pair of oscillator signals, and î meas is the measurement I component signal generated with one of the second pair of oscillator signals having a 180-degree phase shift with respect to the one of the first pair of oscillator signals; and computing the d.c. offset includes computing a Q component d.c. offset according to:
q
D
C
,
MRX
=
q
meas
+
q
meas
2
in which q DC,MRX is the Q component d.c. offset, q meas is the measurement Q component signal generated with the other one of the first pair of oscillator signals, and {circumflex over (q)} meas is the measurement Q component signal generated with the other one of the second pair of oscillator signals.
9 . The medium of claim 7 , wherein computing the d.c. offset includes computing an I component d.c. offset of the transmit path according to:
i
D
C
,
TX
=
i
meas
-
i
meas
-
2
i
ref
2
in which i DC,TX is the I component of the d.c. offset of the transmit path, i meas is the measurement I component signal generated with one of the first pair of oscillator signals, î meas is the measurement I component signal generated with one of the second pair of oscillator signals having a 180-degree phase shift with respect to the one of the first pair of oscillator signals, and i ref is the I component signal; and computing the d.c. offset includes computing a Q component d.c. offset of the transmit path according to:
q
D
C
,
TX
=
q
meas
-
q
meas
-
2
q
ref
2
in which q DC,TX is the Q component of the d.c. offset of the transmit path, q meas is the Q component measurement signal generated with the other one of the first pair of oscillator signals, {circumflex over (q)} meas is the measurement Q component signal generated with the other one of the second pair of oscillator signals, and q ref is the Q component signal.Join the waitlist — get patent alerts
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