D.C. offset estimation

摘要

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 for the I and Q components. In one embodiment, the “special” phase shift for the I and Q components is 180 degrees and 270 degrees, respectively.

主权项

1. 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 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 about 90 degrees for quadrature modulation in the transmit path, to generate a second pair of oscillator signals having a relative phase shift of about 90 degrees for demodulation in the measurement receiver, and to selectively generate a third pair of oscillator signals having a relative phase shift of about 90 degrees and a phase shift with respect to the second pair of oscillator signals for 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 pairs of oscillator signals.