System and method for I-Q mismatch compensation in a low IF or zero IF receiver

An apparatus for compensation of circuit mismatch in a low IF or zero IF receiver, comprising:

• mixer means for mixing modulated radio frequency (RE) signals from RF to baseband or near-baseband;
• filter means coupled to an output of the mixer means for filtering signals genetated by the mixer means
• wherein the mixer means and/or the filter means have gain and/or phase error that result in undesired signal components in an output signal of the filter means;
• and
• compensation means for automatically applying a correction factor to the output signal of the filter means by applying a multiplication factor to the output signal to thereby generate a corrected signal,
• wherein the apparatus for compensation of circuit mismatch is implemented in a quadrature receiver, the mixer means comprising:
• first mixer means having a radio frequency (RF) input, a local oscillator input and a mixer output, the RF inputs of the first mixer means being configured to receive modulated RF signals, the local oscillator input of the first mixer means being configured to receive an I local oscillator signal;
• and
• second mixer means having a radio frequency (RF) input, a local oscillator input and a mixer output, the RF inputs of the second mixer means being configured to receive modulated RE signals, the local oscillator input of the second mixer means being configured to receive a Q local oscillator signal having a frequency substantially equal to a frequency of the I local oscillator signal.

A method for compensation of I-Q mismatch in a low IF or zero IF CDMA receiver, comprising:

• injecting a plurality of radio frequency (RF) signals of different frequencies into RF inputs of first and second mixers;
• injecting an I local oscillator signal into a local oscillator input of the first mixer;
• injecting a Q local oscillator signal into a local oscillator input of the second mixer;
• for each of the plurality of RF signals, coupling outputs of the first and second mixers to filter inputs, respectively, of first and second filters;
• for each of the plurality of RF signals, measuring gain and/or phase errors in filter output signals of at least one of the first and second filters;
• and
• determining a correction factor to apply to at least one of the filter output signals to correct the gain and/or phase error.

A computer-readable media for compensation of I-Q mismatch in a low IF or zero IF CDMA receiver by instructing a computer system to:

• inject a plurality of radio frequency (RF) signals of different frequencies into RF inputs of first and second mixers;
• inject an I local oscillator signal into a local oscillator input of the first mixer,
• inject a Q local oscillator signal into a local oscillator input of the second mixer;
• for each of the plurality of RF signals coupled from outputs of the first and second mixers to filter inputs, respectively, of first and second filters, measure gain and/or phase errors between filter output signals;
• and
• determine a correction factor to apply to at least one of the filter output signals to correct the gain and/or phase error.