Receiver I/Q group delay mismatch correction

A device for minimizing group delay mismatch in a quadrature receiver having an in-phase channel and a quadrature-phase channel, the device comprising:

• a processor, coupled to the quadrature receiver, for determining an I/Q phase imbalance between digital signals of the in-phase channel and the digital signals of the quadrature-phase channel, and for calculating, from the phase imbalance, the group delay mismatch between the in-phase channel and the quadrature-phase channel;
• and
• a group delay equalizer, coupled to the processor, including:
• a first multiplexer having an input coupled to the in-phase channel and another input coupled to the quadrature-phase channel of the quadrature receiver, a first control input coupled to the processor, and a first multiplexer output,
• a delay line, coupled to the first multiplexer output of the first multiplexer, for delaying one of the in-phase channel and the quadrature-phase channel by one of a plurality of delays,
• a second multiplexer having a plurality of inputs coupled to the delay line, a second control input coupled to the processor, and a second multiplexer output,
• a third multiplexer having an input coupled to the in-phase channel and another input coupled to the second multiplexer output, a third control input coupled to the processor, and a third multiplexer output, and
• a fourth multiplexer having an input coupled to the quadrature-phase channel and another input coupled to the second multiplexer output, a fourth control input coupled to the processor, and a fourth multiplexer output.

A method of a quadrature receiver having an in-phase channel and a quadrature-phase channel, comprising the steps of:

• determining an I/Q phase imbalance between digital signals of the in-phase channel and the digital signals of the quadrature-phase channel, the digital signals comprising samples;
• calculating, by a group delay equalizer, from the phase imbalance, a group delay mismatch between the in-phase channel and the quadrature-phase channel, the group delay equalizer coupled to a quadrature-phase downsampling filter;
• and
• delaying signals of one of the in-phase channel and the quadrature-phase channel by one or more samples, a number of samples being based upon an amount of the group delay mismatch, such that the group delay equalizer corrects for at least some of the group delay mismatch,
• wherein the quadrature receiver includes a single-tap complex multiplier coupled to an output of the quadrature-phase downsampling filter, and the method includes, subsequent to the step of delaying, a step of multiplying imaginary signals of the quadrature-phase channel with a complex number C0 having a value selected to reduce the I/Q phase imbalance, the single-tap complex multiplier having a real output and an imaginary output, and wherein the real output is added to real signals of the in-phase channel, and
• wherein the complex number C0 is computed determined as follows:
• inject into the quadrature receiver an unmodulated test sinusoid at RF frequency so that ±fCAL are resulting baseband frequencies,
• measure amplitude and phase of the unmodulated test sinusoid of both the in-phase channel and the quadrature-phase channel relative to a common reference sinusoid by correlating the unmodulated test sinusoid with the common reference sinusoid,
• perform a single-bin discrete Fourier transform both the in-phase channel and the quadrature-phase channel to produce two complex values, ICAL and QCAL, and
• compute C0=conjugate{−j*ICAL/QCAL}.