I/Q imbalance calibration in wideband direct-conversion receivers

A wideband correction technique is proposed to calibrate the I/Q imbalance of wideband direct-conversion receivers (DCR). The wide bandwidth of input signal is divided into a series of narrow-band in which the I/Q mismatches are frequency-dependent. By using test signals in above narrow-band, the correction coefficients a and b can be calculated at corresponding frequencies. And then the coefficient curves over the whole wideband can be obtained based on cubic spline interpolation. With this method, the image rejection ratio (IRR) of DCR is generally increased 30dBc in the whole band after calibration, and the performance is improved significantly.