Wide band iq splitting apparatus and calibration method therefor with balanced amplitude and phase between i and q

Abstract

The present invention provides a wide band IQ splitting apparatus suitable for using in a spectrum analyzer. A quadrature oscillator generates a pair of quadrature signals. An amplitude and phase adjuster receives the quadrature signals and adjusts the balances of the amplitude and the phase between them. An analog splitter mixes an analog IF signal with the pair of quadrature signals for splitting the analog IF signal into analog I and Q signals. First and second analog to digital converters and convert the analog I and Q signals into digital I and Q signals, respectively. A control and processing circuit detects the imbalances of the amplitude and phase between the digital I and Q signals for controlling the amplitude and phase adjuster . The amplitude and phase adjuster is previously calibrated. For this first calibration, the analog splitter receives a first calibration signal instead of the analog IF signal. The first calibration signal has a known amplitude and a known frequency slightly different from the frequency of the quadrature signals. Then the control and processing circuit detects the imbalance of the amplitude and/or the phase of the digital I and Q signals and controls the amplitude and phase adjuster properly. The control and processing circuit also produces compensation data. The analog splitter receives a second calibration signal instead of the analog input signal. The frequency of the second calibration signal varies within the band of the analog IF signal. The control and processing circuit calculates the compensation data at a plurality of the frequencies of the calibration signal and a memory stores the compensation data. The compensation data are used to produce compensated frequency domain data, and then compensated time domain data are made from the compensated frequency domain data.