When using an external analog quadrature mixer device, a pair of converters (either RF-ADC or RF-DAC) must be used to handle the I and Q datapaths after conversion. Due to external events or circumstances, errors or imbalances can be introduced in the analog I and Q signal paths which, if not corrected, can lead to system performance degradation. The necessary corrections to restore any system from degrading are accomplished using the quadrature modulator correction (QMC) circuit.
As shown in the following figure, the QMC circuit is for correction only. Error and/or imbalance detection must be done by application-specific code in the internal interconnect logic.
The QMC circuit can compensate for the following:
- Gain correction is done by multiplying the signal by a gain factor. This factor has a range of 0 to 2.0, and individual factors can be applied to the I and Q datapaths. The output resolution of the block is 16 bits.
- Phase correction is achieved by adding a scaled fraction of Q to the I value. The result of this addition can result in a gain error that must be corrected by the gain error correction block. Phase correction has a range of approximately ±26 degrees.
- Offset correction is done by adding a fixed LSB value to the sampled signal. Range is -2048 to 2047
For full QMC functionality, a pair of converters need to be set up and used in I/Q mode. When disabling the phase correction factor, the QMC block can supply gain and offset correction to a converter used in real mode. In this case, the converters do not need to be paired to make use of the QMC block functions.