Datasheet

DAC3484
SLAS749C –MARCH 2011–REVISED AUGUST 2012 www.ti.com
REAL CHANNEL UPCONVERSION
The mixer in the DAC34H84 treats the A, B, C, and D inputs are complex input data and produces a complex
output for most mixing frequencies. The real input data for each channel can be isolated only when the mixing
frequency is set to normal mode or fs/2 mode. Refer to Table 8 for details.
QUADRATURE MODULATION CORRECTION (QMC)
GAIN AND PHASE CORRECTION
The DAC3484 includes a Quadrature Modulator Correction (QMC) block. The QMC blocks provide a mean for
changing the gain and phase of the complex signals to compensate for any I and Q imbalances present in an
analog quadrature modulator. The block diagram for the QMC block is shown in Figure 77. The QMC block
contains 3 programmable parameters.
Register qmc_gainA/B(10:0) and qmc_gainC/D(10:0) controls the I and Q path gains and is an 11-bit unsigned
value with a range of 0 to 1.9990 and the default gain is 1.0000. The implied decimal point for the multiplication
is between bit 9 and bit 10.
Register qmc_phaseAB/CD(11:0) control the phase imbalance between I and Q and is a 12-bit values with a
range of –0.5 to approximately 0.49975. The QMC phase term is not a direct phase rotation but a constant that is
multiplied by each "Q" sample then summed into the "I" sample path. This is an approximation of a true phase
rotation in order to keep the implementation simple. The corresponding phase rotation corresponds to
approximately +26.5 to –26.5 degrees in 4096 steps.
LO feed-through can be minimized by adjusting the DAC offset feature described below.
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