Datasheet
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Quadrature Modulator Correction (QMC)
DAC5687
SLWS164E – FEBRUARY 2005 – REVISED SEPTEMBER 2006
Table 10. Coarse Mixer Sequences
cm_mode(3:0) Mixing Mode Sequence
00XX No mixing
0100 f
DAC
/2 DAC A = { – A +A – A +A … }
DAC B = { – B +B – B +B … }
0101 f
DAC
/2 DAC A = { – A +A – A +A … }
DAC B = {+B – B +B – B … }
0110 f
DAC
/2 DAC A = {+A – A +A – A … }
DAC B = { – B +B – B +B … }
0111 f
DAC
/2 DAC A = {+A – A +A – A … }
DAC B = {+B – B +B – B … }
1000 f
DAC
/4 DAC A = {+A – B – A +B … }
DAC B = {+B +A – B – A … }
1001 f
DAC
/4 DAC A = {+A – B – A +B … }
DAC B = { – B – A +B +A … }
1010 f
DAC
/4 DAC A = { – A +B +A – B … }
DAC B = {+B +A – B – A … }
1011 f
DAC
/4 DAC A = { – A +B +A – B … }
DAC B = { – B – A +B +A … }
1100 – f
DAC
/4 DAC A = {+A +B – A – B … }
DAC B = {+B – A – B +A … }
1101 – f
DAC
/4 DAC A = {+A +B – A – B … }
DAC B = { – B +A +B – A … }
1110 – f
DAC
/4 DAC A = { – A – B +A +B … }
DAC B = {+B – A – B +A … }
1111 – f
DAC
/4 DAC A = { – A – B +A +B … }
DAC B = { – B +A +B – A … }
The output of CMIX is complex. For a real output, either DACA or DACB can be used and the other DAC slept,
the difference being the phase sequence.
The quadrature modulator correction (QMC) block provides a means for changing the phase balance of the
complex signal to compensate for I and Q imbalance present in an analog quadrature modulator. The QMC block
is limited in operation to a clock rate of 320 MSPS.
The block diagram for the QMC block is shown in Figure 40 . The QMC block contains three programmable
parameters. Registers qmc_gain_a and qmc_gain_b control the I and Q path gains and are 11-bit values with a
range of 0 to approximately 2. Note that the I and Q gain can also be controlled by setting the DAC full-scale
output current (see following). Register qmc_phase controls the phase imbalance between I and Q and is a
10-bit value with a range of – 1/2 to approximately 1/2.
LO feedthrough can be minimized by adjusting the DAC offset feature described as follows.
An example of sideband optimization using the QMC block and gain adjustment is shown in Figure 41 . The QMC
phase adjustment in combination with the DAC gain adjustment can reduce the unwanted sideband signal from
~40 dBc to > 65 dBc.
Note that mixing in the CMIX block after the QMC correction destroys the I and Q phase compensation
information from the QMC block.
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