Datasheet

NCO _ CLK
NCO
32
freq f
f
2
´
=
Frequency
Register
32
Accumulator
32
RESETCLK
NCO SYNC
via
syncsel_NCO[3:0]
32
32
Phase
Register
16
16
16
Look-Up
Table
sin
cos
ΣΣ
16
16
f
DAC
B0026-03
B0471-02
16 16 16 16
16 16 16 16
sine
16
sine
16
sine
16
cosine
16
cosine
16
cosine
16
Fs/2
Mixer
±Fs/4
Mixer
Complex
Signal
Multiplier
(AB)
Numerically
Controlled
Oscillator
Fixed Fs/8
Oscillator
I Data In
(A)
Q Data In
(B)
I Data Out
(A)
Q Data Out
(B)
CMIX<1> CMIX<2> CMIX<0>
CMIX<3>
NCO_ENA
DAC3484
www.ti.com SLAS749C –MARCH 2011–REVISED AUGUST 2012
COMPLEX SIGNAL MIXER
The DAC3484 has two paths of complex signal mixer blocks that contain two full complex mixer (FMIX) blocks
and power saving coarse mixer (CMIX) blocks. The signal path is shown in Figure 73.
Figure 73. Path of Complex Signal Mixer
FULL COMPLEX MIXER
The two FMIX blocks operate with independent Numerically Controlled Oscillators (NCOs) and enable flexible
frequency placement without imposing additional limitations in the signal bandwidth. The NCOs have 32-bit
frequency registers (phaseaddAB(31:0) and phaseaddCD(31:0)) and 16-bit phase registers (phaseoffsetAB(15:0)
and phaseoffsetCD(15:0)) that generate the sine and cosine terms for the complex mixing. The NCO block
diagram is shown in Figure 74.
Figure 74. NCO Block Diagram
Synchronization of the NCOs occurs by resetting the NCO accumulators to zero. The synchronization source is
selected by syncsel_NCO(3:0) in config31. The frequency word in the phaseaddAB(31:0) and phaseaddCD(31:0)
registers is added to the accumulators every clock cycle, f
DAC
. The output frequency of the NCO is:
(1)
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