DAC3484 Datasheet, PDF (56/82 Pages) Texas Instruments – Quad-Channel, 16-Bit, 1.25 GSPS Digital-to-Analog Converter (DAC)

DAC3484
SLAS749A – MARCH 2011 – REVISED JULY 2011
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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 71.
I Data In
16
16
16
16
I Data Out
(A)
Q Data In
16
Fs/2
Mixer
16
±Fs/4
Mixer
Complex
(A)
Signal
16
Multiplier
16
Q Data Out
(B)
(B)
CMIX<1>
sine
CMIX<2> CMIX<0>
16
cosine
16
CMIX<3>
sine
cosine sine
cosine
16
16
16
16
NCO_ENA
(AB)
Numerically
Controlled
Oscillator
Fixed Fs/8
Oscillator
Figure 71. Path of Complex Signal Mixer
B0471-02
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 72.
32
Frequency
Register
32
Σ
32
Accumulator _{32 16}
16
Σ
CLK RESET
16
Look-Up
Table
16
sin
16
cos
f_DAC
NCO SYNC
via
syncsel_NCO[3:0]
Phase
Register
Figure 72. NCO Block Diagram
B0026-03
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:
f_NCO
=
freq ´ f_{NCO _ CLK}
2³²
(1)
56
Copyright © 2011, Texas Instruments Incorporated