DAC3482 Datasheet, PDF (55/79 Pages) Texas Instruments – Dual-Channel, 16-BIT, 1.25 GSPS Digital-to-Analog Converter (DAC)

DAC3482
www.ti.com
SLAS748A – MARCH 2011 – REVISED JUNE 2011
COMPLEX SIGNAL MIXER
The DAC3482 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 70.
16
16
16
16
I Data In
16
Fs/2
Mixer
16
±Fs/4
Mixer
Complex
I Data Out
Signal
16
Multiplier
16
Q Data In
Q Data Out
CMIX<1>
CMIX<2> CMIX<0>
sine
16
sine
cosine
16
16
cosine sine
16
16
CMIX<3>
cosine
16
NCO_ENA
Numerically
Controlled
Oscillator
Fixed Fs/8
Oscillator
Figure 70. Path of Complex Signal Mixer
B0471-01
FULL COMPLEX MIXER
The DAC3482 has a full complex mixer (FMIX) block with a Numerically Controlled Oscillators (NCO) that
enables flexible frequency placement without imposing additional limitations in the signal bandwidth. The NCO
has a 32-bit frequency registers (phaseadd(31:0)) and a 16-bit phase register (phaseoffset(15:0)) that generate
the sine and cosine terms for the complex mixing. The NCO block diagram is shown below in Figure 71.
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 71. 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 phaseadd(31:0) register 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)
Copyright © 2011, Texas Instruments Incorporated
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