Datasheet

DAC-A
DAC-B
Q-FIR1
CMIX1
I-FIR1
CMIX0
Q-FIR0
I-FIR0
FIFO & Demux
100
100
100
CLKIN/C
opt.
PLL
Loop
Filter
DLL
DAC5682ZDAC
100
FPGA
PLL
÷1÷4
ClockDivider /
Distribution
CDCM7005
100
250 MHz
1000 MHz
PLL/
DLL
VCO
N-
Divider
R-
Div
PFD
CPOUT
VCTRL_IN
90
0
TRF3703-33 AQM
TRF3761-XPLL/VCO
Loop
Filter
Div
1/2/4
375 MHzMinto 2380 MHzMax
(Dependsondividerand
“dash #” ofTRF3761)
10 MHz
OSC
RFOUT
Note: Forclarity, onlysignalpathsareshown .
Optional (100 ohm)
Filter Network
LVDS Data Interface
Loop
Filter
VCXO
I
Q
GC5016 or GC5316 DUC,
With GC115 CFR and/or
DPD Processor
5V
115
634
115
634
115 115
634 634
100
DCLKP/N
SYNCP/N
D0P/N
D15P/N
Interleaved
I/QData
DAC5682Z
SLLS853E –AUGUST 2007–REVISED AUGUST 2012 www.ti.com
APPLICATIONS EXAMPLES (continued)
RF(t) = I(t)cos(ω
c
+ ω
LO
)t – Q(t)sin(ω
c
+ ω
LO
)t (5) (5)
Flexibility is provided to the user by allowing for the selection of negative CMIX mixing sequences to produce a
lower-sideband upconversion. Note that the process of complex mixing translates the signal frequency from 0 Hz
means that the analog quadrature modulator IQ imbalance produces a sideband that falls outside the signal of
interest. DC offset error in DAC and AQM signal path may produce LO feed-through at the RF output which may
fall in the band of interest. To suppress the LO feed-through, the DAC5682Z provides a digital offset correction
capability for both DAC-A and DAC-B paths. (See DAC_offset_ena bit in CONFIG3.)
The complex IF architecture has several advantages over the real IF architecture:
• Uncalibrated side-band suppression ~ 35 dBc compared to 0 dBc for real IF architecture.
• Direct DAC to AQM interface – no amplifiers required
• Nonharmonic clock-related spurious signals fall out-of-band
• DAC 2nd Nyquist zone image is offset f
DAC
compared with f
DAC
– 2 × IF for a real IF architecture, reducing the
need for filtering at the DAC output.
• Uncalibrated LO feed through for AQM is ~ 35 dBc and calibration can reduce or completely remove the LO
feed through.
Figure 51. System Diagram of Direct Conversion Radio
CMTS/VOD TRANSMITTER
The exceptional SNR of the DAC5682Z enables a dual-cable modem termination system (CMTS) or video on
demand (VOD) QAM transmitter in excess of the stringent DOCSIS specification, with >74 dBc and 75 dBc in the
adjacent and alternate channels.
Refer to Figure 50 for an example Dual Channel Real IF Output Radio – this signal chain is nearly identical to a
typical system using the DAC5682Z for a cost optimized dual channel two QAM transmitter. A GC5016 would
take four separate symbol rate inputs and provide pulse shaping and interpolation to ~ 128 MSPS. The four QAM
carriers would be combined into two groups of two QAM carriers with intermediate frequencies of approximately
30 MHz to 40 MHz. The GC5016 would output two real data streams to one DAC5682Z through an FPGA for
CMOS to LVDS translation. The DAC5682Z would function as a dual-channel device and provide 2x or 4x
interpolation to increase the frequency of the 2nd Nyquist zone image. The two signals are then output through
the two DAC outputs, through a transformer and to an RF upconverter.
50 Submit Documentation Feedback Copyright © 2007–2012, Texas Instruments Incorporated
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