DAC5682Z Datasheet, PDF (49/56 Pages) Texas Instruments – 16-BIT, 1.0 GSPS 2x-4x INTERPOLATING DUAL-CHANNEL DIGITAL-TO-ANALOG CONVERTER (DAC)

DAC5682Z
www.ti.com
SLLS853A – AUGUST 2007 – REVISED NOVEMBER 2007
APPLICATIONS EXAMPLES (continued)
DUAL CHANNEL REAL IF OUTPUT RADIO
Refer to Figure 50 for an example Dual Channel Real IF Output Radio. The DAC5682Z receives an interleaved
A/B input data stream and increases the sample rate through interpolation by a factor of 2 or 4. By performing
digital interpolation on the input data, undesired images of the original signal can be push out of the band of
interest and more easily suppressed with analog filters. Real mixing is available at each stage of interpolation
using the CMIX0 and CMIX1 blocks to up-convert the signal. (See Dual-Channel Real Upconversion section)
Both DAC output signals would typically be terminated with a transformer (see the Analog Current Output
section). An IF filter, either LC or SAW, is used to suppress the DAC Nyquist zone images and other spurious
signals before being mixed to RF with a mixer. The TRF3671 Frequency Synthesizer, with integrated VCO, may
be used to drive a common LO input of the mixers for frequencies between 375 and 2380 MHz. Alternatively, two
separate TRF3761 synthesizers could be used for independent final RF frequency placement.
FPGA
Interleaved
A/B Data
D15P/N 100
I
D0P/N
100
Q
SYNCP/N 100
DCLKP/N
100
DAC5682Z DAC
DAC-A
DAC-B
3.3V
3.3V
3.3V
3.3V
3.3V
DLL
opt.
3.3V
PLL
RF
Processing
RF
Processing
PLL/
DLL
100
250 MHz
1000 MHz
Loop
Filter
÷4
÷1
Clock Divider /
Distribution
PLL
CDCM7005
Note : For clarity, only signal paths are shown.
VCXO
Loop
Filter
10 MHz
OSC
375 MHz Min to 2380 MHz Max
(Depends on divider and
“dash #” of TRF3761)
N-
Divider
Div
1/2/4
VCO
PFD
R-
Div
TRF3761-X PLL/VCO
VCTRL_IN
Loop
Filter
CPOUT
Figure 50. System Diagram of a Dual Channel Real IF Output Radio
DIRECT CONVERSION RADIO
Refer to Figure 51 for an example Direct Conversion Radio. The DAC5682Z receives an interleaved complex I/Q
baseband input data stream and increases the sample rate through interpolation by a factor of 2 or 4. By
performing digital interpolation on the input data, undesired images of the original signal can be push out of the
band of interest and more easily suppressed with analog filters.
For a Zero IF (ZIF) frequency plan, complex mixing of the baseband signal is not required. Alternatively, for a
Complex IF frequency plan the input data can be placed at an pre-placed at an IF within the bandwidth
limitations of the interpolation filters. In addition, complex mixing is available at each stage of interpolation using
the CMIX0 and CMIX1 blocks to up-convert the signal to a frequency placement at a multiples ±Fdac/8 or
±Fdac/4. The output of both DAC channels is used to produce a Hilbert transform pair and can be expressed as:
A(t) = I(t)cos(ω_ct) – Q(t)sin(ω_ct) m(t)
(3)
A(t) = I(t)cos(ω_ct) – Q(t)sin(ω_ct) m_h(t)
(4)
where m(t) and mh(t) connote a Hilbert transform pair and ωc is the sum of the CMIX0 and CMIX1 frequencies.
The complex output is input to an analog quadrature modulator (AQM) such as the Texas Instruments
TRF3703-33 for a single side-band (SSB) up conversion to RF. A passive (resistor only) interface to the AQM is
recommended, with an optional LC filter network. The TRF3671 Frequency Synthesizer with integrated VCO may
be used to drive the LO input of the TRF3703-33 for frequencies between 375 and 2380 MHz. Upper
single-sideband upconversion is achieved at the output of the analog quadrature modulator, whose output is
expressed as:
Copyright © 2007, Texas Instruments Incorporated
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