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DAC5687 EVM Operational Procedure
This tone is being generated by the DAC5687 NCO. With no input data provided to connectors J13
and J14, the Channel A and B data bus inputs will all be zeros, or a full scale negative value in the
default offset binary format. In the X4L mode, after the first 2x interpolation, the full scale DC input
signal at a clock rate of 250 MSPS is mixed with the NCO running at the setting of F
(343597383) to generate a tone at 20 MHz. After a second 2x interpolation, a 20 MHz tone is output
from the DAC sampling at 500 MSPS. The output spectrum should be similar to
Figure 3. Spectrum with CLK2 = 500 MHz, X4L Interpolation and NCO Frequency = 343597383
5. Change the Mode to 1000 F
the output by F
6. Changing the NCO DDS to 3951369913 (2
- 20 MHz = 105 MHz.
7. Change the interpolation to X4, and the mode to No Mixing, the NCO DDC to 286331153 (F
and reduce the CLK2 frequency to < 320 MSPS. The GUI should look as shown in
is now running at the DAC update rate (= CLK2). For CLK2 = 300 MSPS, the result is an output tone
at 20 MHz.
12
DAC5687 EVM
/4 (+,+), corresponding to F
DAC
/4 to 20 MHz + 125 MHz = 145 MHz.
DAC
/4 (see data sheet). This will increase
DAC
32
x (1-20/250)) will now result in an output tone at 125 MHz
SLWU017B – APRIL 2005 – Revised March 2007
www.ti.com
/12.5
NCO
Figure
3.
/15)
NCO
Figure
4. The NCO
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