HSC-ADC-FIFO5-INTZ Analog Devices Inc, HSC-ADC-FIFO5-INTZ Datasheet - Page 24

• Manufacturer Part Number: HSC-ADC-FIFO5-INTZ
• Description: Interposer Quad/octal ADCs
• Manufacturer: Analog Devices Inc

Specifications of HSC-ADC-FIFO5-INTZ

• Accessory Type: ADC Interface Board
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: AD6640
• Lead Free Status / Rohs Status: Supplier Unconfirmed

HSC-ADC-EVALA-SC/HSC-ADC-EVALA-DC
FFT NOISE FLOOR HIGHER THAN EXPECTED
Scenario: The noise floor of the FFT is higher than expected.
Note that a higher than expected noise floor on the FFT can
often be traced back to timing issues in the clock path.
1
2
3
4
Put a very slow sine wave signal into the ADC (such as 0.1
MHz to 1 MHz) and initiate a time-domain plot. If the plot
looks similar to Figure 21, there are timing issues.
Switch Jumpers J304 and/or J305 to their alternate
positions to invert the clock.
The four XOR gates of U302 can be used to insert delay
into the high speed clock path or to invert the clock to
optimize timing. Try moving jumpers J314 and J315 to
their alternate position. This should allow enough
flexibility for you to adjust timing under any conditions.
To gain even finer adjustments, use the installed trim pot,
R312 and R315. To undo the default bypass, the solder
jumpers J310-J313 must be removed first.
Figure 21. Example of How Timing Issues Affect the Noise Floor
Figure 20. Incorrect Setting for Twos Complement
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LARGE SPUR IN FFT (IMAGE PROBLEM)
Scenario: There is a large spur in the FFT (image of the
fundamental) when evaluating the demultiplexed outputs (such
as the AD9430).
1.
2.
Click Config > Channel Select, opening the window shown
in Figure 23Double-check and make sure the Interleaved
Data box is selected. Click OK. Note that Channel A in the
software corresponds to Channel 1 on the FIFO schematics
and the bottom FIFO on the evaluation board. Channel B
corresponds to Channel 2 on the FIFO schematics and the
top FIFO on the evaluation board (closest to the Analog
Devices logo). See the Jumpers section for more
information.
The interleaved priority menu shows either Channel A or
Channel B checked.
Figure 22. AD9430 Timing Issue
Figure 23. Channel Selection