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AD9648 View Datasheet(PDF) - Analog Devices

Part NameDescriptionManufacturer
AD9648 14-Bit, 125 MSPS/105 MSPS, 1.8 V Dual Analog-to-Digital Converter ADI
Analog Devices ADI
AD9648 Datasheet PDF : 44 Pages
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The AD9648 includes a built-in test feature designed to enable
verification of the integrity of each channel, as well as to
facilitate board level debugging. A built-in self-test (BIST) feature
that verifies the integrity of the digital datapath of the AD9648
is included. Various output test options are also provided to place
predictable values on the outputs of the AD9648.
The output test options are described in Table 18 at Address 0x0D.
When an output test mode is enabled, the analog section of the
ADC is disconnected from the digital back-end blocks and the
test pattern is run through the output formatting block. Some of
the test patterns are subject to output formatting, and some are
not. The PN generators from the PN sequence tests can be reset
by setting Bit 4 or Bit 5 of Register 0x0D. These tests can be
The BIST is a thorough test of the digital portion of the selected
AD9648 signal path. Perform the BIST test after a reset to ensure
performed with or without an analog signal (if present, the
analog signal is ignored), but they do require an encode clock.
the part is in a known state. During BIST, data from an internal
pseudorandom noise (PN) source is driven through the digital
datapath of both channels, starting at the ADC block output. At
the datapath output, CRC logic calculates a signature from the
For more information, see the AN-877 Application Note,
Interfacing to High Speed ADCs via SPI.
data. The BIST sequence runs for 512 cycles and then stops.
Once completed, the BIST compares the signature results with a
predetermined value. If the signatures match, the BIST sets Bit 0
of Register 0x24, signifying the test passed. If the BIST test fails,
Bit 0 of Register 0x24 is cleared. The outputs are connected
during this test, so the PN sequence can be observed as it runs.
Writing the value 0x05 to Register 0x0E runs the BIST. This enables
Bit 0 (BIST enable) of Register 0x0E and resets the PN sequence
generator, Bit 2 (initialize BIST sequence) of Register 0x0E. At the
completion of the BIST, Bit 0 of Register 0x24 is automatically
cleared. The PN sequence can be continued from its last value
by writing a 0 in Bit 2 of Register 0x0E. However, if the PN
sequence is not reset, the signature calculation does not equal
the predetermined value at the end of the test. At that point, the
user needs to rely on verifying the output data.
Rev. 0 | Page 32 of 44
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