AD9280: 40MSPs

Document created by analog-archivist Employee on Feb 23, 2016
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We design a card with the following parameters:
- Input: analogue VGA (RGB+HSync, VSync)
- Output: Digital (1 or 2 bits color depth) for mono low resolution LCD.

We use your product AD9280 at sampling rate 40MHz, but we use only 1 or 2 MSB
bits (not all 8 bits) I know your product is designed for 32MSPS but it isn't
enough for us. Please confirm if your product should work correctly using 40MHz
if the LSB bits are not important.

If this way isn't good (AD9280 isn't stable at 40MHz) then please offer a
suitable AD converter. (40MHz, only 1-2 MSB used, And the major point is the
Bottom conversion reference should be near AGND)


As you are aware, the AD9280 is only guaranteed to operate up to 32MSPS, so we
cannot and will not give any guarantee that the part will operate at 40MSPS.

Having said that, the datasheet does give the possibility that the device may
be used at 40MSPS. Figure 8 (THD vs clock frequency) and figure 10 (power
consumption vs clock frequency) on page 7, both show data taken at 40MSPS.

Also, the section on "Clock Input" on page 15 mentions that operation is
possible at sample rates higher than 32MSPS with reduced performance.

So it is likely but not guaranteed that the AD9280 will function at 40MSPS. In
other words, most of the AD9280s from different batches that you buy will work
at 40MSPS most of the time under most conditions. In order to ensure that each
and every system you produce will function at 40MSPS, you either need to test
it yourselves in production (and be ready to rework any boards where the
component isn't functional at 40MSPS under worst case conditions) or select
another converter or comparator which is guaranteed to operate at 40MSPS.

AD9283 has versions at 50MSPS, 80MSPS and 100MSPS.

If you need a clamp on the front end, and are using several channels, ADV7202
is a purpose built video ADC/DAC running up to 54MHz.