Posted: Mon Jun 13, 2011 5:43 am Post subject: External Clocking Specifications
The X6-400M looks like a very nice card and we have a few questions about the external clocking.
Our application requires external clocking of the A/D converters at a non-fixed frequency (A/D clock frequency varies with time) and non-fixed peak-to-peak amplitude (p-p voltage varies with time).
Using the previous generation X5-400M, we were able to achieve very good clocking performance over the required voltage and frequency range. The X5-400M uses the ICS8533 Clock Buffer chip.
However, we have experimentally found with the help of Innovative Tech Support that our X5-G12 cards require a voltage of about 2V-3.3V peak-to-peak to externally clock, which agrees with cards tested at the factory. This reduced voltage range (less than a factor of 2 in range) requires that we use an additional high frequency circuitry to condition and amplify the clock. The X5-G12 uses the CDCE72010 Clock Buffer chip.
We noticed that the X6-400M also uses the CDCE72010 Clock Buffer chip and were concerned about the specifics of the clocking performance.
Does the X6-400M hit the specified clock input voltage range of 0.1-3.3V peak-to-peak as listed in the data sheet (i.e. uses different circuit than the X5-G12)?
Table 16. External Clock Input Requirements in the X6-400M user manual lists a 0.15 - 1.3V peak-to-peak external clock input. This looks different than the data sheet, which lists 0.1-3.3V peak-to-peak. Could you help us to understand the difference between these two specs?
Thank you very much. We are looking forwards to trying this card.
Although the X6-400M clock system is based on the CDCE72010, it does not use the same input interface at the external clock connector as the X5-G12. A TI CDCLVP1204 sits between the 72010 and the clock connector and is used to steer the external clock to either the 72010 reference or aux inputs as needed by the operating mode of the board.
The datasheet values for the input range are correct. The input sensitivity of the 1204 is specified as 0.1Vp-p, which is where the datasheet low value originates. We have tested the external input at 0 dBm but we do not have test data at the 0.1 Vp-p point. The 3.3Vp-p max specification is due to the power supply used to power the 1204 device. The 1204 input could be damaged if this voltage is exceeded.
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