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Visitor rafi_11
Visitor
5,236 Views
Registered: ‎06-27-2011

VIRTEX 5 clamping diodes switching time

Hello,

I would like to know how fast are the clamping diodes of the VIRTEX5's IOs.

Can I rely on the diodes to clamp overshoot/undershoot pulses with a width of about 1ns?

 

Thanks

Rafi

 

 

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3 Replies
Scholar austin
Scholar
5,232 Views
Registered: ‎02-27-2008

Re: VIRTEX 5 clamping diodes switching time

r,

 

The diodes are intrinsic to the CMOD fet output transistors:  they are as fast as the transistors themselves.

 

The IBIS files should be used to evaluate the transeint response.

 

All IO designs should be done such that the signal integrity ois as good as possible.  Under- and over- shoot causes  more system jitter, and may affect the reliability of the IO (if it exceeds the ABS MAX ratings).

 

The dynamic clamping behavior is very complex, and best modeled using a signal integrity tool with the IBIS files.  I use Hyperlynx, but there are other tools out there that are good to use as well.  I have seen excursions of greater than 1 volt, + or -, in 1 ns at the IO pin.  It isn't just the diode, it is the series transmission line effects in the package, interacting with the output devices.

 

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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Teacher eteam00
Teacher
5,231 Views
Registered: ‎07-21-2009

Re: VIRTEX 5 clamping diodes switching time

I would like to know how fast are the clamping diodes of the VIRTEX5's IOs.

Can I rely on the diodes to clamp overshoot/undershoot pulses with a width of about 1ns?

 

There are two consideration:

  • using the internal clamp diodes to clamp the external signal to a certain voltage
  • the power dissipation in the clamp diodes which limits the survivable duration and extent/degree of clamping

If you are interested in using the clamp diodes for external voltage limiting purposes, you should use external clamp diodes or follow Austin Lesea's advice with respect to circuit simulation.

 

If you are interested in permitted overshoot conditions, this information is in the Virtex-5 datasheet, DS202 Table 2, and also consult the V-5 User Guide UG190 sections which cover overshoot/undershoot..

 

-- Bob Elkind

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Highlighted
4,216 Views
Registered: ‎10-20-2013

Re: VIRTEX 5 clamping diodes switching time

hey guys

i need .hyp file of virtex 5 fpga board for my final year project. i will be very thankful to you!!

thanx

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