generate a square signal with a 3.8 ns "plate"

This appears to require registration. Can you put it somewhere public?

-- Peter

Sorry, try this

Regards RG

Scope schrieb:

Are you sure that you do not succeed? You need more than 1GHz of Scope and probe bandwidth to reliably measure signal slopes in the order of 1ns. (As the frequency is fixed, the plate width is defined by the slope of the signal and the duty cycle)

For example with a 150MHz scope you will see a sine wave, no matter what waveform the FPGA generates.

Kolja Sulimma

My Scope is a Tektronix TDS 3054 500Mhz ( 5 GS/s ). Do you think it is no enough ? Is it possible that I can't see the real signal ?

( However, Shannon's rule about sampling is respected )

Scope schrieb:

And what kind of probe? How attatched?

Regards Falk

My probe is a Tektronix P6139A Voltage probe 500 MHz 8.0 pF 10 Mohms 10x

Scope schrieb:

Way too slow, too much input capacitance. Try to use a passive 50 ohms probe (see link).

Regards Falk

Scope schrieb:

With a perfectly attached 500MHz setup you will see only the one overtone (300MHz) undamped. The 500MHz part will allready be damped. So even if the FPGA would ouput a perfect square wave your scope would see something that looks worse then the K=5 case in that URL:

If you clamp the gnd connection of a regular probe somewhere on your board and just touch the probe to your signal you are going to see something that is a lot worse. Follow the link that Falk suggested and solder a coax cable with a resistor to your signal.

ALSO: If your signal is unterminated it will look really bad. If it is series terminated it will only look good at the receiver.

ALSO: Select fast slew rate and 24mA drive strength for your output.

Kolja Sulimma