[SI-LIST] Re: Measuring high speed signals
- From: "Ingraham, Andrew" <Andrew.Ingraham@xxxxxxxxxx>
- To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 12 Jun 2001 08:28:33 -0400
> One suggestion would be to use the 50 ohm coax/SMA, but to build it with a
> 10 to 20dB pad very close to the connection point. One of the
> MiniCircuits
> devices or hand built might work. You still have to account for 50 ohms
> to
> ground at the attachment point, but the rest of the scope system should
> have
> limited effect.
Instead of a 50 ohm attenuator, you can do pretty well with just a ~1kohm
(or thereabouts) series resistor in the tip of a 50 ohm probe. This is
probably what the Teradyne papers are referring to.
A 950 ohm series resistor in conjunction with the scope's 50 ohm input,
yields a 20:1 attenuation, very wide bandwidth, and reasonable loading, less
severe than 50 ohms. Not as negligible as a 10 Meg probe at low
frequencies, but probably better at RF where the hi-Z probe's capacitance
and loss components may be significant.
Drs. Johnson and Graham's book "High-Speed Digital Design" has examples in
Chapter 3. Doug Smith's webpage (www.dsmith.org) has something similar, but
with an additional 50 ohm resistor and with frequency compensation added to
flatten the response.
Regards,
Andy
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List archives are viewable at: //www.freelists.org/archives/si-list
Old list archives are viewable at: http://www.qsl.net/wb6tpu
Other related posts:
