Lpc2000

Hello Dave,

> 
> I don't think the scope is influencing things significantly as I've 
> observed faster & better quality waveforms. However I'm keen to try 
> the coax connector & divider trick you described. I'm not 100% clear 
> of the configuration though. Could you talk me through the setup ?
> 

There are several nice instruction sets on the web, like this more
elaborate probe:
http://www.emcesd.com/1ghzprob.htm

I usually forego the resistor to GND and the caps since a well
terminated coax provides a 50ohm load just by itself. This seems to be
what Maxim described in one of their app notes:
http://www.maxim-ic.com/appnotes.cfm/appnote_number/3699

The simplest "probe" would just contain one 450ohm SMT resistor, or
453ohms since that is the closest value you can find in the usual 1%
category. It must be a low-inductance resistor which most of them are
nowadays. When you solder that in series with the center conductor of
a coax you have a 1:10 divider, assuming 50ohm coax which is properly
terminated at the scope. Use a small SMT cap in series if you want to
avoid any DC draw. Make it as neat as you can and as short as practical.

Very important is a short connection to ground. Below 100MHz you can
get away with 1/2".

Then place a jar on the counter where people can "donate" a girl scout
cookie or something delicious. Because everyone in the lab will want
to borrow your new probe at some point.

Regards, Joerg

http://www.analogconsultants.com/