[SI-LIST] Re: PCIe Oscilloscope
- From: Doug Smith <doug@xxxxxxxxxx>
- To: weirsi@xxxxxxxxxx
- Date: Wed, 29 Aug 2007 04:38:17 -0700
Hi Steve, Steve, and the group,
One comment on in-line terminators caught my eye. Even if you had a
GHz of scope bandwidth, use of an external 50 Ohm terminator on the
scope 1 MOhm input limits bandwidth to about 200 MHz and causes you to
see a rising or falling edge twice. At the round trip cable delay
after an edge you will see the reflection at the scope input due to
capacitance (that is not present in a real 50 Ohm input) as an
opposite going spike. A typical scope input capacitance in the 1 MOhm
mode is about 15 pF which gives about a 200 MHz rolloff corner with 50
Ohms.
Doug
steve weir wrote:
> Steve most of the PC USB scopes I have seen have pretty low bandwidths
> and/or sampling rates that tend to top out around 200MHz and 200Msps.
> The software has gotten steadily better, and they usually have the
> advantage of comparatively deep memories. If you are only looking at
> repetitive signals, some of them will do ERTS to get equivalent sample
> rates up to a few Gsps. Otherwise don't expect real time analog b/w
> over 100MHz. If you really need 200MHz I would get one of the current
> generation Tek or Agilent scopes that are quite compact and really go up
> to 1GHz. They pack very nicely into Pelican rolling luggage and have
> USB interfaces for control and capture from your laptop.
>
> Steve
> Steven Kan wrote:
>
>>Heh. I thought he was asking about a PC-based 'scope :)
>>
>>On that note, does anyone here have experience with USB-based oscilloscopes?
>>I am looking for something to use for customer demos of our systems, and
>>would prefer not to have to lug a full-fledged scope around. Luggage is a
>>step-function, and right now I'm very nearly full.
>>
>>I need only two channels + trigger, and really need only about ~200 MHz
>>analog bw. 50 Ohm termination would be nice, but I can get by with an inline
>>terminator if I need to. I don't need much in the way of features and
>>smarts; I just need to display waveforms without horrible lag.
>>
>>I've read various reviews for PC-based 'scopes, but I'd like some feedback
>>from real engineers who have actually used any of these.
>>
>>Any recommendations or contra-recommendations? Thanks!
>>--
>>Steven Kan (p) 310-515-5330 x24
>>Pulse Instruments (f) 310-515-0068
>>1234 Francisco St., Torrance, CA 90502 (c) 818-620-3062
>>mailto:steven@xxxxxxxxxxxxxxxxxxxx
>>http://www.pulseinstruments.com
>>See our new Data Acquisition system!
>>
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>
>
>
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