TEK Scope Probe question

It seemed like a bad omen to me when google acquired DejaNews. FWIW, here's how I search usenet these days:

cd /u/newsarchive/sci/electronics/design find . | xargs grep -l Kuenz | xargs grep LTSpice

Of course, one can append as many greps and regexes as needed.

I am also putting the finishing touches on my own personal, very picky, web crawler. You might say that I've had it with using other people's search engines.

--
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   __/  \ 
  /  \__/ 
  \__/    Don Kuenz 
  /  \__ 
  \__/  \ 
     \__/

I've been away from scope cal since the '70's, but I did design the fast rise output of the PG506. If you expect it to work, you need to terminate it in 50 ohms. As I recall, scope probes were spec'd with a 25 ohm source and a very clean fixture. And the PG506 isn't fast by today's standards...not even close.

As for the .35 relationship, between bandwidth and risetime... I don't think tek scopes were ever gaussian. They had the crap peaked out of them. Then when you have digital samples and apply serious signal processing, that relationship goes out the window.

Interesting! Thanks for that.

I think it was Werner Von Braun who said that "one experiment is worth a thousand expert opinions."

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation

Interesting. I thought they were pretty tight with LeCroy--they did that 100 GHz digitizer together iirc.

Back in the 80s there was a 70 GHz scope based on SQUIDS, made by Hypres, a few miles from me.

Hypres was started by Sadeg Faris, who used to be at IBM Watson. The parlour trick was going from room temperature to 4K along PC traces short enough to preserve the bandwidth--about 2 inches iirc.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

"John Larkin" napisal w wiadomosci news: snipped-for-privacy@4ax.com...

In German is also "Probiren is better than studiren". S*

On Mon, 27 Jan 2014 19:41:38 -0600, amdx wrote:

That's the first time I've seen this in print: "For example, a Tektronix 100MHz probe provides 100MHz performance (-3dB) at the probe tip when used with a compatible oscilloscope".

If, by that, they mean "used with a 100MHz oscilloscope", that's theoretically impossible, unless the probe itself has zero risetime.

There's an older Tek dissertation on probes on BAMA. It's DJVU, if you can't manage that, I can convert it to PDF, and post it to ABSE. IMNSHO, it's better than the later, glossy, thing.

I shall have to extend my proposed measurements to Tek probes, as well as my PMK ones. I think I've still got some Tek 500MHz ones, somewhere.

All I have to do, now is find a way of fitting 1meg/22pF 0802 inside a BNC, as a dummy scope.

I'd like to do 9950+50/22pF, to pick off at 50ohms and use the spectrum analyzer/tracking generator combination. I can get to 1.5 GHz that way. Dunno if that's going to be feasible - yet.

I did a Spice model of a basic probe, eons ago, that demonstrates the effect of resistive cable versus plain coax.

Play with it, plot file is at the end:

Version 4 SHEET 1 880 680 WIRE -48 16 -80 16 WIRE 32 16 16 16 WIRE -80 112 -80 16 WIRE -80 112 -144 112 WIRE -64 112 -80 112 WIRE 32 112 32 16 WIRE 32 112 16 112 WIRE 96 112 32 112 WIRE 240 112 192 112 WIRE 384 112 320 112 WIRE 480 112 384 112 WIRE 96 144 48 144 WIRE 240 144 192 144 WIRE 480 160 480 112 WIRE -144 288 -144 192 WIRE 48 288 48 144 WIRE 48 288 -144 288 WIRE 144 288 48 288 WIRE 240 288 240 144 WIRE 240 288 144 288 WIRE 384 288 384 192 WIRE 384 288 240 288 WIRE 480 288 480 224 WIRE 480 288 384 288 WIRE 144 320 144 288 FLAG 144 320 0 FLAG 480 112 Scope_out IOPIN 480 112 Out SYMBOL ltline 144 128 R0 SYMATTR InstName O1 SYMATTR Value rescable SYMBOL res 368 96 R0 SYMATTR InstName R1 SYMATTR Value 1e6 SYMBOL voltage -144 96 R0 WINDOW 123 24 132 Left 2 WINDOW 39 0 0 Left 2 WINDOW 3 8 159 Left 2 SYMATTR Value2 AC 1 SYMATTR Value PULSE(0 1 1u 10n 10n) SYMATTR InstName V1 SYMBOL res 32 96 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 9e6 SYMBOL cap 464 160 R0 SYMATTR InstName C1 SYMATTR Value 22p SYMBOL cap 16 0 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 12.7p SYMBOL res 224 128 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName RHF SYMATTR Value 100 TEXT 144 360 Left 1 !.model RG223 LTRA (\n+ len=3\n+ L=.077u\n+ C=30.8p\n+ R=1.3e-3\n+) TEXT -144 344 Left 2 !.ac dec 1000 0.1 500meg TEXT -144 328 Left 1 !.opt plotwinsize=0 TEXT 312 360 Left 1 !.model rescable LTRA (\n+ len=3\n+ L=.077u\n+ C=30.8p\n+ R=65\n+) TEXT -144 376 Left 1 !.net I(R1) V1 TEXT 72 184 Left 1 ;Select model rescable or RG223 TEXT 120 72 Left 1 ;3 ft. cable TEXT 264 64 Left 1 ;HF trim TEXT 392 64 Left 2 ;Scope internal R and C. TEXT 16 0 Left 1 ;LF trim TEXT -144 360 Left 2 ;Change to: .tran 0 2u 0 10p for pulse response. RECTANGLE Normal 592 320 352 48 2

[AC Analysis] { Npanes: 3 { traces: 1 {524290,0,"V(scope_out)"} X: ('M',1,10,0,5e+008) Y[0]: (' ',0,0.0223872113856834,1,0.1) Y[1]: (' ',0,-900,90,0) Log: 1 2 0 GridStyle: 1 PltMag: 1 Text: "dB" 1 (23.767107888278,0.075938107586479) ;Vout / Vin }, { traces: 1 {4,0,"1/Re(Yin(V1))"} X: ('M',1,10,0,5e+008) Y[0]: ('_',4,10,0,1e+008) Y[1]: ('m',1,-0.001,0.0002,0.001) Log: 1 1 0 GridStyle: 1 PltMag: 1 Text: "" 1 (70.1369311952015,2253933.90473479) ;Input parallel resistance, ohms. }, { traces: 1 {5,0,"Im(Yin(V1))/w"} X: ('M',1,10,0,5e+008) Y[0]: ('p',1,2.7e-012,9e-013,1.17e-011) Y[1]: ('m',2,-0.001,0.0002,0.001) Log: 1 1 0 GridStyle: 1 PltMag: 1 Text: "" 1 (82.0929937557222,8.43019058214655e-012) ;Input parallel capacitance, farads. } }

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)

They went on blithely quoting it, though.

I've spent countless hours getting the front edge right on supposedly calibrated scopes. They all seem to come with more overshoot than I like to see, which makes the risetime look better than it actually is. Risetime, to me is from 10% to 90% *of the final, settled, "flat" value*, ignoring any overshoot. Some people seem to think otherwise.

I won't have anything to do with Tek digital scopes. My one in-service digital scope is HP/Agilent.

I'm pushing to get an Iwatsu analog on trial.

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)

Yeah. It's called cheating ;-)

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)

Maybe they mean that the combination has 100 MHz 3dB response.

An attenuator probe can have a high-frequency boost curve that can decrease the risetime of a scope, increase its bandwidth a bit. I measured that effect recently.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation

Because you're not getting a flat response.

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)

Or sometimes called "equalizing." Why is it cheating?

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation

Look at the risetimes that I measured with probes. They are essentially identical to the native risetime of the scope. The probes are practically transparent. That looks like good engineering to me.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation

Hyperlabs (Agoston Agoston) was involved, too. It was custom IC shock line stuff. Appeared to be a commercial failure. We contacted them about it, and they said that they'd need a big order to fire up the fab and make any more of them.

That was (nopun) really cool stuff. They sprayed liquid helium on a circuit that was, as I recall, even closer than 2" from the connector.

It was a 1-bit "slideback" sampler, which is slow and has bad statistics; it digitizes the median of a noisy signal, not the average. Tek and Agilent developed 70-80 GHz 2-diode shockline samplers and pretty much killed off scopes that needed helium dewars.

There's not too much point making a 100 or 200 GHz sampling scope; cables and connectors don't work well up there.

My EE senior project was "The Tunnel Diode Slideback Sampler", most of the work (ok, all of the work) being done the night before it was due. I got 50 MHz bandwidth (which is of historical interest) but it worked.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

You can do electrooptic or plasma-optic sampling much faster than that with a femtosecond laser, but of course the circuit has to trigger off the laser rather than the other way round, which is a fairly serious limitation. The electrooptic effect is really quick.

Building and measuring the circuit the night before, I believe. The calculations probably took a bit longer than that.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Ummm, calculations?

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation

You know, the things people used to do with slide rules before they could just poke SPICE. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Heck, the parts values in the sampler were just guessed and wired up. I did tweak some values to get it to work. All I wanted was some scope pictures (remember Polaroid scope cameras?) so I could get the paper done and get some sleep.

The idea was: sum the input signal and a feedback signal into a tunnel diode, through resistors. Also sum in a fast current spike, capacitively coupled from another TD. If the spike flips the sampling TD high, reduce the feedback for the next time; if not, increase it. The feedback is in equal steps, so the slew response is a stairstep.

It would also work in successive approximation, which I noted in my paper.

I won a couple of awards for this and had to present it three times. PITA.

I guess I should have sent it to Tek and applied for a job there. Oregon is nice.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com