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Re: really fast buffers

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On Friday, October 5, 2018 at 10:28:43 PM UTC-4, Steve Wilson wrote:
> George Herold <gherold@teachspin.com> wrote:
> 
> > It oscillates because of a slow edge and no hysteresis? 
> 
> It oscillates because of inductance in the base lead. Along with the base-
> emitter capacitance and capacitance from the emitter to ground, this forms 
> a Colpitts oscillator, which is one of the most vigorous oscillators known. 
> It can accept an extremely wide range of parameters and still oscillate.
> 
> The purpose of the resistor in the base lead is to dampen the Q of the tank 
> so oscillations are no longer possible.
>  
> > Is it similar to cap. multiplier oscillations?  
> 
> Could be. Any place where you have some inductance in the base and 
> capacitance from the emitter to ground could form a Colpitts, especially 
> where you have some inductance in the emitter lead.
My first (or second) cap multiplier oscillated and I added a F-bead and 
100 ohm resistor on the base lead, through hole hair-pin.  
No problems since then.    

George H. 
> 
> Other configurations where fast transistors are connected together could 
> become an oscillator. Some examples are:
> 
>   Cascode
>   Darlington
>   Sziklai pair
>   etc
> 
> > (do all single transistor circuits map onto each other?)
> 
> The various configurations of the Colpitts are basically the same. It's 
> just where you put the ground that makes them look different.
> 
> The difficulty with the Colpitts is it loves to oscillate. The conditions 
> are layout-dependent and dependent on the gain and bandwidth of the 
> transistor. The oscillations can completely destroy the desired performance 
> of the circuit.
> 
> My approach is to assume the circuit will oscillate under the right 
> conditions, and to include a resistor in the base in all critical circuits 
> that could be susceptible to parasitics. After a while, you get to know 
> what value would be appropriate, usually from 5 to 50 ohms. But check 
> carefully.
> 
> This creates a problem. Often the oscillation frequency is far above the 
> frequency range of the best equipment available in your lab. To compensate, 
> you need some way to perturb the circuit and look for any change in the 
> operating parameters. One method is to use a dental pick which is available 
> at most pharmacies. This is a small stainless hook imbedded in plastic, 
> with a cover to fit over the top. You can touch various points in the 
> circuit an see if you can detect any change in the operataion.
> 
> The best by far is a wideband spectrum analyzer. You can make a small loop 
> feeding a coax cable to the analyzer. Bring the loop near the circuit. any 
> oscillation should become visible in the display.
> 
> Of course, with modern transistors, especially SiGe, you need a very high 
> frequecy specctrum analyzer. These are not cheap.
>  
> > George H.

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really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-03 15:03 -0700
  Re: really fast buffers Lasse Langwadt Christensen <langwadt@fonz.dk> - 2018-10-03 15:23 -0700
    Re: really fast buffers Andy Bennet <andyb@andy.com> - 2018-10-04 08:20 +0100
      Re: really fast buffers Lasse Langwadt Christensen <langwadt@fonz.dk> - 2018-10-04 08:45 -0700
  Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-03 15:52 -0700
    Re: really fast buffers George Herold <gherold@teachspin.com> - 2018-10-03 18:08 -0700
      Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-03 20:02 -0700
  Re: really fast buffers bitrex <user@example.net> - 2018-10-03 21:54 -0400
    Re: really fast buffers Steve Wilson <9fe142ac@gmail.com> - 2018-10-03 20:10 -0700
      Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-03 20:40 -0700
        Re: really fast buffers pcdhobbs@gmail.com - 2018-10-04 05:00 -0700
          Re: really fast buffers Steve Wilson <9fe142ac@gmail.com> - 2018-10-04 08:39 -0700
            Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-04 12:38 -0400
              Re: really fast buffers Steve Wilson <9fe142ac@gmail.com> - 2018-10-04 14:35 -0700
                Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-04 18:27 -0400
                Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-05 03:21 +0000
                Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-05 10:38 -0400
            Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-04 11:50 -0700
              Re: really fast buffers Clifford Heath <no.spam@please.net> - 2018-10-05 09:26 +1000
                Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-04 17:09 -0700
                Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-05 03:12 +0000
                Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-05 14:18 -0700
                Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-05 23:42 +0000
                Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-06 14:41 -0400
              Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-05 03:09 +0000
                Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-05 10:40 -0400
                Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-05 11:06 -0400
                Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-05 19:16 -0700
                Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-05 14:26 -0700
                Re: really fast buffers George Herold <gherold@teachspin.com> - 2018-10-05 18:36 -0700
                Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-05 19:22 -0700
                Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-06 02:28 +0000
                Re: really fast buffers <698839253X6D445TD@nospam.org> - 2018-10-06 06:03 +0000
                Re: really fast buffers Steve Wilson <9fe142ac@gmail.com> - 2018-10-05 23:41 -0700
                Re: really fast buffers <698839253X6D445TD@nospam.org> - 2018-10-06 08:12 +0000
                Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-06 14:46 -0400
                Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-06 19:03 +0000
                Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-06 15:32 -0400
                Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-06 20:08 +0000
                Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-06 22:19 +0200
                Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-06 21:02 +0000
                Re: really fast buffers tabbypurr@gmail.com - 2018-10-06 16:57 -0700
                Re: really fast buffers krw@notreal.com - 2018-10-06 22:30 -0400
                Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-07 04:30 +0200
                Re: really fast buffers <698839253X6D445TD@nospam.org> - 2018-10-07 07:15 +0000
                Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-07 08:24 -0700
                Re: really fast buffers bill.sloman@ieee.org - 2018-10-07 18:51 -0700
                Re: really fast buffers tabbypurr@gmail.com - 2018-10-08 08:16 -0700
                Re: really fast buffers Winfield Hill <hill@rowland.harvard.edu> - 2018-10-07 07:19 -0700
                Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-10 00:38 -0700
                Re: really fast buffers tabbypurr@gmail.com - 2018-10-10 03:02 -0700
                Re: really fast buffers bill.sloman@ieee.org - 2018-10-10 04:07 -0700
                Re: really fast buffers DecadentLinuxUserNumeroUno@decadence.org - 2018-10-10 11:28 +0000
                Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-11 22:06 -0700
                Re: really fast buffers bill.sloman@ieee.org - 2018-10-12 00:08 -0700
                Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-13 22:29 -0700
                Re: really fast buffers bill.sloman@ieee.org - 2018-10-14 00:30 -0700
                Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-15 19:38 -0700
                Re: really fast buffers bill.sloman@ieee.org - 2018-10-15 20:55 -0700
                Re: really fast buffers tabbypurr@gmail.com - 2018-10-14 04:31 -0700
                Re: really fast buffers bill.sloman@ieee.org - 2018-10-14 07:29 -0700
                Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-15 19:42 -0700
                Re: really fast buffers bill.sloman@ieee.org - 2018-10-15 20:57 -0700
                Re: really fast buffers tabbypurr@gmail.com - 2018-10-16 08:41 -0700
                Re: really fast buffers krw@notreal.com - 2018-10-16 17:38 -0400
                Re: really fast buffers bill.sloman@ieee.org - 2018-10-16 19:37 -0700
                Re: really fast buffers bill.sloman@ieee.org - 2018-10-16 19:40 -0700
                Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-15 19:40 -0700
                Re: really fast buffers Robert Baer <robertbaer@localnet.com> - 2018-10-11 22:04 -0700
                Re: really fast buffers tabbypurr@gmail.com - 2018-10-12 08:02 -0700
                Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-10 14:06 +0200
                Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-10 08:31 -0700
                Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-11 01:49 +0200
                Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-10 17:41 -0700
                Re: really fast buffers "John Miles, KE5FX" <jmiles@gmail.com> - 2018-10-10 20:53 -0700
                Re: really fast buffers Jasen Betts <jasen@xnet.co.nz> - 2018-10-11 05:47 +0000
                Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-11 12:35 +0200
                Re: really fast buffers George Herold <gherold@teachspin.com> - 2018-10-06 12:39 -0700
                Re: really fast buffers Steve Wilson <no@spam.com> - 2018-10-06 20:11 +0000
                Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-08 20:26 -0700
                Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-06 14:45 -0400
                Re: really fast buffers George Herold <gherold@teachspin.com> - 2018-10-06 12:46 -0700
                Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-08 21:00 -0700
                Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-09 07:11 +0200
                Re: really fast buffers Chris Jones <lugnut808@spam.yahoo.com> - 2018-10-09 23:20 +1100
                Re: really fast buffers Jeroen Belleman <jeroen@nospam.please> - 2018-10-09 15:17 +0200
          Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-04 09:18 -0700
            Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-04 12:39 -0400
              Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-04 11:51 -0700
        Re: really fast buffers Piotr Wyderski <peter.pan@neverland.mil> - 2018-10-08 13:19 +0200
          Re: really fast buffers John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-08 08:52 -0700
  Re: really fast buffers whit3rd <whit3rd@gmail.com> - 2018-10-04 11:57 -0700
  Re: really fast buffers David Nadlinger <david@klickverbot.at> - 2018-10-04 23:05 +0100
    Re: really fast buffers John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-04 17:23 -0700
      Re: really fast buffers Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2018-10-05 11:26 +0200
        Re: really fast buffers Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-05 10:44 -0400

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