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Groups > sci.electronics.design > #518587
| Newsgroups | sci.electronics.design |
|---|---|
| Subject | Re: really fast buffers |
| From | Steve Wilson <no@spam.com> |
| References | (10 earlier) <787c7a2b-c1a9-4330-830b-8ab9a58d30d0@googlegroups.com> <XnsA972E4A74F46Cidtokenpost@69.16.179.22> <ApmdnWalI5KUniTGnZ2dnUU7-V2dnZ2d@supernews.com> <XnsA9739931E279Aidtokenpost@69.16.179.22> <g1sjm5Ffa4qU1@mid.individual.net> |
| Message-ID | <XnsA973AD4CC2A18idtokenpost@69.16.179.23> (permalink) |
| Organization | http://www.NewsDemon.com |
| Date | 2018-10-06 21:02 +0000 |
Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> wrote:
> Am 06.10.2018 um 21:03 schrieb Steve Wilson:
>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>> On 10/5/18 10:28 PM, 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.
>>> The key ingredient is negative input resistance.
>> That term always bothered me. Negative input resistance to what? If you
>> look a the base input impedance, it is always positive. When the
>> oscillations get going, the transistor is cut off most of the time.
>> Where is the negative input impedance then?
> Negative input impedance from base/gate to GND. It is not positive and
> it sustains the oscillation. And it can be measured.
> https://www.flickr.com/photos/137684711@N07/34701106245/in/album-72157682
> 404684680/
> This is S11 of a baseband amplifier with absurdly high gm to enforce
> low voltage noise with IF3602 JFETs. Everything that is outside the
> circle that goes through X=0 has a negative real part of the input
> impedance. The exact values at the 3 cursors are given in the picture.
> The green line is outside of that circle for most of the intended
> frequency range, until the amplifier runs out of steam.
> BTW I have found no way to cure that without compensating it with a
> positive resistance in the input or cutting the feedback. None of this
> is attractive in a low noise measurement amplifier. :-( :-( :-(
> Those network analyzers are so unforgiving. If you just ignore it,
> you can happily measure around in circuits that have enough source
> resistance. Just sometimes, it won't work. There are lots of
> low noise amplifiers that share its fate.
> BTW, I have built a variation of Winfield's 70 pV/rtHz amplifier from
> AOE3. The non-differential version, since my source is never centered
> around 0 Vdc. Works as promised. :-)
> Yes, it could use even more 'lytics, but that was a test balloon for
> a chopper amplifier. At 500 KHz the caps are no more that critical.
> https://www.flickr.com/photos/137684711@N07/45141749941/in/album-72157662
> 535945536/
> cheers,
> Gerhard
Gerhard, I have the utmost appreciation for your accomplishements and your
skill in electronics.
However, a simple Colpitts oscillator in LTspice shows the input impedance
at the base is positive. The emitter current is also in phase with the base
current.
Another example is a simple 74HC04 Pierce oscillator with an LC tank as
feedback.
The input impedance of the 74HC04 is capacitive. The impedance is
Xc = 1 / (2piFC)
There is no negative input resistance.
A further example is "A General Theory of Phase Noise in Electrical
Oscillators, by Ali Hajimiri, Student Member, IEEE, and Thomas H. Lee,
Member, IEEE"
https://authors.library.caltech.edu/4917/1/HAJieeejssc98.pdf
"Consider as one example the Colpitts oscillator of Fig. 5(a).
The collector voltage and the collector current of the transistor
are shown in Fig. 13. Note that the collector current consists
of a short period of large current followed by a quiet interval.
The surge of current occurs at the minimum of the voltage
across the tank where the ISF is small."
Clearly the collector current is a function of the base current, and is in
phase with the base current. The input impedance at the base is positive,
therefore there is no negative resistance term available.
Oscillators work on positive feedback. If the loop gain is positive and in
phase, oscillations ensue.
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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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