John Larkin's LC oscillator
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From: Joel Koltner on 17 Jun 2010 14:52 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in message news:oook169dj13u47dsfb15f6e80vo6adq4u5(a)4ax.com... > But, hey! Ignorant young bucks with no knowledge of basics are good > for business :-) The smart young bucks will demand to keep a copy of your brain after the contract is up. :-)
From: Jim Thompson on 17 Jun 2010 15:01 On Thu, 17 Jun 2010 11:52:43 -0700, "Joel Koltner" <zapwireDASHgroups(a)yahoo.com> wrote: >"Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in >message news:oook169dj13u47dsfb15f6e80vo6adq4u5(a)4ax.com... >> But, hey! Ignorant young bucks with no knowledge of basics are good >> for business :-) > >The smart young bucks will demand to keep a copy of your brain after the >contract is up. :-) All the schools teach anymore is CAD. No one seems to know even the very basic behavior of transistors, or resistors, and even less about energy storage devices such as capacitors and inductors. Sigh :-( ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: Joel Koltner on 17 Jun 2010 16:25 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in message news:s3sk16hinghvri6lirsgiolhinhgmu17iu(a)4ax.com... > All the schools teach anymore is CAD. No one seems to know even the > very basic behavior of transistors, or resistors, and even less about > energy storage devices such as capacitors and inductors. Sigh :-( Well, as I've suggested before, I think there's reasonably good money to be made in giving courses on this stuff. Granted, giving live courses involves travel and finding people willing to pay the average going rate of ~$500/day for professional instruction, but selling DVD at, e.g. $99-$399 works pretty well too. Even books can be OK, although it seems to me that there's rather more grunt work involve with books for each dollar you can charge than with DVDs, and from a student's perspective DVDs allow for a somewhat more hands-on feel anyway. Check out, e.g., http://www.scitechpublishing.com/index.asp?PageAction=VIEWCATS&Category=27 ... $110 for 50 minutes of "Introduction to the Smith Chart?" I doubt the author, Glenn Parker, spent more than a week working on it! ---Joel
From: Phil Hobbs on 17 Jun 2010 17:01 Jim Thompson wrote: > On Thu, 17 Jun 2010 12:58:30 -0400, Phil Hobbs > <pcdhSpamMeSenseless(a)electrooptical.net> wrote: > >> John Larkin wrote: >>> On Thu, 17 Jun 2010 09:44:44 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>> > [snip] >>> The base voltage needs to be +1 jd for the thing to oscillate at >>> equilibrium. The clamp device, c-b junction or schottky, has about the >>> same tc, but in the opposite direction. In the c-b case (with a low >>> secondary swing, not some awful class C thrashing, and a big base cap, >>> so it's not a blocking oscillator) the collector swing that pulls >>> current out of the base capacitor touches zero, near where the >>> transistor saturates. In fact, the tc of the c-b junction is canceling >>> the tc of the e-b junction. Not perfectly, because they are >>> effectively used at different currents. Because of reverse beta, some >>> of the tank energy can be clamped through the emitter, which is a bit >>> negative at that instant. But even that current flow happens when the >>> c-b junction is forward biased. >>> >>> Schottky: suppose we need +0.6 on the base for stable oscillation. The >>> collector will dip down to, say, 0.3, the schottky will conduct and >>> pull charge out of the base cap, and it will stabilize there. The tc's >>> almost cancel. If you assume the amplitude limiting is just brute >>> clamping of the swing, the tc's still cancel. No saturation, since the >>> c-b junction doesn't get forward biased. This assumes you've chosen a >>> suitable base resistor, not jamming too much current into the base, >>> and the transistor has reasonable beta. >>> >>> Actually, the base AGC thing must be happening. With small feedback >>> voltage into the emitter, a sim shows that the transistor is on >>> throughout the cycle, "class A." So Ic ~= beta * Ib, on average. >>> Average Ic would be large if the current through the base resistor >>> were all actually going into the base. But it's not: the base cap is >>> being discharged at the negative swing of the collector, stealing base >>> current and reducing transconductance, and that is exquisitely >>> sensitive to p-p amplitude. Some tank energy does of course get lost >>> to the emitter... both mechanisms are at work. Fortunately, both >>> stabilize the amplitude. >>> >>> In my sim, if you short the tank, the supply current goes up about >>> 30x. (Hmmm, Rb could be bigger!) Output swing is 10.11 volts p-p with >>> a 5-volt supply. >>> >>> Several people have modeled this circuit with small base caps and low >>> transformer ratios and lots of base bias current. That works >>> differently. >>> >>> John >> Interesting, thanks. I agree that the Baker clamp pretty well fixes the >> saturation problem. >> >> Cheers >> >> Phil Hobbs > > Phil, Don't you have means to simulate Larkin's oscillator? > > If you bothered to do that you'd find some of Larkin's statements > above are _absolutely_ incorrect, and others are so hand-waving as to > be hilarious. > > But, hey! Ignorant young bucks with no knowledge of basics are good > for business :-) > > ...Jim Thompson Of course I have. I'm hip deep in measuring very small nonlinearities in InGaAs photodiodes just now, though, and since (unlike some folks) I have no axe to grind, there's no reason for me to do that. I just like talking about electronics. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: John Larkin on 17 Jun 2010 22:15
On Thu, 17 Jun 2010 17:01:54 -0400, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >Jim Thompson wrote: >> On Thu, 17 Jun 2010 12:58:30 -0400, Phil Hobbs >> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >> >>> John Larkin wrote: >>>> On Thu, 17 Jun 2010 09:44:44 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>>> >> [snip] >>>> The base voltage needs to be +1 jd for the thing to oscillate at >>>> equilibrium. The clamp device, c-b junction or schottky, has about the >>>> same tc, but in the opposite direction. In the c-b case (with a low >>>> secondary swing, not some awful class C thrashing, and a big base cap, >>>> so it's not a blocking oscillator) the collector swing that pulls >>>> current out of the base capacitor touches zero, near where the >>>> transistor saturates. In fact, the tc of the c-b junction is canceling >>>> the tc of the e-b junction. Not perfectly, because they are >>>> effectively used at different currents. Because of reverse beta, some >>>> of the tank energy can be clamped through the emitter, which is a bit >>>> negative at that instant. But even that current flow happens when the >>>> c-b junction is forward biased. >>>> >>>> Schottky: suppose we need +0.6 on the base for stable oscillation. The >>>> collector will dip down to, say, 0.3, the schottky will conduct and >>>> pull charge out of the base cap, and it will stabilize there. The tc's >>>> almost cancel. If you assume the amplitude limiting is just brute >>>> clamping of the swing, the tc's still cancel. No saturation, since the >>>> c-b junction doesn't get forward biased. This assumes you've chosen a >>>> suitable base resistor, not jamming too much current into the base, >>>> and the transistor has reasonable beta. >>>> >>>> Actually, the base AGC thing must be happening. With small feedback >>>> voltage into the emitter, a sim shows that the transistor is on >>>> throughout the cycle, "class A." So Ic ~= beta * Ib, on average. >>>> Average Ic would be large if the current through the base resistor >>>> were all actually going into the base. But it's not: the base cap is >>>> being discharged at the negative swing of the collector, stealing base >>>> current and reducing transconductance, and that is exquisitely >>>> sensitive to p-p amplitude. Some tank energy does of course get lost >>>> to the emitter... both mechanisms are at work. Fortunately, both >>>> stabilize the amplitude. >>>> >>>> In my sim, if you short the tank, the supply current goes up about >>>> 30x. (Hmmm, Rb could be bigger!) Output swing is 10.11 volts p-p with >>>> a 5-volt supply. >>>> >>>> Several people have modeled this circuit with small base caps and low >>>> transformer ratios and lots of base bias current. That works >>>> differently. >>>> >>>> John >>> Interesting, thanks. I agree that the Baker clamp pretty well fixes the >>> saturation problem. >>> >>> Cheers >>> >>> Phil Hobbs >> >> Phil, Don't you have means to simulate Larkin's oscillator? >> >> If you bothered to do that you'd find some of Larkin's statements >> above are _absolutely_ incorrect, and others are so hand-waving as to >> be hilarious. >> >> But, hey! Ignorant young bucks with no knowledge of basics are good >> for business :-) >> >> ...Jim Thompson > >Of course I have. > >I'm hip deep in measuring very small nonlinearities in InGaAs >photodiodes just now, How do you do that? Summing on/off light sources? I guess the question is, how small? John |