On Wed, 15 Aug 2012 23:21:07 -0500, "Tim Williams" <tmoranwms@charter.net> wrote:>"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in >message news:5jmo28h8uq1ilq9najgnnbtkql2bjrcke9@4ax.com... >> Happy or hoppy? Most "craft" beers are way too bitter for my taste, >> and most gourmet red wines are way too tannic. Just got some nice >> wheat ale that my engineers brewed at home... gotta try it. > >I like darker things, there's a lot of good stouts, porters and ales >around here. Hops can be good and bad. Something like, say, Heineken, is >very hoppy but also light and drinkable. A lot of lagers are excessively >hopped and unappealing. > >> Hey, how about this? >> >> https://dl.dropbox.com/u/53724080/Circuits/Isrc_simpler.JPG >> >> Ludicrously simple. No Miller nonsense. Might not oscillate. MMBTH81 >> would have about 2 pF out, or BFT92 would have about 0.75 but lower >> beta. > >I don't see a cap helping you there. Ccb puts signal directly on the >op-amp, coupling the active node to its nonlinearity, and Cbe in turn >couples this to R_E, which puts a (second degree) resistor back in the >circuit. Might as well use a ferrite bead, but you already know how >sloppy that works out. > >Better to use a cascode, where the "outer" transistor is as close to the >active node as possible, with as little base resistance as possible (just >enough to keep it stable), so you get Ccb incorporated as closely as >possible into the node. At that point if you still need temp or bias >compensation, you won't be any worse off, and you'll most likely be much >better off than any other method. > >TimEven the cascode stage would benefit from an added b-e cap. It (should) kill any tendency to oscillate, and it allows the base to be stiff, without a quenching resistor, which will kill Miller effects. With a big b-e cap on the cascode PNP, the upper current source can be a pokey mosfet, with lots of capacitance but no beta error. https://dl.dropbox.com/u/53724080/Circuits/Isrc_Cascode.JPG -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
fast ramp follies
Started by ●August 14, 2012
Reply by ●August 16, 20122012-08-16
Reply by ●August 16, 20122012-08-16
On Aug 15, 10:43=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> Hey, how about this? > > https://dl.dropbox.com/u/53724080/Circuits/Isrc_simpler.JPGIt's kind of a variation on Phil's active inductor. That defeats all the oscillation modes I can think of so far. (c-b, e-b, c-e)(Which means little, since circuits are so ingenious inventing new ones.)> Ludicrously simple. No Miller nonsense. Might not oscillate. MMBTH81 > would have about 2 pF out, or BFT92 would have about 0.75 but lower > beta.You could use the beta-cancellation trick. But, stray and parasitic capacitance will be big factors compared to a 10pF integration cap.> If this works, I should have done it years ago.-- Cheers, James Arthur
Reply by ●August 16, 20122012-08-16
On Thu, 16 Aug 2012 07:39:04 -0700 (PDT), dagmargoodboat@yahoo.com wrote:>On Aug 15, 10:43�pm, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> Hey, how about this? >> >> https://dl.dropbox.com/u/53724080/Circuits/Isrc_simpler.JPG > >It's kind of a variation on Phil's active inductor. That defeats all >the oscillation modes I can think of so far. (c-b, e-b, c-e)(Which >means little, since circuits are so ingenious inventing new ones.) > >> Ludicrously simple. No Miller nonsense. Might not oscillate. MMBTH81 >> would have about 2 pF out, or BFT92 would have about 0.75 but lower >> beta. > >You could use the beta-cancellation trick. But, stray and parasitic >capacitance will be big factors compared to a 10pF integration cap. > >> If this works, I should have done it years ago.Yup. But I'd still add a base resistor, for the very reasons Gerhard Hoffmann brought up... the output Z of the OpAmp is a big unknown (*). (*) Which brings to mind... maybe add some DC load to the OpAmp to keep it out of the class-B region. ...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 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●August 16, 20122012-08-16
On Thu, 16 Aug 2012 08:29:46 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On Thu, 16 Aug 2012 07:39:04 -0700 (PDT), dagmargoodboat@yahoo.com >wrote: > >>On Aug 15, 10:43�pm, John Larkin >><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> >>> Hey, how about this? >>> >>> https://dl.dropbox.com/u/53724080/Circuits/Isrc_simpler.JPG >> >>It's kind of a variation on Phil's active inductor. That defeats all >>the oscillation modes I can think of so far. (c-b, e-b, c-e)(Which >>means little, since circuits are so ingenious inventing new ones.) >> >>> Ludicrously simple. No Miller nonsense. Might not oscillate. MMBTH81 >>> would have about 2 pF out, or BFT92 would have about 0.75 but lower >>> beta. >> >>You could use the beta-cancellation trick. But, stray and parasitic >>capacitance will be big factors compared to a 10pF integration cap. >> >>> If this works, I should have done it years ago. > >Yup. But I'd still add a base resistor, for the very reasons Gerhard >Hoffmann brought up... the output Z of the OpAmp is a big unknown (*).The base and emitter are shorted at AC. The opamp Zout doesn't matter any more.> >(*) Which brings to mind... maybe add some DC load to the OpAmp to >keep it out of the class-B region.LM7301 is a r-r output design. It isn't an ancient class-B like an LM324. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by ●August 16, 20122012-08-16
On Thu, 16 Aug 2012 08:41:53 -0700, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:>On Thu, 16 Aug 2012 08:29:46 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >>On Thu, 16 Aug 2012 07:39:04 -0700 (PDT), dagmargoodboat@yahoo.com >>wrote: >> >>>On Aug 15, 10:43�pm, John Larkin >>><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >>> >>>> Hey, how about this? >>>> >>>> https://dl.dropbox.com/u/53724080/Circuits/Isrc_simpler.JPG >>> >>>It's kind of a variation on Phil's active inductor. That defeats all >>>the oscillation modes I can think of so far. (c-b, e-b, c-e)(Which >>>means little, since circuits are so ingenious inventing new ones.) >>> >>>> Ludicrously simple. No Miller nonsense. Might not oscillate. MMBTH81 >>>> would have about 2 pF out, or BFT92 would have about 0.75 but lower >>>> beta. >>> >>>You could use the beta-cancellation trick. But, stray and parasitic >>>capacitance will be big factors compared to a 10pF integration cap. >>> >>>> If this works, I should have done it years ago. >> >>Yup. But I'd still add a base resistor, for the very reasons Gerhard >>Hoffmann brought up... the output Z of the OpAmp is a big unknown (*). > >The base and emitter are shorted at AC. The opamp Zout doesn't matter >any more.Whatever. I assume no responsibility for any dumb stunts you attempt.> >> >>(*) Which brings to mind... maybe add some DC load to the OpAmp to >>keep it out of the class-B region. > >LM7301 is a r-r output design. It isn't an ancient class-B like an >LM324.It can still have dead-band. Though my own rail-to-rail designs go class-A at the crossover ;-) My design done exactly one year ago does +/-100mA rail-to-rail from +3.3V supply, yet avoids dead-band... but I _am_ the greatest ;-) ...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 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●August 16, 20122012-08-16
On Thu, 16 Aug 2012 09:36:04 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On Thu, 16 Aug 2012 08:41:53 -0700, John Larkin ><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: > >>On Thu, 16 Aug 2012 08:29:46 -0700, Jim Thompson >><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >> >>>On Thu, 16 Aug 2012 07:39:04 -0700 (PDT), dagmargoodboat@yahoo.com >>>wrote: >>> >>>>On Aug 15, 10:43�pm, John Larkin >>>><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >>>> >>>>> Hey, how about this? >>>>> >>>>> https://dl.dropbox.com/u/53724080/Circuits/Isrc_simpler.JPG >>>> >>>>It's kind of a variation on Phil's active inductor. That defeats all >>>>the oscillation modes I can think of so far. (c-b, e-b, c-e)(Which >>>>means little, since circuits are so ingenious inventing new ones.) >>>> >>>>> Ludicrously simple. No Miller nonsense. Might not oscillate. MMBTH81 >>>>> would have about 2 pF out, or BFT92 would have about 0.75 but lower >>>>> beta. >>>> >>>>You could use the beta-cancellation trick. But, stray and parasitic >>>>capacitance will be big factors compared to a 10pF integration cap. >>>> >>>>> If this works, I should have done it years ago. >>> >>>Yup. But I'd still add a base resistor, for the very reasons Gerhard >>>Hoffmann brought up... the output Z of the OpAmp is a big unknown (*). >> >>The base and emitter are shorted at AC. The opamp Zout doesn't matter >>any more. > >Whatever. I assume no responsibility for any dumb stunts you attempt.Or, apparently, for making sense.> >> >>> >>>(*) Which brings to mind... maybe add some DC load to the OpAmp to >>>keep it out of the class-B region. >> >>LM7301 is a r-r output design. It isn't an ancient class-B like an >>LM324. > >It can still have dead-band. Though my own rail-to-rail designs go >class-A at the crossover ;-) > >My design done exactly one year ago does +/-100mA rail-to-rail from >+3.3V supply, yet avoids dead-band... but I _am_ the greatest ;-)So you keep telling us, without evidence. Greatest asshole, actually. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●August 16, 20122012-08-16
On Thu, 16 Aug 2012 10:13:27 -0700, John Larkin <jlarkin@highlandtechnology.com> wrote:>On Thu, 16 Aug 2012 09:36:04 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >>On Thu, 16 Aug 2012 08:41:53 -0700, John Larkin >><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Thu, 16 Aug 2012 08:29:46 -0700, Jim Thompson >>><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >>> >>>>On Thu, 16 Aug 2012 07:39:04 -0700 (PDT), dagmargoodboat@yahoo.com >>>>wrote: >>>> >>>>>On Aug 15, 10:43�pm, John Larkin >>>>><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >>>>> >>>>>> Hey, how about this? >>>>>> >>>>>> https://dl.dropbox.com/u/53724080/Circuits/Isrc_simpler.JPG >>>>> >>>>>It's kind of a variation on Phil's active inductor. That defeats all >>>>>the oscillation modes I can think of so far. (c-b, e-b, c-e)(Which >>>>>means little, since circuits are so ingenious inventing new ones.) >>>>> >>>>>> Ludicrously simple. No Miller nonsense. Might not oscillate. MMBTH81 >>>>>> would have about 2 pF out, or BFT92 would have about 0.75 but lower >>>>>> beta. >>>>> >>>>>You could use the beta-cancellation trick. But, stray and parasitic >>>>>capacitance will be big factors compared to a 10pF integration cap. >>>>> >>>>>> If this works, I should have done it years ago. >>>> >>>>Yup. But I'd still add a base resistor, for the very reasons Gerhard >>>>Hoffmann brought up... the output Z of the OpAmp is a big unknown (*). >>> >>>The base and emitter are shorted at AC. The opamp Zout doesn't matter >>>any more. >> >>Whatever. I assume no responsibility for any dumb stunts you attempt. > >Or, apparently, for making sense. > > >> >>> >>>> >>>>(*) Which brings to mind... maybe add some DC load to the OpAmp to >>>>keep it out of the class-B region. >>> >>>LM7301 is a r-r output design. It isn't an ancient class-B like an >>>LM324. >> >>It can still have dead-band. Though my own rail-to-rail designs go >>class-A at the crossover ;-) >> >>My design done exactly one year ago does +/-100mA rail-to-rail from >>+3.3V supply, yet avoids dead-band... but I _am_ the greatest ;-) > >So you keep telling us, without evidence.I can't divulge proprietary information, which, if you had half a brain, you'd understand. However, anyone who doubts my competency, feel free to call TLSI (631-470-8880, on Long Island), ask for Dr. Zhigang Ma, or Nicolas Salamina, and ask them what they think of my work. Ask about the power OpAmp. Then call me if you'd like something similar on _your_ custom chip :-) Larkin's opinion matters not... with his head all the way up his posterior orifice he sees nothing but his own turd-laden ideas.> >Greatest asshole, actually.Nope. You hold that title. ...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 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●August 16, 20122012-08-16
On Wed, 15 Aug 2012 19:43:40 -0700, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: <snip>>Hey, how about this? > >https://dl.dropbox.com/u/53724080/Circuits/Isrc_simpler.JPG > >Ludicrously simple. No Miller nonsense. Might not oscillate. MMBTH81 >would have about 2 pF out, or BFT92 would have about 0.75 but lower >beta. > >If this works, I should have done it years ago.I thought you wanted it to switch? RL
Reply by ●August 16, 20122012-08-16
On Wednesday, August 15, 2012 1:17:18 PM UTC-7, (unknown) wrote:> On Aug 15, 2:58=A0pm, whit3rd <whit...@gmail.com> wrote: >=20 > > On Monday, August 13, 2012 8:49:33 PM UTC-7, John Larkin wrote: >=20 > > > On Mon, 13 Aug 2012 20:38:56 -0700, miso <m...@sushi.com> wrote: >=20 > > >=20 > > > >> OK, I need to charge a capacitor with a stable constant current. T=he>=20 > > >=20 > > > >> desired slope is about a volt per nanosecond. >=20 > > > >I'd be more inclined to cascode the current source output rather tha=n>=20 > > >=20 > > > >add an inductor. >=20 > > >=20 > > > Would that help? The beta error would increase, and cascodes can >=20 > > >=20 > > > oscillate >=20 > > >=20 > > If beta 'error' is a problem,...> > you can add a transistor base resistor and feed back to the op amp >=20 > > to completely remove base current=20 > Is this the one you're thinking of? >=20 > http://groups.google.com/group/sci.electronics.design/browse_thread/threa=d/5bcae9656debc0f5/35371afc2d377036?hl=3Den&lnk=3Dgst&q=3Dresistor+compenat= e+arthur#35371afc2d377036>=20Looks like the same thing; BAD ASCII ART FOLLOWS +---- 47k-----+ (Iout) | | | | |\ | | Vref>--1k----+---| \ | |/ | >---+--+---47ohm----+--| +---|-/ | | | | |/ =3D | |\ +----------+---+--47k------+ V | | +--1k------------+ | (1ohm) | GND The use of a cascode can be folded into this scheme, by (1) using matched transistors for the cascode (2) doubling the feedback (to compensate two base currents, while only sensing one). A 1.2V reference as well as 2.5V = cascode base bias can be had from a LV431 style programmable zener; set it for 2.5V and the sense node gives you a stable 1.25V..
Reply by ●August 16, 20122012-08-16
On Aug 16, 11:29=A0am, Jim Thompson <To-Email-Use-The-Envelope-I...@On- My-Web-Site.com> wrote:> On Thu, 16 Aug 2012 07:39:04 -0700 (PDT), dagmargoodb...@yahoo.com > wrote: > > > > > > > > > > >On Aug 15, 10:43=A0pm, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > > >> Hey, how about this? > > >>https://dl.dropbox.com/u/53724080/Circuits/Isrc_simpler.JPG > > >It's kind of a variation on Phil's active inductor. =A0That defeats all > >the oscillation modes I can think of so far. (c-b, e-b, c-e)(Which > >means little, since circuits are so ingenious inventing new ones.) > > >> Ludicrously simple. No Miller nonsense. Might not oscillate. MMBTH81 > >> would have about 2 pF out, or BFT92 would have about 0.75 but lower > >> beta. > > >You could use the beta-cancellation trick. =A0But, stray and parasitic > >capacitance will be big factors compared to a 10pF integration cap. > > >> If this works, I should have done it years ago. > > Yup. =A0But I'd still add a base resistor, for the very reasons Gerhard > Hoffmann brought up... the output Z of the OpAmp is a big unknown (*). > > (*) Which brings to mind... maybe add some DC load to the OpAmp to > keep it out of the class-B region.I agree with both those points, and meant to mention them. I don't trust the op-amp to behave nicely to impulses, or its output to be stiff. I'd expect the output to be hi-z on this timescale. If anything I'd be tempted to bypass the bjt's base to the supply rail. The BJT then handles the fast stuff. Isolate that capacitive load from the op amp's output with a series resistor, and stabilize the op amp loop itself with a feed-forward cap. Standard stuff. Does it all matter? Unclamping the integration cap will feed-thru a small impulse through to the bjt / CCS. After that, it's pretty clean. So, the op-amp's output impedance might not matter, but I suspect it will. I invented loading LM324 outputs all by myself waayyyy back as a punk kid, to stiffen them up and kill the crossover THD. Of course everyone else on the planet thought of it too. :-) -- Cheers, James Arthur
