Twin T circuit wanted
in [Basics]
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From: John Fields on 9 Jun 2010 17:02 On Wed, 09 Jun 2010 10:30:37 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Wed, 09 Jun 2010 11:31:31 -0500, John Fields ><jfields(a)austininstruments.com> wrote: > >>On Tue, 08 Jun 2010 15:09:51 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>If I claimed that there was nitrogen in the air, he and >>>JF would hack a Spice simulation and prove me wrong. >> >>--- >>You're being absurd, as usual, but it seems you lucked out this time >>and your oscillator works in LTspice. >> >> > >Since we manufactured and sold lots of them before Spice was >available, and they worked just fine, the luck is on Spice's part. Or >yours. > >This will shock the kiddies, but it *is* possible to design circuits >without using Spice. Usually it's faster and better. --- You're preaching to the choir, bucko. In your world, maybe, but when you're talking circuits with hundreds of thousands or millions of transistors, it's not possible. This may come as a surprise to you, but many (if not most) of the circuits which you buy and incorporate into your products were designed using SPICE, so the fact that you assemble them into working product that you don't simulate doesn't mean it's free of SPICE.
From: Jim Thompson on 9 Jun 2010 19:43 On Mon, 07 Jun 2010 20:33:23 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: [snip] > >The cool thing is that the collector swing is almost exactly 2xVcc >peak-to-peak. As the amplitude builds up, at the negative swing peak >the emitter goes a little bit negative, to get out of the way, and the >collector swings to just about ground. That forward-biases the c-b >junction and discharges the base cap, reducing transistor base current >hence gain. So it has a built-in peak detecting AGC amplitude >levelling loop with close to zero TC. All from 5 parts. Or sometimes >six. > [snip] I know John won't respond, but could someone, perhaps Win, tell me how the "AGC" works? ...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: Phil Hobbs on 9 Jun 2010 20:40 John Larkin wrote: > On Wed, 09 Jun 2010 11:31:31 -0500, John Fields > <jfields(a)austininstruments.com> wrote: > >> On Tue, 08 Jun 2010 15:09:51 -0700, John Larkin >> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>> If I claimed that there was nitrogen in the air, he and >>> JF would hack a Spice simulation and prove me wrong. >> --- >> You're being absurd, as usual, but it seems you lucked out this time >> and your oscillator works in LTspice. >> >> > > Since we manufactured and sold lots of them before Spice was > available, and they worked just fine, the luck is on Spice's part. Or > yours. > > This will shock the kiddies, but it *is* possible to design circuits > without using Spice. Usually it's faster and better. > > John I'm not a big SPICE user in general, though I've done more SPICEing in the last year than in the 20 previous. For some things, such as really weird photodiode preamps where nonlinear capacitances and so on are important, it can help a lot--provided the models are semi-decent. For most other things, I prefer algebra. You learn a lot more about how the circuit works by crunching the math than by poking the simulation until it seems to work. 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 9 Jun 2010 21:19 On Wed, 09 Jun 2010 20:40:37 -0400, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >John Larkin wrote: >> On Wed, 09 Jun 2010 11:31:31 -0500, John Fields >> <jfields(a)austininstruments.com> wrote: >> >>> On Tue, 08 Jun 2010 15:09:51 -0700, John Larkin >>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>> If I claimed that there was nitrogen in the air, he and >>>> JF would hack a Spice simulation and prove me wrong. >>> --- >>> You're being absurd, as usual, but it seems you lucked out this time >>> and your oscillator works in LTspice. >>> >>> >> >> Since we manufactured and sold lots of them before Spice was >> available, and they worked just fine, the luck is on Spice's part. Or >> yours. >> >> This will shock the kiddies, but it *is* possible to design circuits >> without using Spice. Usually it's faster and better. >> >> John > >I'm not a big SPICE user in general, though I've done more SPICEing in >the last year than in the 20 previous. > >For some things, such as really weird photodiode preamps where nonlinear >capacitances and so on are important, it can help a lot--provided the >models are semi-decent. For most other things, I prefer algebra. You >learn a lot more about how the circuit works by crunching the math than >by poking the simulation until it seems to work. > >Cheers > >Phil Hobbs Spice is handy for tweaking control loops, especially higher-order loops that matter, or when anything nonlinear is going on. Or when you don't have a hard definition of what "right" is. Simple opamp type things are better to do with guesswork, or a scribbled Bode plot. You lose points if you use a calculator. Spice is good for filters, too. I did a constant-voltage/constant-current crossover power supply sort of thing recently, analog ORing two loop error signals, with a wide range of possible customer loads, and it was great for tweaking. The actual implementation will be firmware. The other good use for Spice is grinding out the numbers on voltage dividers, pure DC analysis, just to save a lot of calculator stuff. We never simulate whole products, or even whole circuits, just little pieces, or control loop abstractions. John
From: Winfield Hill on 9 Jun 2010 21:54
Jim Thompson wrote... > > John Larkin wrote: > > [snip] >> >> The cool thing is that the collector swing is almost exactly 2xVcc >> peak-to-peak. As the amplitude builds up, at the negative swing peak >> the emitter goes a little bit negative, to get out of the way, and the >> collector swings to just about ground. That forward-biases the c-b >> junction and discharges the base cap, reducing transistor base current >> hence gain. So it has a built-in peak detecting AGC amplitude >> leveling loop with close to zero TC. All from 5 parts. Or sometimes >> six. What's the 6th part, I wonder? > I know John won't respond, but could someone, perhaps Win, tell me > how the "AGC" works? I'm sure he would, but why should I, over the years you've insulted me at least as much as him, and perhaps more aggressively? Anyway, he did explain it, SFAICT. Note the BJT is over-biased - plenty of base current, that if left unchecked would charge the base-to-ground capacitor and over-current the transistor. So the oscillator runs and examining cycle-by-cycle, the collector swings higher and higher until it goes negative with respect to the base voltage, close to saturating the transistor, and turning on the base-collector diode a bit, robbing current from the base capacitor. This process servos the BJT current to just the right level to sustain an oscillation collector-voltage level where just the right amount of current is robbed each cycle to control the base voltage. Thereby insuring that the collector goes close to the emitter on each cycle, establishing a tightly-controlled amplitude, which as John pointed out, is temperature independent to first order since Vce(sat) is relatively temperature independent. John said Vcc peak, but actually it must be closer to Vcc - Vce(sat). -- Thanks, - Win |