Twin T circuit wanted
in [Design]
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From: John Fields on 10 Jun 2010 15:06 On Thu, 10 Jun 2010 09:36:33 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Thu, 10 Jun 2010 11:02:49 -0500, John Fields ><jfields(a)austininstruments.com> wrote: >>>Can you think of other ways to make a very frequency and amplitude >>>stable sine wave using early-70s technology? I suppose that a square >>>wave generator and bandpass filter would work, but that's more parts. >>> >>>Got any ideas? >> >>--- >>Tuning fork oscillator. > >Why would that be amplitude stable? --- Please...
From: BlindBaby on 10 Jun 2010 15:08 On Thu, 10 Jun 2010 09:37:04 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Thu, 10 Jun 2010 09:08:33 -0700, BlindBaby ><BlindMelonChitlin(a)wellnevergetthatonethealbumcover.org> wrote: > >>On Thu, 10 Jun 2010 11:02:49 -0500, John Fields >><jfields(a)austininstruments.com> wrote: >> >>>On Thu, 10 Jun 2010 08:06:23 -0700, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On Thu, 10 Jun 2010 07:13:42 -0500, John Fields >>>><jfields(a)austininstruments.com> wrote: >>>> >>>>>On Wed, 09 Jun 2010 20:42:20 -0700, John Larkin >>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>> >>>>>>On 9 Jun 2010 18:54:01 -0700, Winfield Hill >>>>>><Winfield_member(a)newsguy.com> wrote: >>>>>> >>>>>>>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? >>>>>> >>>>>>The peak detection can put a tiny flat on the negative swing of the >>>>>>sine wave. A small resistor in series with the collector fixes that >>>>>>and doesn't seem to do a lot of harm otherwise. >>>>>> >>>>>>> >>>>>>>> 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? >>>>>> >>>>>> >>>>>>But he didn't insult your wife, too. >>>>>> >>>>>> >>>>>>> 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). >>>>>> >>>>>> >>>>>>Oh, picky picky. It's actually, probably, a bit more complex, since >>>>>>the emitter is a little negative at the instant of collision, and the >>>>>>transistor is almost saturating, so some of the stolen base current is >>>>>>going into the collector and some is going into the emitter. It would >>>>>>be interesting to simulate, just to see where the currents really go. >>>>>>Adding the collector resistor changes things, too. >>>>> >>>>>--- >>>>>So simulate it; I posted a working circuit list earlier if you can >>>>>bear to use it without rancor getting in the way. >>>>>--- >>>>> >>>>>>But the AGC thing does work, and the TC is close to zero. >>>>> >>>>>--- >>>>>Serendipitous, no doubt, unless you intentionally designed it in. >>>>> >>>>>Did you? >>>> >>>> >>>>Of course I did. As I noted, I needed a very amplitude-stable sinewave >>>>source for the C5A inclinometer thing. This was a long time before DDS >>>>and DAC versions were feasible. >>>> >>>>Can you think of other ways to make a very frequency and amplitude >>>>stable sine wave using early-70s technology? I suppose that a square >>>>wave generator and bandpass filter would work, but that's more parts. >>>> >>>>Got any ideas? >>> >>>--- >>>Tuning fork oscillator. >> >> Crystal oven? What did 'Tek' and HP use on their scopes for a >>reference? > >Why would that be amplitude stable? > >John You use the oven to trigger the controlled oscillator.
From: John Fields on 10 Jun 2010 15:10 On Thu, 10 Jun 2010 11:37:12 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Thu, 10 Jun 2010 09:46:13 -0700, BlindBaby ><BlindMelonChitlin(a)wellnevergetthatonethealbumcover.org> wrote: > >>On Wed, 09 Jun 2010 10:30:37 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>This will shock the kiddies, but it *is* possible to design circuits >>>without using Spice. Usually it's faster and better. >> >> >> It is usually faster, but these days, not usually better. And the >>speed gain is only about the operator of the sim package, not the sim. >>A good sim app user can beat you, hands down, and have reliable numbers >>to compare with real builds as well. >> >> Sim apps have gotten orders of magnitude tighter in their iterative >>analysis and inclusion of parasitics, etc. >> >> Far better than you, with or without your bench. > >Simulation is like breadboarding. Neither is designing. --- Then what's your problem?
From: BlindBaby on 10 Jun 2010 15:12 On Thu, 10 Jun 2010 14:10:05 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Thu, 10 Jun 2010 11:37:12 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Thu, 10 Jun 2010 09:46:13 -0700, BlindBaby >><BlindMelonChitlin(a)wellnevergetthatonethealbumcover.org> wrote: >> >>>On Wed, 09 Jun 2010 10:30:37 -0700, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>This will shock the kiddies, but it *is* possible to design circuits >>>>without using Spice. Usually it's faster and better. >>> >>> >>> It is usually faster, but these days, not usually better. And the >>>speed gain is only about the operator of the sim package, not the sim. >>>A good sim app user can beat you, hands down, and have reliable numbers >>>to compare with real builds as well. >>> >>> Sim apps have gotten orders of magnitude tighter in their iterative >>>analysis and inclusion of parasitics, etc. >>> >>> Far better than you, with or without your bench. >> >>Simulation is like breadboarding. Neither is designing. > >--- >Then what's your problem? That one might slip past a few of the folks here, including its target.
From: John Larkin on 10 Jun 2010 15:15
On Thu, 10 Jun 2010 13:59:14 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Thu, 10 Jun 2010 09:01:11 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Thu, 10 Jun 2010 09:09:55 -0500, John Fields >><jfields(a)austininstruments.com> wrote: >> >>>On Thu, 10 Jun 2010 06:56:15 -0700, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On Thu, 10 Jun 2010 07:27:47 -0500, John Fields >>>><jfields(a)austininstruments.com> wrote: >>>> >>>>>On Wed, 09 Jun 2010 21:01:19 -0700, John Larkin >>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>> >>>>>>On Wed, 09 Jun 2010 16:02:57 -0500, John Fields >>>>>><jfields(a)austininstruments.com> wrote: >>>>>> >>>>>>>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. >>>>>> >>>>>>SPICE 1 was introduced at a conference in 1973. It wasn't very good, >>>>>>and SPICE 2, 1975, was better. DRAMS were introduced in 1970. >>>>> >>>>>--- >>>>>Red herring, cheater, or, at the very least, ignoratio elenchi. >>>> >>>> >>>>The first few generations of RAM were designed before Spice existed, >>>>which you declared to be "not possible." >>>> >>>>I don't know how to say that in Latin. >>> >>>--- >>>Pity, as is your lack of Englishy reading comprehension, since the >>>point which was being made was that even though you pooh-pooh SPICE, >>>your livelihood, today, depends on it. >> >>I don't think so. People designed radar, magnetrons and klystrons and >>waveguides and servos and all that, without computers. They did the >>math. Early computers were obviously designed without help from >>computers. >> >>I don't use Spice a lot, and could certainly get along without it. It >>is helpful when evaluating nonlinear systems, where math solutions get >>messy. > >--- >I don't know why you're being so argumentative when it's as clear as >the nose on your face that if SPICE didn't exist you'd have very >little on your plate to offer for sale. > That's crazy. I sold stuff before Spice was invented. Maybe you did, too. >A couple of posts back I wrote: > >"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." > >SPICE is an acronym for "Simulation Program with Integrated Circuit >Emphasis", and I'm pretty sure you use chips designed using SPICE so >even if you don't simulate circuits at the board level, SPICE is still >in there. > >Also, SPICE is being used successfully in general circuit simulation >all around the world, so your naysaying is largely falling on ears >that know better. > >Personally, I've been doing circuit design for almost 50 years and I >used to avoid simulators like the plague. > >I've been using LTSpice for 3 or 4 years now and although I can get >along without it, there's no reason on earth I'd want to since typing >is a whole lot easier than wire-wrapping. Spice can be useful but, like breadboarding, it can devolve to fiddling with a circuit until it seems to work. John |