Reply by Hul Tytus March 30, 20172017-03-30
Familiar numbers. Nice to see the correct ones.

Hul

tabbypurr@gmail.com wrote:
> On Thursday, 30 March 2017 04:18:18 UTC+1, Tim Wescott wrote: > > On Wed, 29 Mar 2017 22:54:13 +0000, Hul Tytus wrote: > > > > > Tim - the early opamps (lm707??) required "compensation" so that the > > > loop gain was less than unity at the frequency where the phase shift was > > > 180 degrees. The first opamp that completely compensated itself, ie > > > could be used at unity gain with no weird behavior, was, I think, the > > > single version of the lm747. > > > Those versions that required compensation had special pins for > > > capacitors. But the circuitry between the output and the negative input > > > could also be used for compensation, that is to reduce the loop gain > > > with a low frequency rc filter. That is probably what you were doing > > > with the rail to rail opamp. A 1K resister and 20 pf creates a 3 db > > > point around 8 mhz or so. > > > > I got out of college just as those weren't being used much any more.
> The 709 was the popular uncompensated one, and the 741 the number 1 unity stable opamp for a long time. There were others of course before & after, eg the 702. And even valve opamps.
> NT
Reply by Hul Tytus March 30, 20172017-03-30
Jim - I was familiar with the Motorola devices in the late 60's; those and 
RCA's but mostly the Fairchild opamp's, but that was mostly due to 
available purchasing channels.
   Fun times those. If one device was announced with break through 
features in the spring, there'd be a better one in the fall. 
Congratulations on a device that lasted 53 years. That's no mean 
accomplishment.   

Hul


Jim Thompson <To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote:
> On Wed, 29 Mar 2017 22:54:13 +0000 (UTC), Hul Tytus <ht@panix.com> > wrote:
> >Tim - the early opamps (lm707??) required "compensation" so that the loop > >gain was less than unity at the frequency where the phase shift was 180 > >degrees. The first opamp that completely compensated itself, ie could be > >used at unity gain with no weird behavior, was, I think, the single > >version of the lm747. > > Those versions that required compensation had special pins for > >capacitors. But the circuitry between the output and the negative input > >could also be used for compensation, that is to reduce the loop gain with a > >low frequency rc filter. That is probably what you were doing with the > >rail to rail opamp. A 1K resister and 20 pf creates a 3 db point around 8 > >mhz or so. > > > >Hul > >
> [snip]
> My first OpAmp, MC1530/31, early '60's...
> <http://www.analog-innovations.com/SED/MC1530-DataSheet.pdf>
> was like that, external compensation, sliding-class-A output stage, > still being sold by Lansdale (licensed from Motorola), 53-years later > ;-)
> <http://www.analog-innovations.com/SED/MC1530-TeachingExercise.pdf>
> The military love it... absolutely stable, high-slew-rate for the era, > indefinite-time short-circuit proof. > > ...Jim Thompson > -- > | James E.Thompson | mens | > | Analog Innovations | et | > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > | E-mail Icon at http://www.analog-innovations.com | 1962 |
> Thinking outside the box... producing elegant solutions.
Reply by March 30, 20172017-03-30
On Thursday, 30 March 2017 04:18:18 UTC+1, Tim Wescott  wrote:
> On Wed, 29 Mar 2017 22:54:13 +0000, Hul Tytus wrote: > > > Tim - the early opamps (lm707??) required "compensation" so that the > > loop gain was less than unity at the frequency where the phase shift was > > 180 degrees. The first opamp that completely compensated itself, ie > > could be used at unity gain with no weird behavior, was, I think, the > > single version of the lm747. > > Those versions that required compensation had special pins for > > capacitors. But the circuitry between the output and the negative input > > could also be used for compensation, that is to reduce the loop gain > > with a low frequency rc filter. That is probably what you were doing > > with the rail to rail opamp. A 1K resister and 20 pf creates a 3 db > > point around 8 mhz or so. > > I got out of college just as those weren't being used much any more.
The 709 was the popular uncompensated one, and the 741 the number 1 unity stable opamp for a long time. There were others of course before & after, eg the 702. And even valve opamps. NT
Reply by Tim Wescott March 30, 20172017-03-30
On Wed, 29 Mar 2017 22:54:13 +0000, Hul Tytus wrote:

> Tim - the early opamps (lm707??) required "compensation" so that the > loop gain was less than unity at the frequency where the phase shift was > 180 degrees. The first opamp that completely compensated itself, ie > could be used at unity gain with no weird behavior, was, I think, the > single version of the lm747. > Those versions that required compensation had special pins for > capacitors. But the circuitry between the output and the negative input > could also be used for compensation, that is to reduce the loop gain > with a low frequency rc filter. That is probably what you were doing > with the rail to rail opamp. A 1K resister and 20 pf creates a 3 db > point around 8 mhz or so.
I got out of college just as those weren't being used much any more. -- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
Reply by George Herold March 29, 20172017-03-29
On Wednesday, March 29, 2017 at 9:30:04 PM UTC-4, George Herold wrote:
> On Wednesday, March 29, 2017 at 7:31:31 PM UTC-4, Jim Thompson wrote: > > On Wed, 29 Mar 2017 22:54:13 +0000 (UTC), Hul Tytus <ht@panix.com> > > wrote: > > > > >Tim - the early opamps (lm707??) required "compensation" so that the loop > > >gain was less than unity at the frequency where the phase shift was 180 > > >degrees. The first opamp that completely compensated itself, ie could be > > >used at unity gain with no weird behavior, was, I think, the single > > >version of the lm747. > > > Those versions that required compensation had special pins for > > >capacitors. But the circuitry between the output and the negative input > > >could also be used for compensation, that is to reduce the loop gain with a > > >low frequency rc filter. That is probably what you were doing with the > > >rail to rail opamp. A 1K resister and 20 pf creates a 3 db point around 8 > > >mhz or so. > > > > > >Hul > > > > > > > [snip] > > > > My first OpAmp, MC1530/31, early '60's... > > > > <http://www.analog-innovations.com/SED/MC1530-DataSheet.pdf> > > > > was like that, external compensation, sliding-class-A output stage, > > still being sold by Lansdale (licensed from Motorola), 53-years later > > ;-) > > > > <http://www.analog-innovations.com/SED/MC1530-TeachingExercise.pdf> > Huh!!, I was going to ask what "sliding Class A was". > (I first try to be a "class A" kind of guy... ) > Thanks for the exercise.. I'm going to have to think about it. >
Oh, I didn't see you gave me all the equations too! GH.
> George H. > > The military love it... absolutely stable, high-slew-rate for the era, > > indefinite-time short-circuit proof. > > > > ...Jim Thompson > > -- > > | James E.Thompson | mens | > > | Analog Innovations | et | > > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > > | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | > > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > > | E-mail Icon at http://www.analog-innovations.com | 1962 | > > > > Thinking outside the box... producing elegant solutions.
Reply by George Herold March 29, 20172017-03-29
On Wednesday, March 29, 2017 at 7:31:31 PM UTC-4, Jim Thompson wrote:
> On Wed, 29 Mar 2017 22:54:13 +0000 (UTC), Hul Tytus <ht@panix.com> > wrote: > > >Tim - the early opamps (lm707??) required "compensation" so that the loop > >gain was less than unity at the frequency where the phase shift was 180 > >degrees. The first opamp that completely compensated itself, ie could be > >used at unity gain with no weird behavior, was, I think, the single > >version of the lm747. > > Those versions that required compensation had special pins for > >capacitors. But the circuitry between the output and the negative input > >could also be used for compensation, that is to reduce the loop gain with a > >low frequency rc filter. That is probably what you were doing with the > >rail to rail opamp. A 1K resister and 20 pf creates a 3 db point around 8 > >mhz or so. > > > >Hul > > > > [snip] > > My first OpAmp, MC1530/31, early '60's... > > <http://www.analog-innovations.com/SED/MC1530-DataSheet.pdf> > > was like that, external compensation, sliding-class-A output stage, > still being sold by Lansdale (licensed from Motorola), 53-years later > ;-) > > <http://www.analog-innovations.com/SED/MC1530-TeachingExercise.pdf>
Huh!!, I was going to ask what "sliding Class A was". (I first try to be a "class A" kind of guy... ) Thanks for the exercise.. I'm going to have to think about it. George H.
> The military love it... absolutely stable, high-slew-rate for the era, > indefinite-time short-circuit proof. > > ...Jim Thompson > -- > | James E.Thompson | mens | > | Analog Innovations | et | > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > | E-mail Icon at http://www.analog-innovations.com | 1962 | > > Thinking outside the box... producing elegant solutions.
Reply by Jim Thompson March 29, 20172017-03-29
On Wed, 29 Mar 2017 22:54:13 +0000 (UTC), Hul Tytus <ht@panix.com>
wrote:

>Tim - the early opamps (lm707??) required "compensation" so that the loop >gain was less than unity at the frequency where the phase shift was 180 >degrees. The first opamp that completely compensated itself, ie could be >used at unity gain with no weird behavior, was, I think, the single >version of the lm747. > Those versions that required compensation had special pins for >capacitors. But the circuitry between the output and the negative input >could also be used for compensation, that is to reduce the loop gain with a >low frequency rc filter. That is probably what you were doing with the >rail to rail opamp. A 1K resister and 20 pf creates a 3 db point around 8 >mhz or so. > >Hul >
[snip] My first OpAmp, MC1530/31, early '60's... <http://www.analog-innovations.com/SED/MC1530-DataSheet.pdf> was like that, external compensation, sliding-class-A output stage, still being sold by Lansdale (licensed from Motorola), 53-years later ;-) <http://www.analog-innovations.com/SED/MC1530-TeachingExercise.pdf> The military love it... absolutely stable, high-slew-rate for the era, indefinite-time short-circuit proof. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Thinking outside the box... producing elegant solutions.
Reply by Hul Tytus March 29, 20172017-03-29
Tim - the early opamps (lm707??) required "compensation" so that the loop 
gain was less than unity at the frequency where the phase shift was 180 
degrees. The first opamp that completely compensated itself, ie could be 
used at unity gain with no weird behavior, was, I think, the single 
version of the lm747. 
   Those versions that required compensation had special pins for
capacitors. But the circuitry between the output and the negative input 
could also be used for compensation, that is to reduce the loop gain with a 
low frequency rc filter. That is probably what you were doing with the 
rail to rail opamp. A 1K resister and 20 pf creates a 3 db point around 8 
mhz or so.

Hul

Tim Wescott <tim@seemywebsite.com> wrote:
> On Tue, 28 Mar 2017 15:17:14 -0700, Lasse Langwadt Christensen wrote:
> > Den onsdag den 29. marts 2017 kl. 00.12.54 UTC+2 skrev Tim Wescott: > >> So, about a decade and a half ago, I worked with some very ill-tempered > >> rail-rail opamps. They were among the first-generation rail-rail amps, > >> and they had the "nice" feature that in spite of their specified > >> behavior, they'd go unstable as a voltage follower if you just > >> connected the output to the negative input -- but they'd work fine if > >> you did so through a 1k-ohm resistor. > >> > >> I got into the habit of putting a resistor there in my voltage > >> followers. > >> > >> I just discovered an error in a circuit of mine that uses TSV912 > >> op-amps, > >> connected as voltage followers, with 22K-ohm resistors from output to > >> input. I'm having a very "d'oh" moment, because I'm thinking that if > >> you DO want resistors there at all, you really want something in the > >> 200-ohm to 1k-ohm range. Habit, I think, kneecapped me. > >> > >> So, I'm going to experiment around with the best value for this, but > >> does anyone have any suggestions as to how to figure out what to use? > >> Was that old ill-tempered op-amp that I used Back Then a fluke, or is > >> it generally advantageous to use a resistor in the feedback path of a > >> voltage follower? > >> > >> Suggestions welcome. > > > > https://e2e.ti.com/blogs_/b/precisionhub/archive/2014/07/15/resistors- > in-the-feedback-of-a-buffer-ask-why
> Thanks. Zeroing out the resistance solves the problem, although it does > leave me with "d'oh" stamped on my forehead.
> Unfortunately, it doesn't solve the problem that my customer is fighting > in Baltimore, at the same time that it _does_ solve the symptoms that I > was seeing in my test setup here on the west coast. We've been plagued > by this all along, alas.
> -- > Tim Wescott > Control systems, embedded software and circuit design > I'm looking for work! See my website if you're interested > http://www.wescottdesign.com
Reply by Tim Wescott March 29, 20172017-03-29
On Tue, 28 Mar 2017 15:17:14 -0700, Lasse Langwadt Christensen wrote:

> Den onsdag den 29. marts 2017 kl. 00.12.54 UTC+2 skrev Tim Wescott: >> So, about a decade and a half ago, I worked with some very ill-tempered >> rail-rail opamps. They were among the first-generation rail-rail amps, >> and they had the "nice" feature that in spite of their specified >> behavior, they'd go unstable as a voltage follower if you just >> connected the output to the negative input -- but they'd work fine if >> you did so through a 1k-ohm resistor. >> >> I got into the habit of putting a resistor there in my voltage >> followers. >> >> I just discovered an error in a circuit of mine that uses TSV912 >> op-amps, >> connected as voltage followers, with 22K-ohm resistors from output to >> input. I'm having a very "d'oh" moment, because I'm thinking that if >> you DO want resistors there at all, you really want something in the >> 200-ohm to 1k-ohm range. Habit, I think, kneecapped me. >> >> So, I'm going to experiment around with the best value for this, but >> does anyone have any suggestions as to how to figure out what to use? >> Was that old ill-tempered op-amp that I used Back Then a fluke, or is >> it generally advantageous to use a resistor in the feedback path of a >> voltage follower? >> >> Suggestions welcome. > > https://e2e.ti.com/blogs_/b/precisionhub/archive/2014/07/15/resistors-
in-the-feedback-of-a-buffer-ask-why Thanks. Zeroing out the resistance solves the problem, although it does leave me with "d'oh" stamped on my forehead. Unfortunately, it doesn't solve the problem that my customer is fighting in Baltimore, at the same time that it _does_ solve the symptoms that I was seeing in my test setup here on the west coast. We've been plagued by this all along, alas. -- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
Reply by George Herold March 29, 20172017-03-29
On Tuesday, March 28, 2017 at 6:12:54 PM UTC-4, Tim Wescott wrote:
> So, about a decade and a half ago, I worked with some very ill-tempered > rail-rail opamps. They were among the first-generation rail-rail amps, > and they had the "nice" feature that in spite of their specified > behavior, they'd go unstable as a voltage follower if you just connected > the output to the negative input -- but they'd work fine if you did so > through a 1k-ohm resistor. > > I got into the habit of putting a resistor there in my voltage followers. > > I just discovered an error in a circuit of mine that uses TSV912 op-amps, > connected as voltage followers, with 22K-ohm resistors from output to > input. I'm having a very "d'oh" moment, because I'm thinking that if you > DO want resistors there at all, you really want something in the 200-ohm > to 1k-ohm range. Habit, I think, kneecapped me. > > So, I'm going to experiment around with the best value for this, but does > anyone have any suggestions as to how to figure out what to use? Was > that old ill-tempered op-amp that I used Back Then a fluke, or is it > generally advantageous to use a resistor in the feedback path of a > voltage follower? > > Suggestions welcome. > > -- > > Tim Wescott > Wescott Design Services > http://www.wescottdesign.com > > I'm looking for work -- see my website!
Not rail to rail, but I've put 500 ohms in the OPA227's following figure 37 here, http://www.ti.com/lit/ds/symlink/opa227.pdf as current limiting resistors. George H.