Reply by George Herold August 1, 20132013-08-01
On Wednesday, July 31, 2013 4:12:12 PM UTC-4, cassiope wrote:
> On Wed, 31 Jul 2013 10:17:28 -0700, George Herold wrote: > >
<snip>
> > Thanks for all the advice. I just can't 'spend' anymore time on this > > project. (As much as I'd like to chase down the different opamp > > weirdnesses.) RE the TLE2142 and bias current. It's a simple buffer, > > with switched input resistors to ground on the front end. I don't know > > how I could compensate for the current.. would I have to put switched > > resistors in the feedback? 100k ohm of feedback may come with it's own > > problem. > > You only need to provide a current source at the opamp input. According > to the datasheet this current is pretty stable so you might be able to get > away with a resistor between amplifier and tweak wiper, and the tweak element > ends between ground and the appropriate supply voltage. If you need > a higher impedance value you can always connect the resistor to a bipolar > transistor's emitter, and take the compensation current from the transistor's > base, using the beta to reduce the current and increase the impedance.
Ahh, (silly me.) Well that's an easy tweak. I'll give it a try. (The board needs another spin to make some solder holes bigger anyway.)
> > > But it's always important to recognize when to stop working on something.
Sometimes that's the hardest thing to know. (When it's time to stop.) George H.
> > > > For the opa2604 ringies it's there with no coax. (just a double male > > > barrel connector into scope.) Alas I have no low C probes. (The 'best' > > > x10 has 16pF) > > >> > > >> > > >> > > >> If you really like the TLE2142 - how about compensating for the input > > >> bias? > > >> > > >> Yes, it would cost a tweak. > > >> > > >> > > >> > > >> >> If your customers are savvy enough to diagnose the problem, and > > >> >> replace > > >> > > >> > > >> >> > > >> >> the amplifier without damage to themselves or to the device or to > > >> > > >> >> whatever > > >> > > >> > > >> >> > > >> >> function they were meant to provide - sure. My users, while often > > >> > > >> >> PhDs, > > >> > > >> > > >> >> > > >> >> are most often not that electronically savvy. And down-time is > > >> > > >> >> expensive. > > >> > > >> > > >> > > > >> > Grin.. well PhD's are often less of the 'hand's on' type. But the > > >> > > >> > circuit is pretty easy. I made it through hole, so if someoen wanted > > >> > to > > >> > > >> > change things it would be easier. http://bayimg.com/PAoKiAaEa > > >> > > >> > > >> > > > >> > The ugly pot in the middle will go away. (just changing the supply > > >> > > >> > voltage.) I let it cook over night at ~100C. no issues in the > > >> > morning. > > >> > > >> > > >> > > >> Ok, that seems simple and your users are presumably knowledgeable about > > >> > > >> antistatic issues, etc. > > >> > > >> > > >> > > >> > I'll test the heat again with lower supply voltage (but with the > > >> > palstic > > >> > > >> > cover in place.) > > >> > > >> > > >> > > > >> > So what type of PhD's do you service? Can you tell us where you > > >> > work? > > >> > > >> > > >> > > > >> > George H. > > >> > > >> > > >> > > >> Ah... the devices we design and build are for a collection of > > >> neuroscientists. > > >> > > >> Many have some electronics skills but most of them have enough on their > > >> > > >> minds trying to understand and/or manipulate the brain. > > > > > > Thanks, sounds interesting. There was a research/ medical doctor/ > > > biologist who came visiting. I was looking at the step response of an > > > amplifier on the 'scope. And I told him it was a two pole butterworth > > > low pass. "Hmm", he says, "the delay looks a bit long there." pointing > > > at the trace. "Oh there's also a series 1 k ohm resistor in the circuit > > > so maybe that slows it down.", I respond. I shorted out the 1 k ohm. > > > And he was happy. Now that's something you don't see every day. A > > > doctor who *really* knows his step response. (Needless to say, they do > > > a lot of electronics in his lab.) > > > > > > George H.
Reply by Jim Thompson July 31, 20132013-07-31
On Wed, 31 Jul 2013 20:12:12 +0000 (UTC), Frank Miles
<fpm@u.washington.edu> wrote:

>On Wed, 31 Jul 2013 10:17:28 -0700, George Herold wrote: > >[snip] >>> Hmmn, just noticed that the GBW of the TLE2142 is about 1/4 of the >>> OPA2604 >>> >>> GBW. That might be part of why you see the problem with the OPA but >>> not the TLE. >>> >>> The 'ring', after all, is near the unity-gain BW of the TLE. And you >>> only >>> >>> see the problem with some length of coax attached? Does it occur with >>> no coax, >>> >>> just probing with a good low-Cin 10x or FET probe? Could you plug in a >>> much faster >>> >>> amplifier while temporarily running at a lower voltage to see if >>> there's a problem >>> >>> with your circuit or its implementation? >> >> Thanks for all the advice. I just can't 'spend' anymore time on this >> project. (As much as I'd like to chase down the different opamp >> weirdnesses.) RE the TLE2142 and bias current. It's a simple buffer, >> with switched input resistors to ground on the front end. I don't know >> how I could compensate for the current.. would I have to put switched >> resistors in the feedback? 100k ohm of feedback may come with it's own >> problem. > >You only need to provide a current source at the opamp input. According >to the datasheet this current is pretty stable so you might be able to get >away with a resistor between amplifier and tweak wiper, and the tweak element >ends between ground and the appropriate supply voltage. If you need >a higher impedance value you can always connect the resistor to a bipolar >transistor's emitter, and take the compensation current from the transistor's >base, using the beta to reduce the current and increase the impedance. > >But it's always important to recognize when to stop working on something. > >> For the opa2604 ringies it's there with no coax. (just a double male >> barrel connector into scope.) Alas I have no low C probes. (The 'best' >> x10 has 16pF) >>> >>> >>> >>> If you really like the TLE2142 - how about compensating for the input >>> bias? >>> >>> Yes, it would cost a tweak. >>> >>> >>> >>> >> If your customers are savvy enough to diagnose the problem, and >>> >> replace >>> >>> >>> >> >>> >> the amplifier without damage to themselves or to the device or to >>> >>> >> whatever >>> >>> >>> >> >>> >> function they were meant to provide - sure. My users, while often >>> >>> >> PhDs, >>> >>> >>> >> >>> >> are most often not that electronically savvy. And down-time is >>> >>> >> expensive. >>> >>> >>> > >>> > Grin.. well PhD's are often less of the 'hand's on' type. But the >>> >>> > circuit is pretty easy. I made it through hole, so if someoen wanted >>> > to >>> >>> > change things it would be easier. http://bayimg.com/PAoKiAaEa >>> >>> >>> > >>> > The ugly pot in the middle will go away. (just changing the supply >>> >>> > voltage.) I let it cook over night at ~100C. no issues in the >>> > morning. >>> >>> >>> >>> Ok, that seems simple and your users are presumably knowledgeable about >>> >>> antistatic issues, etc. >>> >>> >>> >>> > I'll test the heat again with lower supply voltage (but with the >>> > palstic >>> >>> > cover in place.) >>> >>> >>> > >>> > So what type of PhD's do you service? Can you tell us where you >>> > work? >>> >>> >>> > >>> > George H. >>> >>> >>> >>> Ah... the devices we design and build are for a collection of >>> neuroscientists. >>> >>> Many have some electronics skills but most of them have enough on their >>> >>> minds trying to understand and/or manipulate the brain. >> >> Thanks, sounds interesting. There was a research/ medical doctor/ >> biologist who came visiting. I was looking at the step response of an >> amplifier on the 'scope. And I told him it was a two pole butterworth >> low pass. "Hmm", he says, "the delay looks a bit long there." pointing >> at the trace. "Oh there's also a series 1 k ohm resistor in the circuit >> so maybe that slows it down.", I respond. I shorted out the 1 k ohm. >> And he was happy. Now that's something you don't see every day. A >> doctor who *really* knows his step response. (Needless to say, they do >> a lot of electronics in his lab.) >> >> George H.
I haven't seen any I/O _specifications_. I'd attack it with a suitable OpAmp meeting the input current requirements and tack on a discrete output stage that would be unperturbed by the "HV". ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 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 Frank Miles July 31, 20132013-07-31
On Wed, 31 Jul 2013 10:17:28 -0700, George Herold wrote:

[snip]
>> Hmmn, just noticed that the GBW of the TLE2142 is about 1/4 of the >> OPA2604 >> >> GBW. That might be part of why you see the problem with the OPA but >> not the TLE. >> >> The 'ring', after all, is near the unity-gain BW of the TLE. And you >> only >> >> see the problem with some length of coax attached? Does it occur with >> no coax, >> >> just probing with a good low-Cin 10x or FET probe? Could you plug in a >> much faster >> >> amplifier while temporarily running at a lower voltage to see if >> there's a problem >> >> with your circuit or its implementation? > > Thanks for all the advice. I just can't 'spend' anymore time on this > project. (As much as I'd like to chase down the different opamp > weirdnesses.) RE the TLE2142 and bias current. It's a simple buffer, > with switched input resistors to ground on the front end. I don't know > how I could compensate for the current.. would I have to put switched > resistors in the feedback? 100k ohm of feedback may come with it's own > problem.
You only need to provide a current source at the opamp input. According to the datasheet this current is pretty stable so you might be able to get away with a resistor between amplifier and tweak wiper, and the tweak element ends between ground and the appropriate supply voltage. If you need a higher impedance value you can always connect the resistor to a bipolar transistor's emitter, and take the compensation current from the transistor's base, using the beta to reduce the current and increase the impedance. But it's always important to recognize when to stop working on something.
> For the opa2604 ringies it's there with no coax. (just a double male > barrel connector into scope.) Alas I have no low C probes. (The 'best' > x10 has 16pF) >> >> >> >> If you really like the TLE2142 - how about compensating for the input >> bias? >> >> Yes, it would cost a tweak. >> >> >> >> >> If your customers are savvy enough to diagnose the problem, and >> >> replace >> >> >> >> >> >> the amplifier without damage to themselves or to the device or to >> >> >> whatever >> >> >> >> >> >> function they were meant to provide - sure. My users, while often >> >> >> PhDs, >> >> >> >> >> >> are most often not that electronically savvy. And down-time is >> >> >> expensive. >> >> >> > >> > Grin.. well PhD's are often less of the 'hand's on' type. But the >> >> > circuit is pretty easy. I made it through hole, so if someoen wanted >> > to >> >> > change things it would be easier. http://bayimg.com/PAoKiAaEa >> >> >> > >> > The ugly pot in the middle will go away. (just changing the supply >> >> > voltage.) I let it cook over night at ~100C. no issues in the >> > morning. >> >> >> >> Ok, that seems simple and your users are presumably knowledgeable about >> >> antistatic issues, etc. >> >> >> >> > I'll test the heat again with lower supply voltage (but with the >> > palstic >> >> > cover in place.) >> >> >> > >> > So what type of PhD's do you service? Can you tell us where you >> > work? >> >> >> > >> > George H. >> >> >> >> Ah... the devices we design and build are for a collection of >> neuroscientists. >> >> Many have some electronics skills but most of them have enough on their >> >> minds trying to understand and/or manipulate the brain. > > Thanks, sounds interesting. There was a research/ medical doctor/ > biologist who came visiting. I was looking at the step response of an > amplifier on the 'scope. And I told him it was a two pole butterworth > low pass. "Hmm", he says, "the delay looks a bit long there." pointing > at the trace. "Oh there's also a series 1 k ohm resistor in the circuit > so maybe that slows it down.", I respond. I shorted out the 1 k ohm. > And he was happy. Now that's something you don't see every day. A > doctor who *really* knows his step response. (Needless to say, they do > a lot of electronics in his lab.) > > George H.
Reply by George Herold July 31, 20132013-07-31
On Wednesday, July 31, 2013 12:05:32 PM UTC-4, cassiope wrote:
> On Wed, 31 Jul 2013 07:16:26 -0700, George Herold wrote: >=20 >=20 >=20 > > On Tuesday, July 30, 2013 2:27:09 PM UTC-4, cassiope wrote: >=20 > >> On Tue, 30 Jul 2013 11:12:30 -0700, George Herold wrote: >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> > On Tuesday, July 30, 2013 12:51:41 PM UTC-4, cassiope wrote: >=20 > > <snip> >=20 > >=20 >=20 > >=20 >=20 > >> >> Did you try the compensation circuits given in the spec sheet? BB >=20 > >> >> (TI) >=20 > >>=20 >=20 > >> >> shows some input RC circuits that help when driving capacitive load=
s
>=20 > >>=20 >=20 > >> >> with this amplifier. >=20 > >> > No. I'm not sure it was the cable C that was the issue. (Only 3 foo=
t
>=20 > >> > of >=20 > >>=20 >=20 > >> > coax and shrinking that to a few inches didn't change a thing.) I >=20 > >> > did >=20 > >>=20 >=20 > >> > put 50 ohms in series. >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> Ah - you hadn't mentioned that before. Hmmn - could you describe the >=20 > >> ringing >=20 > >>=20 >=20 > >> (amplitude, duration, ringing frequency)? >=20 > >=20 >=20 > > Better than that here's some 'scope shots! >=20 > >=20 >=20 > > So I=92m looking at avalanche breakdown voltages with different quenchi=
ng
>=20 > > resistors (100k and 10 k) the first two =91scope shots are with the >=20 > > opa2134 100k ohm >=20 > > //bayimg.com/MaoKGaaEA >=20 > > 10k ohm >=20 > > //bayimg.com/NAoKDAAea >=20 > >=20 >=20 > > Oh and here=92s the TLE2142 with 10 k ohm //bayimg.com/nAOKGaaEa >=20 > >=20 >=20 > > And now the opa2604 first 100 k >=20 > > //bayimg.com/naokHaAEa >=20 > > and 10 k >=20 > > //bayimg.com/naOkjaaea >=20 > >=20 >=20 > > This is before I added a 50 ohm series resistor. That gave the bumps a >=20 > > longer period but a bit higher amplitude. >=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > >=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> >> > So I figured I'd try over voltaging the opa2134's I've got the >=20 > >> >> > supply >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> >> > voltage up to 40V (36V max) and no magic smoke yet. :^) I tired a >=20 > >> >> > few >=20 > >>=20 >=20 > >> >> >> > different pieces, and did a bit of turn on/off torture. The >=20 > >> >> >> > circuit >=20 > >>=20 >=20 > >> >> > has >=20 > >>=20 >=20 > >> >> > now been running on the lab bench for several hours. Should I >=20 > >> >> > test >=20 > >>=20 >=20 > >> >> > with >=20 > >>=20 >=20 > >> >> > some elevated temperatures? I'm thinking this opamp will be fine. >=20 > >>=20 >=20 > >> >> > (I'll >=20 > >>=20 >=20 > >> >> > design for 35 V supplies and worse case it'll only be a tad above >=20 > >> >> > 36 >=20 > >>=20 >=20 > >> >> > volts.) (tad =3D 400mV in this case) >=20 > >>=20 >=20 > >>=20 >=20 > >> >>=20 >=20 > >>=20 >=20 > >> >>=20 >=20 > >>=20 >=20 > >> >>=20 >=20 > >> >> What kind of reliability do you need? If this is a short-term >=20 > >> >> one-off, >=20 > >>=20 >=20 > >> >> you can probably get away with this kind of brinksmanship. If it >=20 > >> >> has >=20 > >>=20 >=20 > >> >> to work for others over a longer time period - do everyone a favor >=20 > >> >> and >=20 > >>=20 >=20 > >> >> either use a part rated for higher voltage or modify your circuit >=20 > >> >> (e.g. >=20 > >>=20 >=20 > >> >> composite amplifier) such that the amplifiers aren't overstressed. >=20 > >>=20 >=20 > >>=20 >=20 > >> >=20 >=20 > >> > Brinksmanship(?).. It's only 0.4V?.. and that's for worst case. We'l=
l
>=20 > >>=20 >=20 > >> > sell maybe 100 or so of these over several years. >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> I'm pretty conservative when it comes to semiconductor voltages - I'd >=20 > >> call >=20 > >>=20 >=20 > >> 0.4V _less_ than rated voltage was brinksmanship. But I expect my >=20 > >> designs >=20 > >>=20 >=20 > >> to have "reasonably high" reliability (not medical/life support level)=
.
>=20 > >>=20 >=20 > >> If you look at failure rate curves with voltage (and I admit I don't >=20 > >> recall >=20 > >>=20 >=20 > >> seeing any for more modern lower voltage opamps) they are climbing >=20 > >> rapidly >=20 > >>=20 >=20 > >> and smoothly in the vicinity of the rated voltage. Of course there is >=20 > >> a >=20 > >>=20 >=20 > >> significant amount of variation. >=20 > >>=20 >=20 > >>=20 >=20 > >> =20 >=20 > >> > So can you say anything more about the stress? What's the cause? >=20 > >>=20 >=20 > >> > I tried hitting the one on the bench with a heat gun, and shorted >=20 > >> > the >=20 > >>=20 >=20 > >> > output. (The case rose to ~100 C. I should see what happens with >=20 > >>=20 >=20 > >> > only 36V.) Hey, I'll stick it in a socket. That way if it does >=20 > >> > fry >=20 > >>=20 >=20 > >> > in the future it can be replaced. (opamps are cheap.) >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 >=20 >=20 > Hmmn, just noticed that the GBW of the TLE2142 is about 1/4 of the OPA260=
4
>=20 > GBW. That might be part of why you see the problem with the OPA but not =
the TLE.
>=20 > The 'ring', after all, is near the unity-gain BW of the TLE. And you onl=
y
>=20 > see the problem with some length of coax attached? Does it occur with no=
coax,
>=20 > just probing with a good low-Cin 10x or FET probe? Could you plug in a m=
uch faster
>=20 > amplifier while temporarily running at a lower voltage to see if there's =
a problem
>=20 > with your circuit or its implementation?
Thanks for all the advice. I just can't 'spend' anymore time on this proje= ct. (As much as I'd like to chase down the different opamp weirdnesses.) = =20 RE the TLE2142 and bias current. It's a simple buffer, with switched input= resistors to ground on the front end. I don't know how I could compensate= for the current.. would I have to put switched resistors in the feedback? = 100k ohm of feedback may come with it's own problem. =20 For the opa2604 ringies it's there with no coax. (just a double male barre= l connector into scope.) Alas I have no low C probes. (The 'best' x10 has= 16pF) =20
>=20 >=20 >=20 > If you really like the TLE2142 - how about compensating for the input bia=
s?
>=20 > Yes, it would cost a tweak. >=20 >=20 >=20 > >> If your customers are savvy enough to diagnose the problem, and replac=
e
>=20 > >>=20 >=20 > >> the amplifier without damage to themselves or to the device or to >=20 > >> whatever >=20 > >>=20 >=20 > >> function they were meant to provide - sure. My users, while often >=20 > >> PhDs, >=20 > >>=20 >=20 > >> are most often not that electronically savvy. And down-time is >=20 > >> expensive. >=20 > >=20 >=20 > > Grin.. well PhD's are often less of the 'hand's on' type. But the >=20 > > circuit is pretty easy. I made it through hole, so if someoen wanted t=
o
>=20 > > change things it would be easier. http://bayimg.com/PAoKiAaEa >=20 > >=20 >=20 > > The ugly pot in the middle will go away. (just changing the supply >=20 > > voltage.) I let it cook over night at ~100C. no issues in the morning=
.
>=20 >=20 >=20 > Ok, that seems simple and your users are presumably knowledgeable about >=20 > antistatic issues, etc. >=20 >=20 >=20 > > I'll test the heat again with lower supply voltage (but with the palsti=
c
>=20 > > cover in place.) >=20 > >=20 >=20 > > So what type of PhD's do you service? Can you tell us where you work? >=20 > > =20 >=20 > > George H. >=20 >=20 >=20 > Ah... the devices we design and build are for a collection of neuroscient=
ists.
>=20 > Many have some electronics skills but most of them have enough on their >=20 > minds trying to understand and/or manipulate the brain.
Thanks, sounds interesting. There was a research/ medical doctor/ biologi= st who came visiting. I was looking at the step response of an amplifier o= n the 'scope. And I told him it was a two pole butterworth low pass. =20 "Hmm", he says, "the delay looks a bit long there." pointing at the trace. = =20 "Oh there's also a series 1 k ohm resistor in the circuit so maybe that slo= ws it down.", I respond. =20 I shorted out the 1 k ohm. And he was happy. =20 Now that's something you don't see every day. A doctor who *really* knows = his step response. (Needless to say, they do a lot of electronics in his l= ab.) =20 George H.
Reply by Frank Miles July 31, 20132013-07-31
On Wed, 31 Jul 2013 07:16:26 -0700, George Herold wrote:

> On Tuesday, July 30, 2013 2:27:09 PM UTC-4, cassiope wrote: >> On Tue, 30 Jul 2013 11:12:30 -0700, George Herold wrote: >> >> >> >> > On Tuesday, July 30, 2013 12:51:41 PM UTC-4, cassiope wrote: > <snip> > > >> >> Did you try the compensation circuits given in the spec sheet? BB >> >> (TI) >> >> >> shows some input RC circuits that help when driving capacitive loads >> >> >> with this amplifier. >> > No. I'm not sure it was the cable C that was the issue. (Only 3 foot >> > of >> >> > coax and shrinking that to a few inches didn't change a thing.) I >> > did >> >> > put 50 ohms in series. >> >> >> >> Ah - you hadn't mentioned that before. Hmmn - could you describe the >> ringing >> >> (amplitude, duration, ringing frequency)? > > Better than that here's some 'scope shots! > > So I&rsquo;m looking at avalanche breakdown voltages with different quenching > resistors (100k and 10 k) the first two &lsquo;scope shots are with the > opa2134 100k ohm > //bayimg.com/MaoKGaaEA > 10k ohm > //bayimg.com/NAoKDAAea > > Oh and here&rsquo;s the TLE2142 with 10 k ohm //bayimg.com/nAOKGaaEa > > And now the opa2604 first 100 k > //bayimg.com/naokHaAEa > and 10 k > //bayimg.com/naOkjaaea > > This is before I added a 50 ohm series resistor. That gave the bumps a > longer period but a bit higher amplitude. > > > > >> >> >> >> > So I figured I'd try over voltaging the opa2134's I've got the >> >> > supply >> >> >> >> >> > voltage up to 40V (36V max) and no magic smoke yet. :^) I tired a >> >> > few >> >> >> >> > different pieces, and did a bit of turn on/off torture. The >> >> >> > circuit >> >> >> > has >> >> >> > now been running on the lab bench for several hours. Should I >> >> > test >> >> >> > with >> >> >> > some elevated temperatures? I'm thinking this opamp will be fine. >> >> >> > (I'll >> >> >> > design for 35 V supplies and worse case it'll only be a tad above >> >> > 36 >> >> >> > volts.) (tad = 400mV in this case) >> >> >> >> >> >> >> >> >> >> >> >> What kind of reliability do you need? If this is a short-term >> >> one-off, >> >> >> you can probably get away with this kind of brinksmanship. If it >> >> has >> >> >> to work for others over a longer time period - do everyone a favor >> >> and >> >> >> either use a part rated for higher voltage or modify your circuit >> >> (e.g. >> >> >> composite amplifier) such that the amplifiers aren't overstressed. >> >> >> > >> > Brinksmanship(?).. It's only 0.4V?.. and that's for worst case. We'll >> >> > sell maybe 100 or so of these over several years. >> >> >> >> I'm pretty conservative when it comes to semiconductor voltages - I'd >> call >> >> 0.4V _less_ than rated voltage was brinksmanship. But I expect my >> designs >> >> to have "reasonably high" reliability (not medical/life support level). >> >> If you look at failure rate curves with voltage (and I admit I don't >> recall >> >> seeing any for more modern lower voltage opamps) they are climbing >> rapidly >> >> and smoothly in the vicinity of the rated voltage. Of course there is >> a >> >> significant amount of variation. >> >> >> >> > So can you say anything more about the stress? What's the cause? >> >> > I tried hitting the one on the bench with a heat gun, and shorted >> > the >> >> > output. (The case rose to ~100 C. I should see what happens with >> >> > only 36V.) Hey, I'll stick it in a socket. That way if it does >> > fry >> >> > in the future it can be replaced. (opamps are cheap.) >> >> >>
Hmmn, just noticed that the GBW of the TLE2142 is about 1/4 of the OPA2604 GBW. That might be part of why you see the problem with the OPA but not the TLE. The 'ring', after all, is near the unity-gain BW of the TLE. And you only see the problem with some length of coax attached? Does it occur with no coax, just probing with a good low-Cin 10x or FET probe? Could you plug in a much faster amplifier while temporarily running at a lower voltage to see if there's a problem with your circuit or its implementation? If you really like the TLE2142 - how about compensating for the input bias? Yes, it would cost a tweak.
>> If your customers are savvy enough to diagnose the problem, and replace >> >> the amplifier without damage to themselves or to the device or to >> whatever >> >> function they were meant to provide - sure. My users, while often >> PhDs, >> >> are most often not that electronically savvy. And down-time is >> expensive. > > Grin.. well PhD's are often less of the 'hand's on' type. But the > circuit is pretty easy. I made it through hole, so if someoen wanted to > change things it would be easier. http://bayimg.com/PAoKiAaEa > > The ugly pot in the middle will go away. (just changing the supply > voltage.) I let it cook over night at ~100C. no issues in the morning.
Ok, that seems simple and your users are presumably knowledgeable about antistatic issues, etc.
> I'll test the heat again with lower supply voltage (but with the palstic > cover in place.) > > So what type of PhD's do you service? Can you tell us where you work? > > George H.
Ah... the devices we design and build are for a collection of neuroscientists. Many have some electronics skills but most of them have enough on their minds trying to understand and/or manipulate the brain.
Reply by George Herold July 31, 20132013-07-31
On Tuesday, July 30, 2013 4:50:23 PM UTC-4, John Larkin wrote:
> On Tue, 30 Jul 2013 08:11:59 -0700 (PDT), George Herold >=20 > <gherold@teachspin.com> wrote: >=20 >=20 >=20 > >On Monday, July 15, 2013 12:01:21 PM UTC-4, George Herold wrote: >=20 > >> Opamp Vsupply >36V >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> Hi all, I=92ve got a circuit with that uses an opa2134. I find mysel=
f pushing the 36V supply limit and I=92m a little worried. So I went look= ing for a similar opamp but with a bit more headroom. =20
>=20 > >>=20 >=20 > >> So specs might read, >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> Dual opamp >=20 > >>=20 >=20 > >> unity gain stable=20 >=20 > >>=20 >=20 > >> 4(+) Mhz BW (8MHz or more would be nicer) >=20 > >>=20 >=20 > >> 10 V/us slew (again more is better) >=20 > >>=20 >=20 > >> 20mA current (positive, again more would be nicer) >=20 > >>=20 >=20 > >> small input C ( <5pF would be nice.) >=20 > >>=20 >=20 > >> 8 pin dip preferred >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> Trolling digikey I found a few possible candidates. =20 >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> TLE2142 (6 MHz GBW) >=20 > >>=20 >=20 > >> TLE2072 (only 38 V supply, 11 pF input C) >=20 > >>=20 >=20 > >> OPA2604 (nice but 10 pF input C)=20 >=20 > >>=20 >=20 > >> (I=92ll order a few of each.) >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> There was also the LF412A, but a bit lacking is positive supply curren=
t. =20
>=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> Any others that I might have missed? =20 >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> Thanks,=20 >=20 > >>=20 >=20 > >> George H. >=20 > > >=20 > >Hi all, I finally had time to try out these other opamps. =20 >=20 > >(it was a fail on each one.) >=20 > >The TLE2142 was a sweet opamp. But I forgot about the bias current. =20 >=20 > >I've got a variable source impedance (100k ,33k and 10k ohm) and the ~1u=
A of bias current means 10mV to 100 mV of DC offset. (not acceptable.) To= o bad 'cause otherwise it was nice.
>=20 > > >=20 > >The TLE2142 has an issue running near it's negative rail. It needed the=
rail to be -3.0 Volts to keep the DC offset below 5mV (When operated from = -1.5 V's the offset was ~120mV!)
>=20 > > >=20 > >The OPA2604 oscillated out of the box and needed a bit of feedback C to =
tame it. (not a problem.) But it also had a lot of 'issues' (ringy dingie= s) when driving a coax cable. I mucked around with termination resistors (= source and end.) but never got the 'ringies' down to an acceptable level. = =20
>=20 > > >=20 > >So I figured I'd try over voltaging the opa2134's I've got the supply vo=
ltage up to 40V (36V max) and no magic smoke yet. :^) =20
>=20 > >I tired a few different pieces, and did a bit of turn on/off torture. =
=20
>=20 > >The circuit has now been running on the lab bench for several hours. Sh=
ould I test with some elevated temperatures? =20
>=20 > >I'm thinking this opamp will be fine. (I'll design for 35 V supplies an=
d worse case it'll only be a tad above 36 volts.) (tad =3D 400mV in this ca= se)
>=20 > > >=20 > >George H. >=20 >=20 >=20 > Sounds OK, but it would be better/funner to test the part to failure. >=20 > Maybe it fails at 41, maybe it fails at 70.
Well I could go a bit higher. (power from Phihong 48V wall wart.) But other parts might start to break too. (There's an ref102 that goes to = 40V so I might loose that before the opamp.) =20 George H.
>=20 >=20 >=20 >=20 >=20 > --=20 >=20 >=20 >=20 > John Larkin Highland Technology, Inc >=20 >=20 >=20 > jlarkin at highlandtechnology dot com >=20 > http://www.highlandtechnology.com >=20 >=20 >=20 > Precision electronic instrumentation >=20 > Picosecond-resolution Digital Delay and Pulse generators >=20 > Custom laser drivers and controllers >=20 > Photonics and fiberoptic TTL data links >=20 > VME thermocouple, LVDT, synchro acquisition and simulation
Reply by George Herold July 31, 20132013-07-31
On Tuesday, July 30, 2013 2:27:09 PM UTC-4, cassiope wrote:
> On Tue, 30 Jul 2013 11:12:30 -0700, George Herold wrote: >=20 >=20 >=20 > > On Tuesday, July 30, 2013 12:51:41 PM UTC-4, cassiope wrote:
<snip>
>=20 > >> Did you try the compensation circuits given in the spec sheet? BB (TI=
)
>=20 > >> shows some input RC circuits that help when driving capacitive loads >=20 > >> with this amplifier. > > No. I'm not sure it was the cable C that was the issue. (Only 3 foot o=
f
>=20 > > coax and shrinking that to a few inches didn't change a thing.) I did >=20 > > put 50 ohms in series. >=20 >=20 >=20 > Ah - you hadn't mentioned that before. Hmmn - could you describe the rin=
ging
>=20 > (amplitude, duration, ringing frequency)?
Better than that here's some 'scope shots! =20 So I=92m looking at avalanche breakdown voltages with different quenching r= esistors (100k and 10 k) the first two =91scope shots are with the opa2134 100k ohm //bayimg.com/MaoKGaaEA 10k ohm //bayimg.com/NAoKDAAea Oh and here=92s the TLE2142 with 10 k ohm=20 //bayimg.com/nAOKGaaEa And now the opa2604 first 100 k //bayimg.com/naokHaAEa and 10 k //bayimg.com/naOkjaaea This is before I added a 50 ohm series resistor. That gave the bumps a lon= ger period but a bit higher amplitude. =20
>=20 >=20 >=20 > >> > So I figured I'd try over voltaging the opa2134's I've got the suppl=
y
>=20 >=20 >=20 > >> > voltage up to 40V (36V max) and no magic smoke yet. :^) I tired a fe=
w
>=20 > >> >> > different pieces, and did a bit of turn on/off torture. The circu=
it
>=20 > >> > has >=20 > >> > now been running on the lab bench for several hours. Should I test >=20 > >> > with >=20 > >> > some elevated temperatures? I'm thinking this opamp will be fine.=20 >=20 > >> > (I'll >=20 > >> > design for 35 V supplies and worse case it'll only be a tad above 36 >=20 > >> > volts.) (tad =3D 400mV in this case) >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> What kind of reliability do you need? If this is a short-term one-off=
,
>=20 > >> you can probably get away with this kind of brinksmanship. If it has >=20 > >> to work for others over a longer time period - do everyone a favor and >=20 > >> either use a part rated for higher voltage or modify your circuit (e.g=
.
>=20 > >> composite amplifier) such that the amplifiers aren't overstressed. >=20 > >=20 >=20 > > Brinksmanship(?).. It's only 0.4V?.. and that's for worst case. We'll >=20 > > sell maybe 100 or so of these over several years. >=20 >=20 >=20 > I'm pretty conservative when it comes to semiconductor voltages - I'd cal=
l
>=20 > 0.4V _less_ than rated voltage was brinksmanship. But I expect my design=
s
>=20 > to have "reasonably high" reliability (not medical/life support level). >=20 > If you look at failure rate curves with voltage (and I admit I don't reca=
ll
>=20 > seeing any for more modern lower voltage opamps) they are climbing rapidl=
y
>=20 > and smoothly in the vicinity of the rated voltage. Of course there is a >=20 > significant amount of variation. >=20 > =20 >=20 > > So can you say anything more about the stress? What's the cause? >=20 > > I tried hitting the one on the bench with a heat gun, and shorted the >=20 > > output. (The case rose to ~100 C. I should see what happens with >=20 > > only 36V.) Hey, I'll stick it in a socket. That way if it does fry >=20 > > in the future it can be replaced. (opamps are cheap.) >=20 >=20 >=20 > If your customers are savvy enough to diagnose the problem, and replace >=20 > the amplifier without damage to themselves or to the device or to whateve=
r
>=20 > function they were meant to provide - sure. My users, while often PhDs, >=20 > are most often not that electronically savvy. And down-time is expensive=
. Grin.. well PhD's are often less of the 'hand's on' type. But the circuit = is pretty easy. I made it through hole, so if someoen wanted to change thi= ngs it would be easier.=20 http://bayimg.com/PAoKiAaEa The ugly pot in the middle will go away. (just changing the supply voltage= .) I let it cook over night at ~100C. no issues in the morning. =20 I'll test the heat again with lower supply voltage (but with the palstic co= ver in place.) So what type of PhD's do you service? Can you tell us where you work?=20 =20 George H. =20
Reply by Jim Thompson July 30, 20132013-07-30
On Tue, 30 Jul 2013 13:50:23 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

>On Tue, 30 Jul 2013 08:11:59 -0700 (PDT), George Herold ><gherold@teachspin.com> wrote: > >>On Monday, July 15, 2013 12:01:21 PM UTC-4, George Herold wrote: >>> Opamp Vsupply >36V >>> >>> >>> >>> Hi all, I&#2013266066;ve got a circuit with that uses an opa2134. I find myself pushing the 36V supply limit and I&#2013266066;m a little worried. So I went looking for a similar opamp but with a bit more headroom. >>> >>> So specs might read, >>> >>> >>> >>> Dual opamp >>> >>> unity gain stable >>> >>> 4(+) Mhz BW (8MHz or more would be nicer) >>> >>> 10 V/us slew (again more is better) >>> >>> 20mA current (positive, again more would be nicer) >>> >>> small input C ( <5pF would be nice.) >>> >>> 8 pin dip preferred >>> >>> >>> >>> Trolling digikey I found a few possible candidates. >>> >>> >>> >>> TLE2142 (6 MHz GBW) >>> >>> TLE2072 (only 38 V supply, 11 pF input C) >>> >>> OPA2604 (nice but 10 pF input C) >>> >>> (I&#2013266066;ll order a few of each.) >>> >>> >>> >>> There was also the LF412A, but a bit lacking is positive supply current. >>> >>> >>> >>> Any others that I might have missed? >>> >>> >>> >>> Thanks, >>> >>> George H. >> >>Hi all, I finally had time to try out these other opamps. >>(it was a fail on each one.) >>The TLE2142 was a sweet opamp. But I forgot about the bias current. >>I've got a variable source impedance (100k ,33k and 10k ohm) and the ~1uA of bias current means 10mV to 100 mV of DC offset. (not acceptable.) Too bad 'cause otherwise it was nice. >> >>The TLE2142 has an issue running near it's negative rail. It needed the rail to be -3.0 Volts to keep the DC offset below 5mV (When operated from -1.5 V's the offset was ~120mV!) >> >>The OPA2604 oscillated out of the box and needed a bit of feedback C to tame it. (not a problem.) But it also had a lot of 'issues' (ringy dingies) when driving a coax cable. I mucked around with termination resistors (source and end.) but never got the 'ringies' down to an acceptable level. >> >>So I figured I'd try over voltaging the opa2134's I've got the supply voltage up to 40V (36V max) and no magic smoke yet. :^) >>I tired a few different pieces, and did a bit of turn on/off torture. >>The circuit has now been running on the lab bench for several hours. Should I test with some elevated temperatures? >>I'm thinking this opamp will be fine. (I'll design for 35 V supplies and worse case it'll only be a tad above 36 volts.) (tad = 400mV in this case) >> >>George H. > >Sounds OK, but it would be better/funner to test the part to failure. >Maybe it fails at 41, maybe it fails at 70.
It'll fail at 2.5 "tads", on a humid Sunday, just after midnight, when lightning strikes 3 miles away >:-} ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 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 John Larkin July 30, 20132013-07-30
On Tue, 30 Jul 2013 08:11:59 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On Monday, July 15, 2013 12:01:21 PM UTC-4, George Herold wrote: >> Opamp Vsupply >36V >> >> >> >> Hi all, I&#2013266066;ve got a circuit with that uses an opa2134. I find myself pushing the 36V supply limit and I&#2013266066;m a little worried. So I went looking for a similar opamp but with a bit more headroom. >> >> So specs might read, >> >> >> >> Dual opamp >> >> unity gain stable >> >> 4(+) Mhz BW (8MHz or more would be nicer) >> >> 10 V/us slew (again more is better) >> >> 20mA current (positive, again more would be nicer) >> >> small input C ( <5pF would be nice.) >> >> 8 pin dip preferred >> >> >> >> Trolling digikey I found a few possible candidates. >> >> >> >> TLE2142 (6 MHz GBW) >> >> TLE2072 (only 38 V supply, 11 pF input C) >> >> OPA2604 (nice but 10 pF input C) >> >> (I&#2013266066;ll order a few of each.) >> >> >> >> There was also the LF412A, but a bit lacking is positive supply current. >> >> >> >> Any others that I might have missed? >> >> >> >> Thanks, >> >> George H. > >Hi all, I finally had time to try out these other opamps. >(it was a fail on each one.) >The TLE2142 was a sweet opamp. But I forgot about the bias current. >I've got a variable source impedance (100k ,33k and 10k ohm) and the ~1uA of bias current means 10mV to 100 mV of DC offset. (not acceptable.) Too bad 'cause otherwise it was nice. > >The TLE2142 has an issue running near it's negative rail. It needed the rail to be -3.0 Volts to keep the DC offset below 5mV (When operated from -1.5 V's the offset was ~120mV!) > >The OPA2604 oscillated out of the box and needed a bit of feedback C to tame it. (not a problem.) But it also had a lot of 'issues' (ringy dingies) when driving a coax cable. I mucked around with termination resistors (source and end.) but never got the 'ringies' down to an acceptable level. > >So I figured I'd try over voltaging the opa2134's I've got the supply voltage up to 40V (36V max) and no magic smoke yet. :^) >I tired a few different pieces, and did a bit of turn on/off torture. >The circuit has now been running on the lab bench for several hours. Should I test with some elevated temperatures? >I'm thinking this opamp will be fine. (I'll design for 35 V supplies and worse case it'll only be a tad above 36 volts.) (tad = 400mV in this case) > >George H.
Sounds OK, but it would be better/funner to test the part to failure. Maybe it fails at 41, maybe it fails at 70. -- 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 Jim Thompson July 30, 20132013-07-30
On Tue, 30 Jul 2013 18:27:09 +0000 (UTC), Frank Miles
<fpm@u.washington.edu> wrote:

>On Tue, 30 Jul 2013 11:12:30 -0700, George Herold wrote: > >> On Tuesday, July 30, 2013 12:51:41 PM UTC-4, cassiope wrote: >>> On Tue, 30 Jul 2013 08:11:59 -0700, George Herold wrote: >>> >>> >>> >>> > The OPA2604 oscillated out of the box and needed a bit of feedback C >>> > to >>> >>> > tame it. (not a problem.) But it also had a lot of 'issues' (ringy >>> >>> > dingies) when driving a coax cable. I mucked around with termination >>> >>> > resistors (source and end.) but never got the 'ringies' down to an >>> >>> > acceptable level. >>> >>> >>> >>> Did you try the compensation circuits given in the spec sheet? BB (TI) >>> shows some input RC circuits that help when driving capacitive loads >>> with this amplifier. >> >> No. I'm not sure it was the cable C that was the issue. (Only 3 foot of >> coax and shrinking that to a few inches didn't change a thing.) I did >> put 50 ohms in series. > >Ah - you hadn't mentioned that before. Hmmn - could you describe the ringing >(amplitude, duration, ringing frequency)? > >>> > So I figured I'd try over voltaging the opa2134's I've got the supply > >>> > voltage up to 40V (36V max) and no magic smoke yet. :^) I tired a few >>> >> > different pieces, and did a bit of turn on/off torture. The circuit >>> > has >>> > now been running on the lab bench for several hours. Should I test >>> > with >>> > some elevated temperatures? I'm thinking this opamp will be fine. >>> > (I'll >>> > design for 35 V supplies and worse case it'll only be a tad above 36 >>> > volts.) (tad = 400mV in this case) >>> >>> >>> >>> What kind of reliability do you need? If this is a short-term one-off, >>> you can probably get away with this kind of brinksmanship. If it has >>> to work for others over a longer time period - do everyone a favor and >>> either use a part rated for higher voltage or modify your circuit (e.g. >>> composite amplifier) such that the amplifiers aren't overstressed. >> >> Brinksmanship(?).. It's only 0.4V?.. and that's for worst case. We'll >> sell maybe 100 or so of these over several years. > >I'm pretty conservative when it comes to semiconductor voltages - I'd call >0.4V _less_ than rated voltage was brinksmanship. But I expect my designs >to have "reasonably high" reliability (not medical/life support level). >If you look at failure rate curves with voltage (and I admit I don't recall >seeing any for more modern lower voltage opamps) they are climbing rapidly >and smoothly in the vicinity of the rated voltage. Of course there is a >significant amount of variation. > >> So can you say anything more about the stress? What's the cause? >> I tried hitting the one on the bench with a heat gun, and shorted the >> output. (The case rose to ~100 C. I should see what happens with >> only 36V.) Hey, I'll stick it in a socket. That way if it does fry >> in the future it can be replaced. (opamps are cheap.) > >If your customers are savvy enough to diagnose the problem, and replace >the amplifier without damage to themselves or to the device or to whatever >function they were meant to provide - sure. My users, while often PhDs, >are most often not that electronically savvy. And down-time is expensive.
Have the required signal levels (and load) been mentioned, or just the supply voltages? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 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.