On 05/28/18 13:49, George Herold wrote:> On Sunday, May 27, 2018 at 8:10:21 PM UTC-4, Phil Hobbs wrote: >> On 05/27/18 19:33, bitrex wrote: >>> On 05/27/2018 05:45 PM, Phil Hobbs wrote: >>>> On 05/27/18 16:28, John Larkin wrote: >>>>> On Sun, 27 May 2018 15:09:33 -0400, Phil Hobbs >>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>> >>>>>> Hi, all, >>>>>> >>>>>> I'm generally prejudiced against composite amplifiers (two op amps >>>>>> inside one feedback loop) because they're generally squirrelly, with >>>>>> poor settling performance and weird transient response. >>>>>> >>>>>> On the other hand, my aversion to them means that I don't have as much >>>>>> experience with them as do composite-amp fans. So what do you folks >>>>>> say >>>>>> about them? >>>>>> >>>>>> Orchids? Onions? Actual expertise? >>>>>> >>>>>> Cheers >>>>>> >>>>>> Phil Hobbs >>>>> >>>>> I've only done it a little, in very special cases, but if the intent >>>>> is to apply a slow DC offset correction, and the main amp and the DC >>>>> trim amp don't overlap in frequency response, it seems to work fine. >>>>> >>>>> If you want to make a general -6 dB/octave amp as a composite, the >>>>> risk is probably saturating one of the amps in large-signal/slewing >>>>> cases, or at leasy doing goofy things. A composite that clips clean >>>>> would be a challenge. >>>>> >>>>> A sorta similar case is where a fast signal needs to be DC coupled >>>>> across a big DC offset. A capacitor is the fast path and some slow >>>>> opamp thing does the DC part before the AC path decays. The gains have >>>>> to both be the same, about 1.00 usually, and the frequency responses >>>>> need to be matched, to get clean step response and no ISI. >>>> >>>> Not so easy! >>>> >>>>> >>>>> Tek called this "feed-beside", a brutally fast but ugly signal path, >>>>> and slow stuff in parallel to make it clean. >>>> >>>> Plus a lot a lot of hand work to get them to match. I've benefited >>>> greatly from their labours, but I have no interest in doing that myself! >>>> >>>> What I'm mostly talking about is using a nice quiet accurate amp such >>>> as an ADA4898 plus a faster but less accurate thing such as a THS3091 >>>> or LM6171. The output amp is run at some fixed gain like 10, and the >>>> input amp is run at high enough gain that the combination is stable at >>>> quiescent conditions. >>>> >>>> Other composite amps such as the one you mention or the common case of >>>> using a chopamp to control the offset voltage of some fast-but-ugly >>>> amplifier have a different set of problems. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> And this one from Burr-Brown: >>> >>> <http://www.ti.com/lit/an/sboa002/sboa002.pdf> >> >> Yeah, that's the idea. Problem is that it has horrible transient response. > Have you peaked at the in between opamp signal? > GHIt's generally well behaved until the output amp rails, the reason being that the input amp is the slow one. I've been playing with a CPH3910/ADA4899/THS3091 combination that is starting to look reasonable in the spherical-cow universe. It's a little gain-of-50 amp with about 120 MHz bandwidth, Zin of 10M // <<1pF, and flatband 1-Hz noise of about 1.5 nV. (The capacitance of the connector will dominate.) I seriously doubt it'll work that well in real life. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Composite amps
Started by ●May 27, 2018
Reply by ●May 28, 20182018-05-28
Reply by ●May 28, 20182018-05-28
On 05/28/18 14:07, George Herold wrote:> On Sunday, May 27, 2018 at 8:10:21 PM UTC-4, Phil Hobbs wrote: >> On 05/27/18 19:33, bitrex wrote: >>> On 05/27/2018 05:45 PM, Phil Hobbs wrote: >>>> On 05/27/18 16:28, John Larkin wrote: >>>>> On Sun, 27 May 2018 15:09:33 -0400, Phil Hobbs >>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>> >>>>>> Hi, all, >>>>>> >>>>>> I'm generally prejudiced against composite amplifiers (two op amps >>>>>> inside one feedback loop) because they're generally squirrelly, with >>>>>> poor settling performance and weird transient response. >>>>>> >>>>>> On the other hand, my aversion to them means that I don't have as much >>>>>> experience with them as do composite-amp fans. So what do you folks >>>>>> say >>>>>> about them? >>>>>> >>>>>> Orchids? Onions? Actual expertise? >>>>>> >>>>>> Cheers >>>>>> >>>>>> Phil Hobbs >>>>> >>>>> I've only done it a little, in very special cases, but if the intent >>>>> is to apply a slow DC offset correction, and the main amp and the DC >>>>> trim amp don't overlap in frequency response, it seems to work fine. >>>>> >>>>> If you want to make a general -6 dB/octave amp as a composite, the >>>>> risk is probably saturating one of the amps in large-signal/slewing >>>>> cases, or at leasy doing goofy things. A composite that clips clean >>>>> would be a challenge. >>>>> >>>>> A sorta similar case is where a fast signal needs to be DC coupled >>>>> across a big DC offset. A capacitor is the fast path and some slow >>>>> opamp thing does the DC part before the AC path decays. The gains have >>>>> to both be the same, about 1.00 usually, and the frequency responses >>>>> need to be matched, to get clean step response and no ISI. >>>> >>>> Not so easy! >>>> >>>>> >>>>> Tek called this "feed-beside", a brutally fast but ugly signal path, >>>>> and slow stuff in parallel to make it clean. >>>> >>>> Plus a lot a lot of hand work to get them to match. I've benefited >>>> greatly from their labours, but I have no interest in doing that myself! >>>> >>>> What I'm mostly talking about is using a nice quiet accurate amp such >>>> as an ADA4898 plus a faster but less accurate thing such as a THS3091 >>>> or LM6171. The output amp is run at some fixed gain like 10, and the >>>> input amp is run at high enough gain that the combination is stable at >>>> quiescent conditions. >>>> >>>> Other composite amps such as the one you mention or the common case of >>>> using a chopamp to control the offset voltage of some fast-but-ugly >>>> amplifier have a different set of problems. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> And this one from Burr-Brown: >>> >>> <http://www.ti.com/lit/an/sboa002/sboa002.pdf> >> >> Yeah, that's the idea. Problem is that it has horrible transient response.> Oh you've got some time delay front to back, > maybe feed back around the 1st opamp... > an RC in series? at some intermediate freq./time. > George H. > Inside cooling off, I'm grilling more meat later.Overcast here--has been all weekend. :(> Hey a shoutout to any vet's on Memorial Day. > Thanks!+1 Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●May 28, 20182018-05-28
On 05/27/18 20:05, Phil Hobbs wrote:> On 05/27/18 19:31, bitrex wrote: >> On 05/27/2018 05:45 PM, Phil Hobbs wrote: >>> On 05/27/18 16:28, John Larkin wrote: >>>> On Sun, 27 May 2018 15:09:33 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> Hi, all, >>>>> >>>>> I'm generally prejudiced against composite amplifiers (two op amps >>>>> inside one feedback loop) because they're generally squirrelly, with >>>>> poor settling performance and weird transient response. >>>>> >>>>> On the other hand, my aversion to them means that I don't have as much >>>>> experience with them as do composite-amp fans. So what do you >>>>> folks say >>>>> about them? >>>>> >>>>> Orchids? Onions? Actual expertise? >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> I've only done it a little, in very special cases, but if the intent >>>> is to apply a slow DC offset correction, and the main amp and the DC >>>> trim amp don't overlap in frequency response, it seems to work fine. >>>> >>>> If you want to make a general -6 dB/octave amp as a composite, the >>>> risk is probably saturating one of the amps in large-signal/slewing >>>> cases, or at leasy doing goofy things. A composite that clips clean >>>> would be a challenge. >>>> >>>> A sorta similar case is where a fast signal needs to be DC coupled >>>> across a big DC offset. A capacitor is the fast path and some slow >>>> opamp thing does the DC part before the AC path decays. The gains have >>>> to both be the same, about 1.00 usually, and the frequency responses >>>> need to be matched, to get clean step response and no ISI. >>> >>> Not so easy! >>> >>>> >>>> Tek called this "feed-beside", a brutally fast but ugly signal path, >>>> and slow stuff in parallel to make it clean. >>> >>> Plus a lot a lot of hand work to get them to match. I've benefited >>> greatly from their labours, but I have no interest in doing that myself! >>> >>> What I'm mostly talking about is using a nice quiet accurate amp such >>> as an ADA4898 plus a faster but less accurate thing such as a THS3091 >>> or LM6171. The output amp is run at some fixed gain like 10, and the >>> input amp is run at high enough gain that the combination is stable >>> at quiescent conditions. >>> >>> Other composite amps such as the one you mention or the common case >>> of using a chopamp to control the offset voltage of some >>> fast-but-ugly amplifier have a different set of problems. >>> >>> Cheers >>> >>> Phil Hobbs >> >> This Wireless World article from '74 might be of interest: >> >> <http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1974/Reducing%20Amplifier%20Distortion%20-%20Sandman.pdf> > > > How so?I had a look at the article, and it does have some points of interest, thanks. The author distinguishes between his technique and feedforward, but I'd argue that for circuit purposes it's a species of feedforward, whose basic principle is to sense just the error of an amplifier and apply the appropriate correction to the _output_ and not the _input_. I didn't know that FF was invented by Harold Black. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●May 28, 20182018-05-28
On 05/28/2018 01:28 PM, John Larkin wrote:> On Mon, 28 May 2018 13:09:38 -0400, bitrex <user@example.net> wrote: > >> On 05/28/2018 11:42 AM, John Larkin wrote: >>> On Mon, 28 May 2018 11:35:37 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 05/28/18 11:25, John Larkin wrote: >>>>> On Mon, 28 May 2018 14:59:11 GMT, Steve Wilson <no@spam.com> wrote: >>>>> >>>>>> John Larkin <jjlarkin@highlandtechnology.com> wrote: >>>>>> >>>>>>> Not to change the subject (I'd never do that) but I have made a >>>>>>> compound amp just to shift the power dissipation away from the >>>>>>> front-end diff pair, off to another chip, to avoid nanovolt thermal >>>>>>> hooks. I had to keep the feedback network low impedance to minimize >>>>>>> Johnson noise, which required a lot of feedback current. >>>>>> >>>>>>> https://www.dropbox.com/s/nieqrj2um62pdu5/L700_Shunt_Amp.jpg?raw=1 >>>>>> >>>>>> Not to change the subject, but I have a question. There is another type of >>>>>> amplifier that splits the signal into two paths - a high frequency path for >>>>>> an RF amplifier with poor DC drift and small DC offset capability, and a low >>>>>> frequency path for an amplifier with good DC characteristics and wide offset >>>>>> capability. I thought this was a compound amplifier, and once read an article >>>>>> in the HP Journal that described it. >>>>>> >>>>>> But I can't find the article, and google is no help. Do you know the name of >>>>>> this kind of amplifier? >>>>> >>>>> This is usually called a compound amplifier. Tektronix called >>>>> something similar to this "feed-beside." >>>>> >>>>> There are two ways to do this: >>>>> >>>>> 1. Split the signal with RC or bias tee circuits, amplify the AC and >>>>> DC parts with separate amps, and combine at the output. >>>>> >>>>> 2. Build a compound amp, with optimized AC and DC paths, but treat it >>>>> as a black-box opamp, and close a feedback loop around it. >>>>> >>>>> I don't know of they have specific names. As Phil noted at the start >>>>> here, it's tricky to manage the overlap with precision. >>>>> >>>>> There is an RF power amp configuration that has a high-power amp with >>>>> some distortion, and a paralleled low-power amp with correcting >>>>> distortion behavior. That probably has a name. I think cell towers use >>>>> that. >>>> >>>> Feedforward. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> Not to be confused with predistortion, I guess. >>> >>> https://en.wikipedia.org/wiki/Predistortion >>> >>> I'd play with the compound amp thing, but I need to force myself to do >>> less interesting grunt work. Like revising proposals and replacing >>> faucets. Hard to decide which is less appealing. >>> >> >> What is this "predistortion" discussed in the article but itself a form >> of "regular" negative feedback? >> >> It says "In essence, 'inverse distortion' is introduced into the input >> of the amplifier, thereby cancelling any non-linearity the amplifier >> might have." Yes, that's what negative feedback is. > > Except that predistortion is not negative feedback; all the signals > are going in the same direction. It's hard to do feedback on a GHz > power amp. > >Ah, helpfully the Wiki seems to never mention that it's a feed-forward and not feedback topology.
Reply by ●May 28, 20182018-05-28
On 05/28/2018 03:38 PM, Phil Hobbs wrote:> On 05/28/18 13:49, George Herold wrote: >> On Sunday, May 27, 2018 at 8:10:21 PM UTC-4, Phil Hobbs wrote: >>> On 05/27/18 19:33, bitrex wrote: >>>> On 05/27/2018 05:45 PM, Phil Hobbs wrote: >>>>> On 05/27/18 16:28, John Larkin wrote: >>>>>> On Sun, 27 May 2018 15:09:33 -0400, Phil Hobbs >>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>> >>>>>>> Hi, all, >>>>>>> >>>>>>> I'm generally prejudiced against composite amplifiers (two op amps >>>>>>> inside one feedback loop) because they're generally squirrelly, with >>>>>>> poor settling performance and weird transient response. >>>>>>> >>>>>>> On the other hand, my aversion to them means that I don't have as >>>>>>> much >>>>>>> experience with them as do composite-amp fans. So what do you folks >>>>>>> say >>>>>>> about them? >>>>>>> >>>>>>> Orchids? Onions? Actual expertise? >>>>>>> >>>>>>> Cheers >>>>>>> >>>>>>> Phil Hobbs >>>>>> >>>>>> I've only done it a little, in very special cases, but if the intent >>>>>> is to apply a slow DC offset correction, and the main amp and the DC >>>>>> trim amp don't overlap in frequency response, it seems to work fine. >>>>>> >>>>>> If you want to make a general -6 dB/octave amp as a composite, the >>>>>> risk is probably saturating one of the amps in large-signal/slewing >>>>>> cases, or at leasy doing goofy things. A composite that clips clean >>>>>> would be a challenge. >>>>>> >>>>>> A sorta similar case is where a fast signal needs to be DC coupled >>>>>> across a big DC offset. A capacitor is the fast path and some slow >>>>>> opamp thing does the DC part before the AC path decays. The gains >>>>>> have >>>>>> to both be the same, about 1.00 usually, and the frequency responses >>>>>> need to be matched, to get clean step response and no ISI. >>>>> >>>>> Not so easy! >>>>> >>>>>> >>>>>> Tek called this "feed-beside", a brutally fast but ugly signal path, >>>>>> and slow stuff in parallel to make it clean. >>>>> >>>>> Plus a lot a lot of hand work to get them to match. I've benefited >>>>> greatly from their labours, but I have no interest in doing that >>>>> myself! >>>>> >>>>> What I'm mostly talking about is using a nice quiet accurate amp such >>>>> as an ADA4898 plus a faster but less accurate thing such as a THS3091 >>>>> or LM6171. The output amp is run at some fixed gain like 10, and the >>>>> input amp is run at high enough gain that the combination is stable at >>>>> quiescent conditions. >>>>> >>>>> Other composite amps such as the one you mention or the common case of >>>>> using a chopamp to control the offset voltage of some fast-but-ugly >>>>> amplifier have a different set of problems. >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> And this one from Burr-Brown: >>>> >>>> <http://www.ti.com/lit/an/sboa002/sboa002.pdf> >>> >>> Yeah, that's the idea. Problem is that it has horrible transient >>> response. >> Have you peaked at the in between opamp signal? >> GH > > It's generally well behaved until the output amp rails, the reason being > that the input amp is the slow one. > > I've been playing with a CPH3910/ADA4899/THS3091 combination that is > starting to look reasonable in the spherical-cow universe. It's a > little gain-of-50 amp with about 120 MHz bandwidth, Zin of 10M // <<1pF, > and flatband 1-Hz noise of about 1.5 nV. (The capacitance of the > connector will dominate.) > > I seriously doubt it'll work that well in real life. > > Cheers > > Phil Hobbs > >Have you tried designing a composite-amp oscillator instead? If my theory is correct it should make a wonderful amplifier.
Reply by ●May 28, 20182018-05-28
On 05/28/2018 02:07 PM, George Herold wrote:> On Sunday, May 27, 2018 at 8:10:21 PM UTC-4, Phil Hobbs wrote: >> On 05/27/18 19:33, bitrex wrote: >>> On 05/27/2018 05:45 PM, Phil Hobbs wrote: >>>> On 05/27/18 16:28, John Larkin wrote: >>>>> On Sun, 27 May 2018 15:09:33 -0400, Phil Hobbs >>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>> >>>>>> Hi, all, >>>>>> >>>>>> I'm generally prejudiced against composite amplifiers (two op amps >>>>>> inside one feedback loop) because they're generally squirrelly, with >>>>>> poor settling performance and weird transient response. >>>>>> >>>>>> On the other hand, my aversion to them means that I don't have as much >>>>>> experience with them as do composite-amp fans. So what do you folks >>>>>> say >>>>>> about them? >>>>>> >>>>>> Orchids? Onions? Actual expertise? >>>>>> >>>>>> Cheers >>>>>> >>>>>> Phil Hobbs >>>>> >>>>> I've only done it a little, in very special cases, but if the intent >>>>> is to apply a slow DC offset correction, and the main amp and the DC >>>>> trim amp don't overlap in frequency response, it seems to work fine. >>>>> >>>>> If you want to make a general -6 dB/octave amp as a composite, the >>>>> risk is probably saturating one of the amps in large-signal/slewing >>>>> cases, or at leasy doing goofy things. A composite that clips clean >>>>> would be a challenge. >>>>> >>>>> A sorta similar case is where a fast signal needs to be DC coupled >>>>> across a big DC offset. A capacitor is the fast path and some slow >>>>> opamp thing does the DC part before the AC path decays. The gains have >>>>> to both be the same, about 1.00 usually, and the frequency responses >>>>> need to be matched, to get clean step response and no ISI. >>>> >>>> Not so easy! >>>> >>>>> >>>>> Tek called this "feed-beside", a brutally fast but ugly signal path, >>>>> and slow stuff in parallel to make it clean. >>>> >>>> Plus a lot a lot of hand work to get them to match. I've benefited >>>> greatly from their labours, but I have no interest in doing that myself! >>>> >>>> What I'm mostly talking about is using a nice quiet accurate amp such >>>> as an ADA4898 plus a faster but less accurate thing such as a THS3091 >>>> or LM6171. The output amp is run at some fixed gain like 10, and the >>>> input amp is run at high enough gain that the combination is stable at >>>> quiescent conditions. >>>> >>>> Other composite amps such as the one you mention or the common case of >>>> using a chopamp to control the offset voltage of some fast-but-ugly >>>> amplifier have a different set of problems. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> And this one from Burr-Brown: >>> >>> <http://www.ti.com/lit/an/sboa002/sboa002.pdf> >> >> Yeah, that's the idea. Problem is that it has horrible transient response. >> >> Cheers >> >> Phil Hobbs >> >> -- >> Dr Philip C D Hobbs >> Principal Consultant >> ElectroOptical Innovations LLC / Hobbs ElectroOptics >> Optics, Electro-optics, Photonics, Analog Electronics >> Briarcliff Manor NY 10510 >> >> http://electrooptical.net >> http://hobbs-eo.com > > Oh you've got some time delay front to back, > maybe feed back around the 1st opamp... > an RC in series? at some intermediate freq./time. > George H. > Inside cooling off, I'm grilling more meat later. > Hey a shoutout to any vet's on Memorial Day. > Thanks! > (I should give some buddies a call.) > > GH >I'm taking today to remember my Dad, who passed about two and a half weeks ago just shy of 92. S/Sgt 10th Mountain, served in Italy late 1944 to 1946. Thanks, Dad! And also sort through all his stuff, he was of the generation that never really liked to throw anything away that looked like it would come in handy someday. Sigh...
Reply by ●May 29, 20182018-05-29
On Monday, May 28, 2018 at 7:07:51 PM UTC-4, bitrex wrote:> On 05/28/2018 02:07 PM, George Herold wrote: > > On Sunday, May 27, 2018 at 8:10:21 PM UTC-4, Phil Hobbs wrote: > >> On 05/27/18 19:33, bitrex wrote: > >>> On 05/27/2018 05:45 PM, Phil Hobbs wrote: > >>>> On 05/27/18 16:28, John Larkin wrote: > >>>>> On Sun, 27 May 2018 15:09:33 -0400, Phil Hobbs > >>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: > >>>>> > >>>>>> Hi, all, > >>>>>> > >>>>>> I'm generally prejudiced against composite amplifiers (two op amps > >>>>>> inside one feedback loop) because they're generally squirrelly, with > >>>>>> poor settling performance and weird transient response. > >>>>>> > >>>>>> On the other hand, my aversion to them means that I don't have as much > >>>>>> experience with them as do composite-amp fans. So what do you folks > >>>>>> say > >>>>>> about them? > >>>>>> > >>>>>> Orchids? Onions? Actual expertise? > >>>>>> > >>>>>> Cheers > >>>>>> > >>>>>> Phil Hobbs > >>>>> > >>>>> I've only done it a little, in very special cases, but if the intent > >>>>> is to apply a slow DC offset correction, and the main amp and the DC > >>>>> trim amp don't overlap in frequency response, it seems to work fine. > >>>>> > >>>>> If you want to make a general -6 dB/octave amp as a composite, the > >>>>> risk is probably saturating one of the amps in large-signal/slewing > >>>>> cases, or at leasy doing goofy things. A composite that clips clean > >>>>> would be a challenge. > >>>>> > >>>>> A sorta similar case is where a fast signal needs to be DC coupled > >>>>> across a big DC offset. A capacitor is the fast path and some slow > >>>>> opamp thing does the DC part before the AC path decays. The gains have > >>>>> to both be the same, about 1.00 usually, and the frequency responses > >>>>> need to be matched, to get clean step response and no ISI. > >>>> > >>>> Not so easy! > >>>> > >>>>> > >>>>> Tek called this "feed-beside", a brutally fast but ugly signal path, > >>>>> and slow stuff in parallel to make it clean. > >>>> > >>>> Plus a lot a lot of hand work to get them to match. I've benefited > >>>> greatly from their labours, but I have no interest in doing that myself! > >>>> > >>>> What I'm mostly talking about is using a nice quiet accurate amp such > >>>> as an ADA4898 plus a faster but less accurate thing such as a THS3091 > >>>> or LM6171. The output amp is run at some fixed gain like 10, and the > >>>> input amp is run at high enough gain that the combination is stable at > >>>> quiescent conditions. > >>>> > >>>> Other composite amps such as the one you mention or the common case of > >>>> using a chopamp to control the offset voltage of some fast-but-ugly > >>>> amplifier have a different set of problems. > >>>> > >>>> Cheers > >>>> > >>>> Phil Hobbs > >>> > >>> And this one from Burr-Brown: > >>> > >>> <http://www.ti.com/lit/an/sboa002/sboa002.pdf> > >> > >> Yeah, that's the idea. Problem is that it has horrible transient response. > >> > >> Cheers > >> > >> Phil Hobbs > >> > >> -- > >> Dr Philip C D Hobbs > >> Principal Consultant > >> ElectroOptical Innovations LLC / Hobbs ElectroOptics > >> Optics, Electro-optics, Photonics, Analog Electronics > >> Briarcliff Manor NY 10510 > >> > >> http://electrooptical.net > >> http://hobbs-eo.com > > > > Oh you've got some time delay front to back, > > maybe feed back around the 1st opamp... > > an RC in series? at some intermediate freq./time. > > George H. > > Inside cooling off, I'm grilling more meat later. > > Hey a shoutout to any vet's on Memorial Day. > > Thanks! > > (I should give some buddies a call.) > > > > GH > > > > I'm taking today to remember my Dad, who passed about two and a half > weeks ago just shy of 92. S/Sgt 10th Mountain, served in Italy late 1944 > to 1946. > > Thanks, Dad! > > And also sort through all his stuff, he was of the generation that never > really liked to throw anything away that looked like it would come in > handy someday. Sigh...I'm sorry for your loss. My dad was part of the 'greatest' generation too, but he passed away in his 70's. Years ago. He served in the South Pacific. George H.
Reply by ●May 29, 20182018-05-29
On 05/29/2018 08:53 AM, George Herold wrote:> On Monday, May 28, 2018 at 7:07:51 PM UTC-4, bitrex wrote: >> On 05/28/2018 02:07 PM, George Herold wrote: >>> On Sunday, May 27, 2018 at 8:10:21 PM UTC-4, Phil Hobbs wrote: >>>> On 05/27/18 19:33, bitrex wrote: >>>>> On 05/27/2018 05:45 PM, Phil Hobbs wrote: >>>>>> On 05/27/18 16:28, John Larkin wrote: >>>>>>> On Sun, 27 May 2018 15:09:33 -0400, Phil Hobbs >>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>>> >>>>>>>> Hi, all, >>>>>>>> >>>>>>>> I'm generally prejudiced against composite amplifiers (two op amps >>>>>>>> inside one feedback loop) because they're generally squirrelly, with >>>>>>>> poor settling performance and weird transient response. >>>>>>>> >>>>>>>> On the other hand, my aversion to them means that I don't have as much >>>>>>>> experience with them as do composite-amp fans. So what do you folks >>>>>>>> say >>>>>>>> about them? >>>>>>>> >>>>>>>> Orchids? Onions? Actual expertise? >>>>>>>> >>>>>>>> Cheers >>>>>>>> >>>>>>>> Phil Hobbs >>>>>>> >>>>>>> I've only done it a little, in very special cases, but if the intent >>>>>>> is to apply a slow DC offset correction, and the main amp and the DC >>>>>>> trim amp don't overlap in frequency response, it seems to work fine. >>>>>>> >>>>>>> If you want to make a general -6 dB/octave amp as a composite, the >>>>>>> risk is probably saturating one of the amps in large-signal/slewing >>>>>>> cases, or at leasy doing goofy things. A composite that clips clean >>>>>>> would be a challenge. >>>>>>> >>>>>>> A sorta similar case is where a fast signal needs to be DC coupled >>>>>>> across a big DC offset. A capacitor is the fast path and some slow >>>>>>> opamp thing does the DC part before the AC path decays. The gains have >>>>>>> to both be the same, about 1.00 usually, and the frequency responses >>>>>>> need to be matched, to get clean step response and no ISI. >>>>>> >>>>>> Not so easy! >>>>>> >>>>>>> >>>>>>> Tek called this "feed-beside", a brutally fast but ugly signal path, >>>>>>> and slow stuff in parallel to make it clean. >>>>>> >>>>>> Plus a lot a lot of hand work to get them to match. I've benefited >>>>>> greatly from their labours, but I have no interest in doing that myself! >>>>>> >>>>>> What I'm mostly talking about is using a nice quiet accurate amp such >>>>>> as an ADA4898 plus a faster but less accurate thing such as a THS3091 >>>>>> or LM6171. The output amp is run at some fixed gain like 10, and the >>>>>> input amp is run at high enough gain that the combination is stable at >>>>>> quiescent conditions. >>>>>> >>>>>> Other composite amps such as the one you mention or the common case of >>>>>> using a chopamp to control the offset voltage of some fast-but-ugly >>>>>> amplifier have a different set of problems. >>>>>> >>>>>> Cheers >>>>>> >>>>>> Phil Hobbs >>>>> >>>>> And this one from Burr-Brown: >>>>> >>>>> <http://www.ti.com/lit/an/sboa002/sboa002.pdf> >>>> >>>> Yeah, that's the idea. Problem is that it has horrible transient response. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>>> >>>> -- >>>> Dr Philip C D Hobbs >>>> Principal Consultant >>>> ElectroOptical Innovations LLC / Hobbs ElectroOptics >>>> Optics, Electro-optics, Photonics, Analog Electronics >>>> Briarcliff Manor NY 10510 >>>> >>>> http://electrooptical.net >>>> http://hobbs-eo.com >>> >>> Oh you've got some time delay front to back, >>> maybe feed back around the 1st opamp... >>> an RC in series? at some intermediate freq./time. >>> George H. >>> Inside cooling off, I'm grilling more meat later. >>> Hey a shoutout to any vet's on Memorial Day. >>> Thanks! >>> (I should give some buddies a call.) >>> >>> GH >>> >> >> I'm taking today to remember my Dad, who passed about two and a half >> weeks ago just shy of 92. S/Sgt 10th Mountain, served in Italy late 1944 >> to 1946. >> >> Thanks, Dad! >> >> And also sort through all his stuff, he was of the generation that never >> really liked to throw anything away that looked like it would come in >> handy someday. Sigh... > > I'm sorry for your loss. My dad was part of the 'greatest' generation too, > but he passed away in his 70's. Years ago. He served in the South Pacific. > > George H. >I'm the youngest of four kids, I got more time with him than most guys whose fathers were in their early 50s when they were born. He remained pretty much independent until he died but required a few hours a week of help from me and a nurse the past few years that I was glad to assist with, we were still going out for lunch about once a week until last month. About a week before he died he'd got some test results back that didn't look too good. He was rarely a pessimist, about the closest he came was that day when he looked very tired and said that he missed his friends, all the people who he used to know who by now were all gone. I could understand that, one son who visits regularly is nice but can hardly make up for all the rest. He became very ill the next week and passed away about 48 hours after arrival at the hospital, just enough time for the rest of the family to make it to be there with us. It went about as "well" as it could and at that age and I'd known for quite a while the day would come sooner or later, but I'm still thinking it's him when the phone rings. It's all still very strange. :)
Reply by ●May 29, 20182018-05-29
On 05/29/2018 08:53 AM, George Herold wrote:> On Monday, May 28, 2018 at 7:07:51 PM UTC-4, bitrex wrote: >> On 05/28/2018 02:07 PM, George Herold wrote: >>> On Sunday, May 27, 2018 at 8:10:21 PM UTC-4, Phil Hobbs wrote: >>>> On 05/27/18 19:33, bitrex wrote: >>>>> On 05/27/2018 05:45 PM, Phil Hobbs wrote: >>>>>> On 05/27/18 16:28, John Larkin wrote: >>>>>>> On Sun, 27 May 2018 15:09:33 -0400, Phil Hobbs >>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>>> >>>>>>>> Hi, all, >>>>>>>> >>>>>>>> I'm generally prejudiced against composite amplifiers (two op amps >>>>>>>> inside one feedback loop) because they're generally squirrelly, with >>>>>>>> poor settling performance and weird transient response. >>>>>>>> >>>>>>>> On the other hand, my aversion to them means that I don't have as much >>>>>>>> experience with them as do composite-amp fans. So what do you folks >>>>>>>> say >>>>>>>> about them? >>>>>>>> >>>>>>>> Orchids? Onions? Actual expertise? >>>>>>>> >>>>>>>> Cheers >>>>>>>> >>>>>>>> Phil Hobbs >>>>>>> >>>>>>> I've only done it a little, in very special cases, but if the intent >>>>>>> is to apply a slow DC offset correction, and the main amp and the DC >>>>>>> trim amp don't overlap in frequency response, it seems to work fine. >>>>>>> >>>>>>> If you want to make a general -6 dB/octave amp as a composite, the >>>>>>> risk is probably saturating one of the amps in large-signal/slewing >>>>>>> cases, or at leasy doing goofy things. A composite that clips clean >>>>>>> would be a challenge. >>>>>>> >>>>>>> A sorta similar case is where a fast signal needs to be DC coupled >>>>>>> across a big DC offset. A capacitor is the fast path and some slow >>>>>>> opamp thing does the DC part before the AC path decays. The gains have >>>>>>> to both be the same, about 1.00 usually, and the frequency responses >>>>>>> need to be matched, to get clean step response and no ISI. >>>>>> >>>>>> Not so easy! >>>>>> >>>>>>> >>>>>>> Tek called this "feed-beside", a brutally fast but ugly signal path, >>>>>>> and slow stuff in parallel to make it clean. >>>>>> >>>>>> Plus a lot a lot of hand work to get them to match. I've benefited >>>>>> greatly from their labours, but I have no interest in doing that myself! >>>>>> >>>>>> What I'm mostly talking about is using a nice quiet accurate amp such >>>>>> as an ADA4898 plus a faster but less accurate thing such as a THS3091 >>>>>> or LM6171. The output amp is run at some fixed gain like 10, and the >>>>>> input amp is run at high enough gain that the combination is stable at >>>>>> quiescent conditions. >>>>>> >>>>>> Other composite amps such as the one you mention or the common case of >>>>>> using a chopamp to control the offset voltage of some fast-but-ugly >>>>>> amplifier have a different set of problems. >>>>>> >>>>>> Cheers >>>>>> >>>>>> Phil Hobbs >>>>> >>>>> And this one from Burr-Brown: >>>>> >>>>> <http://www.ti.com/lit/an/sboa002/sboa002.pdf> >>>> >>>> Yeah, that's the idea. Problem is that it has horrible transient response. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>>> >>>> -- >>>> Dr Philip C D Hobbs >>>> Principal Consultant >>>> ElectroOptical Innovations LLC / Hobbs ElectroOptics >>>> Optics, Electro-optics, Photonics, Analog Electronics >>>> Briarcliff Manor NY 10510 >>>> >>>> http://electrooptical.net >>>> http://hobbs-eo.com >>> >>> Oh you've got some time delay front to back, >>> maybe feed back around the 1st opamp... >>> an RC in series? at some intermediate freq./time. >>> George H. >>> Inside cooling off, I'm grilling more meat later. >>> Hey a shoutout to any vet's on Memorial Day. >>> Thanks! >>> (I should give some buddies a call.) >>> >>> GH >>> >> >> I'm taking today to remember my Dad, who passed about two and a half >> weeks ago just shy of 92. S/Sgt 10th Mountain, served in Italy late 1944 >> to 1946. >> >> Thanks, Dad! >> >> And also sort through all his stuff, he was of the generation that never >> really liked to throw anything away that looked like it would come in >> handy someday. Sigh... > > I'm sorry for your loss. My dad was part of the 'greatest' generation too, > but he passed away in his 70's. Years ago. He served in the South Pacific. > > George H. >And thank you! Dad was kind of hit-or-miss as a father (like most fathers I suppose) but it was remarkable hearing the stories about the time he came from which was both so different and so much the same as th time I grew up in, I am happy to say he was a man I was proud to have had a chance to know.
Reply by ●May 29, 20182018-05-29
On Tuesday, May 29, 2018 at 10:26:04 AM UTC-4, bitrex wrote:> On 05/29/2018 08:53 AM, George Herold wrote: > > On Monday, May 28, 2018 at 7:07:51 PM UTC-4, bitrex wrote: > >> On 05/28/2018 02:07 PM, George Herold wrote: > >>> On Sunday, May 27, 2018 at 8:10:21 PM UTC-4, Phil Hobbs wrote: > >>>> On 05/27/18 19:33, bitrex wrote: > >>>>> On 05/27/2018 05:45 PM, Phil Hobbs wrote: > >>>>>> On 05/27/18 16:28, John Larkin wrote: > >>>>>>> On Sun, 27 May 2018 15:09:33 -0400, Phil Hobbs > >>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: > >>>>>>> > >>>>>>>> Hi, all, > >>>>>>>> > >>>>>>>> I'm generally prejudiced against composite amplifiers (two op amps > >>>>>>>> inside one feedback loop) because they're generally squirrelly, with > >>>>>>>> poor settling performance and weird transient response. > >>>>>>>> > >>>>>>>> On the other hand, my aversion to them means that I don't have as much > >>>>>>>> experience with them as do composite-amp fans. So what do you folks > >>>>>>>> say > >>>>>>>> about them? > >>>>>>>> > >>>>>>>> Orchids? Onions? Actual expertise? > >>>>>>>> > >>>>>>>> Cheers > >>>>>>>> > >>>>>>>> Phil Hobbs > >>>>>>> > >>>>>>> I've only done it a little, in very special cases, but if the intent > >>>>>>> is to apply a slow DC offset correction, and the main amp and the DC > >>>>>>> trim amp don't overlap in frequency response, it seems to work fine. > >>>>>>> > >>>>>>> If you want to make a general -6 dB/octave amp as a composite, the > >>>>>>> risk is probably saturating one of the amps in large-signal/slewing > >>>>>>> cases, or at leasy doing goofy things. A composite that clips clean > >>>>>>> would be a challenge. > >>>>>>> > >>>>>>> A sorta similar case is where a fast signal needs to be DC coupled > >>>>>>> across a big DC offset. A capacitor is the fast path and some slow > >>>>>>> opamp thing does the DC part before the AC path decays. The gains have > >>>>>>> to both be the same, about 1.00 usually, and the frequency responses > >>>>>>> need to be matched, to get clean step response and no ISI. > >>>>>> > >>>>>> Not so easy! > >>>>>> > >>>>>>> > >>>>>>> Tek called this "feed-beside", a brutally fast but ugly signal path, > >>>>>>> and slow stuff in parallel to make it clean. > >>>>>> > >>>>>> Plus a lot a lot of hand work to get them to match. I've benefited > >>>>>> greatly from their labours, but I have no interest in doing that myself! > >>>>>> > >>>>>> What I'm mostly talking about is using a nice quiet accurate amp such > >>>>>> as an ADA4898 plus a faster but less accurate thing such as a THS3091 > >>>>>> or LM6171. The output amp is run at some fixed gain like 10, and the > >>>>>> input amp is run at high enough gain that the combination is stable at > >>>>>> quiescent conditions. > >>>>>> > >>>>>> Other composite amps such as the one you mention or the common case of > >>>>>> using a chopamp to control the offset voltage of some fast-but-ugly > >>>>>> amplifier have a different set of problems. > >>>>>> > >>>>>> Cheers > >>>>>> > >>>>>> Phil Hobbs > >>>>> > >>>>> And this one from Burr-Brown: > >>>>> > >>>>> <http://www.ti.com/lit/an/sboa002/sboa002.pdf> > >>>> > >>>> Yeah, that's the idea. Problem is that it has horrible transient response. > >>>> > >>>> Cheers > >>>> > >>>> Phil Hobbs > >>>> > >>>> -- > >>>> Dr Philip C D Hobbs > >>>> Principal Consultant > >>>> ElectroOptical Innovations LLC / Hobbs ElectroOptics > >>>> Optics, Electro-optics, Photonics, Analog Electronics > >>>> Briarcliff Manor NY 10510 > >>>> > >>>> http://electrooptical.net > >>>> http://hobbs-eo.com > >>> > >>> Oh you've got some time delay front to back, > >>> maybe feed back around the 1st opamp... > >>> an RC in series? at some intermediate freq./time. > >>> George H. > >>> Inside cooling off, I'm grilling more meat later. > >>> Hey a shoutout to any vet's on Memorial Day. > >>> Thanks! > >>> (I should give some buddies a call.) > >>> > >>> GH > >>> > >> > >> I'm taking today to remember my Dad, who passed about two and a half > >> weeks ago just shy of 92. S/Sgt 10th Mountain, served in Italy late 1944 > >> to 1946. > >> > >> Thanks, Dad! > >> > >> And also sort through all his stuff, he was of the generation that never > >> really liked to throw anything away that looked like it would come in > >> handy someday. Sigh... > > > > I'm sorry for your loss. My dad was part of the 'greatest' generation too, > > but he passed away in his 70's. Years ago. He served in the South Pacific. > > > > George H. > > > > And thank you! Dad was kind of hit-or-miss as a father (like most > fathers I suppose) but it was remarkable hearing the stories about the > time he came from which was both so different and so much the same as th > time I grew up in, I am happy to say he was a man I was proud to have > had a chance to know.Sure, my dad died one night, massive heart attack, he was set to go hunting the next day with buddies. It was totally unexpected from my point of view, but we learned after the fact (from his girlfriend) that he wasn't taking his high blood pressure meds. Some type of advanced warning is mostly a good thing, let's you sorta prepare... emotionally. George H.
