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Difference Amp.

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  Difference Amp. George Herold <gherold@teachspin.com> - 2017-02-07 12:56 -0800
    Re: Difference Amp. Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-07 16:40 -0500
      Re: Difference Amp. gghero27@gmail.com - 2017-02-07 17:47 -0800
        Re: Difference Amp. Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-08 11:45 -0500
          Re: Difference Amp. George Herold <gherold@teachspin.com> - 2017-02-08 10:58 -0800
            Re: Difference Amp. Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-08 12:20 -0700
              Re: Difference Amp. Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-08 12:34 -0700
                Re: Difference Amp. Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-08 16:09 -0500
                  Re: Difference Amp. Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-08 14:12 -0700
                    Re: Difference Amp. Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-08 16:15 -0500
                      Re: Difference Amp. Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-08 14:21 -0700
                        Re: Difference Amp. George Herold <gherold@teachspin.com> - 2017-02-08 16:28 -0800
            Re: Difference Amp. Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-08 16:08 -0500
      Re: Difference Amp. gghero27@gmail.com - 2017-02-07 17:47 -0800
    Re: Difference Amp. sdy <sdeyoreo@hotmail.com> - 2017-02-07 16:20 -0800
      Re: Difference Amp. gghero27@gmail.com - 2017-02-07 17:50 -0800
        Re: Difference Amp. John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-08 12:45 -0800
    Re: Difference Amp. John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-07 17:22 -0800
      Re: Difference Amp. Winfield Hill <hill@rowland.harvard.edu> - 2017-02-07 17:40 -0800
        Re: Difference Amp. Robert Latest <boblatest@yahoo.com> - 2017-02-08 18:10 +0000
          Re: Difference Amp. Winfield Hill <hill@rowland.harvard.edu> - 2017-02-08 12:06 -0800
            Re: Difference Amp. Robert Latest <boblatest@yahoo.com> - 2017-02-09 17:55 +0000
    Re: Difference Amp. Kamen Lilov <kamenl@gmail.com> - 2017-02-08 11:25 -0800
      Re: Difference Amp. George Herold <gherold@teachspin.com> - 2017-02-08 12:41 -0800
        Re: Difference Amp. George Herold <gherold@teachspin.com> - 2017-02-08 12:47 -0800
      Re: Difference Amp. krw@notreal.com - 2017-02-08 20:43 -0500

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#446685 — Difference Amp.

OK first a failure at Digikey.  I went searching for difference amps, 
but they are listed in many different places.  (So it's hard to look at 
them all at once.  (See table 5.7 pg 353 in AoE3)) Most are listed as 
Differential amps w/o differential outputs.  But the LT1191 is 
under programmable gain, and INA134 is under linear-amps-audio.  
(A section I'm going to have to troll a bit more... lotsa potential 
power op-amps, that I don't know about.)  

Anyway, I need a few difference amps.  The ina132 is a reasonable example,
http://www.ti.com/lit/ds/symlink/ina132.pdf  
An opamp with laser trimmed resistors already in place.  

I've been using an instrument amp, but it's overkill.  
I've never used a difference amp.  
First question, do you expect these to go away in the future?  
(say 10 years)  
Hmm that might be my only question.  Would you use these instead 
of an opamp and 0.1% R's?   

Thanks 

George H. 

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#446689

On 02/07/2017 03:56 PM, George Herold wrote:
> OK first a failure at Digikey.  I went searching for difference amps,
> but they are listed in many different places.  (So it's hard to look at
> them all at once.  (See table 5.7 pg 353 in AoE3)) Most are listed as
> Differential amps w/o differential outputs.  But the LT1191 is
> under programmable gain, and INA134 is under linear-amps-audio.
> (A section I'm going to have to troll a bit more... lotsa potential
> power op-amps, that I don't know about.)
>
> Anyway, I need a few difference amps.  The ina132 is a reasonable example,
> http://www.ti.com/lit/ds/symlink/ina132.pdf
> An opamp with laser trimmed resistors already in place.
>
> I've been using an instrument amp, but it's overkill.
> I've never used a difference amp.
> First question, do you expect these to go away in the future?
> (say 10 years)
> Hmm that might be my only question.  Would you use these instead
> of an opamp and 0.1% R's?

I've used them in various test jigs and small instruments (usually the 
PMI/AD AMP03 because I had a bunch of them).  They're very convenient 
and the resistors track well, which is one advantage, but I'm usually 
using them for strange stuff such as very accurate x1/x2 amps.

One problem is that you have to drive all three inputs from super low-Z 
sources or you'll ruin the CMR.

Cheers

Phil Hobbs

(Just getting up from a bout of pneumonia due to a virus I brought back 
from vacation.) :(



-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

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#446721

On Tuesday, February 7, 2017 at 4:40:24 PM UTC-5, Phil Hobbs wrote:
> On 02/07/2017 03:56 PM, George Herold wrote:
> > OK first a failure at Digikey.  I went searching for difference amps,
> > but they are listed in many different places.  (So it's hard to look at
> > them all at once.  (See table 5.7 pg 353 in AoE3)) Most are listed as
> > Differential amps w/o differential outputs.  But the LT1191 is
> > under programmable gain, and INA134 is under linear-amps-audio.
> > (A section I'm going to have to troll a bit more... lotsa potential
> > power op-amps, that I don't know about.)
> >
> > Anyway, I need a few difference amps.  The ina132 is a reasonable example,
> > http://www.ti.com/lit/ds/symlink/ina132.pdf
> > An opamp with laser trimmed resistors already in place.
> >
> > I've been using an instrument amp, but it's overkill.
> > I've never used a difference amp.
> > First question, do you expect these to go away in the future?
> > (say 10 years)
> > Hmm that might be my only question.  Would you use these instead
> > of an opamp and 0.1% R's?
> 
> I've used them in various test jigs and small instruments (usually the 
> PMI/AD AMP03 because I had a bunch of them).  They're very convenient 
> and the resistors track well, which is one advantage, but I'm usually 
> using them for strange stuff such as very accurate x1/x2 amps.
> 
> One problem is that you have to drive all three inputs from super low-Z 
> sources or you'll ruin the CMR.
Yeah, this is just inside a slow analog control loop, so opamps or such
driving all the R's.  I don't care too much about CMR... (I think..
noise and interference can tricky,)
I'm adding and subtracting analog signals, I was thinking 
how much easier it would be with an Int amp, rather than
two opamps to sum and then invert.  And then why not 
a difference amp.  (which I only learned about from AoE3.)

Then again I've seen analog bits go away.  
(I've got a few UAF42?? (burr brown SV filter IC)
in my parts box... went away just when I built my first 
SV filter...(did I mention I often feel like I live on 
the trailing edge of technology?)  We can save a little 
by buying Int amp's in bulk... they will have a longer lifetime 
than Diff amps.

Then again again, I can see all sorts of nice ways to use, 
opamps w/R's, saves space... there're many vendors.

George H. 


> 
> Cheers
> 
> Phil Hobbs
> 
> (Just getting up from a bout of pneumonia due to a virus I brought back 
> from vacation.) :(
> 
> 
> 
> -- 
> Dr Philip C D Hobbs
> Principal Consultant
> ElectroOptical Innovations LLC
> Optics, Electro-optics, Photonics, Analog Electronics
> 
> 160 North State Road #203
> Briarcliff Manor NY 10510
> 
> hobbs at electrooptical dot net
> http://electrooptical.net

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#446789

On 02/07/2017 08:47 PM, gghero27@gmail.com wrote:
> On Tuesday, February 7, 2017 at 4:40:24 PM UTC-5, Phil Hobbs wrote:
>> On 02/07/2017 03:56 PM, George Herold wrote:
>>> OK first a failure at Digikey.  I went searching for difference amps,
>>> but they are listed in many different places.  (So it's hard to look at
>>> them all at once.  (See table 5.7 pg 353 in AoE3)) Most are listed as
>>> Differential amps w/o differential outputs.  But the LT1191 is
>>> under programmable gain, and INA134 is under linear-amps-audio.
>>> (A section I'm going to have to troll a bit more... lotsa potential
>>> power op-amps, that I don't know about.)
>>>
>>> Anyway, I need a few difference amps.  The ina132 is a reasonable example,
>>> http://www.ti.com/lit/ds/symlink/ina132.pdf
>>> An opamp with laser trimmed resistors already in place.
>>>
>>> I've been using an instrument amp, but it's overkill.
>>> I've never used a difference amp.
>>> First question, do you expect these to go away in the future?
>>> (say 10 years)
>>> Hmm that might be my only question.  Would you use these instead
>>> of an opamp and 0.1% R's?
>>
>> I've used them in various test jigs and small instruments (usually the
>> PMI/AD AMP03 because I had a bunch of them).  They're very convenient
>> and the resistors track well, which is one advantage, but I'm usually
>> using them for strange stuff such as very accurate x1/x2 amps.
>>
>> One problem is that you have to drive all three inputs from super low-Z
>> sources or you'll ruin the CMR.
> Yeah, this is just inside a slow analog control loop, so opamps or such
> driving all the R's.  I don't care too much about CMR... (I think..
> noise and interference can tricky,)
> I'm adding and subtracting analog signals, I was thinking
> how much easier it would be with an Int amp, rather than
> two opamps to sum and then invert.  And then why not
> a difference amp.  (which I only learned about from AoE3.)

Seems like an expensive way to save four ordinary resistors if you don't 
care about CMR.  The AMP03's DC CMR is 100 dB typical, which is pretty 
good for a part that old.

Cheers

Phil Hobbs


-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

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#446832

On Wednesday, February 8, 2017 at 11:44:23 AM UTC-5, Phil Hobbs wrote:
> On 02/07/2017 08:47 PM, gghero27@gmail.com wrote:
> > On Tuesday, February 7, 2017 at 4:40:24 PM UTC-5, Phil Hobbs wrote:
> >> On 02/07/2017 03:56 PM, George Herold wrote:
> >>> OK first a failure at Digikey.  I went searching for difference amps,
> >>> but they are listed in many different places.  (So it's hard to look at
> >>> them all at once.  (See table 5.7 pg 353 in AoE3)) Most are listed as
> >>> Differential amps w/o differential outputs.  But the LT1191 is
> >>> under programmable gain, and INA134 is under linear-amps-audio.
> >>> (A section I'm going to have to troll a bit more... lotsa potential
> >>> power op-amps, that I don't know about.)
> >>>
> >>> Anyway, I need a few difference amps.  The ina132 is a reasonable example,
> >>> http://www.ti.com/lit/ds/symlink/ina132.pdf
> >>> An opamp with laser trimmed resistors already in place.
> >>>
> >>> I've been using an instrument amp, but it's overkill.
> >>> I've never used a difference amp.
> >>> First question, do you expect these to go away in the future?
> >>> (say 10 years)
> >>> Hmm that might be my only question.  Would you use these instead
> >>> of an opamp and 0.1% R's?
> >>
> >> I've used them in various test jigs and small instruments (usually the
> >> PMI/AD AMP03 because I had a bunch of them).  They're very convenient
> >> and the resistors track well, which is one advantage, but I'm usually
> >> using them for strange stuff such as very accurate x1/x2 amps.
> >>
> >> One problem is that you have to drive all three inputs from super low-Z
> >> sources or you'll ruin the CMR.
> > Yeah, this is just inside a slow analog control loop, so opamps or such
> > driving all the R's.  I don't care too much about CMR... (I think..
> > noise and interference can tricky,)
> > I'm adding and subtracting analog signals, I was thinking
> > how much easier it would be with an Int amp, rather than
> > two opamps to sum and then invert.  And then why not
> > a difference amp.  (which I only learned about from AoE3.)
> 
> Seems like an expensive way to save four ordinary resistors if you don't 
> care about CMR.  The AMP03's DC CMR is 100 dB typical, which is pretty 
> good for a part that old.

Hmm maybe.  I was replacing an Int amp, so it's cheaper than that. 
I do care about the gain accuracy...
I'm taking the difference between a set point and temperature, to make 
an error signal.  (As well as other even less critical stuff.)

OK, I'll stick with the Int amp, that is in stock and make the other 
diff amp from an opamp and R's. 

Say, Here's a somewhat related question.  I'll often use an inverting amp
to make input connection to the outside world.  (With input R's ranging from 
1 k to 1 Meg ohm.)  I figure the opamp has some input protection and adding more 
series R is only going to make it better.  Is that kosher?  
(It's never caused me any problems yet.)  

George H.      

> 
> Cheers
> 
> Phil Hobbs
> 
> 
> -- 
> Dr Philip C D Hobbs
> Principal Consultant
> ElectroOptical Innovations LLC
> Optics, Electro-optics, Photonics, Analog Electronics
> 
> 160 North State Road #203
> Briarcliff Manor NY 10510
> 
> hobbs at electrooptical dot net
> http://electrooptical.net

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#446837

On Wed, 8 Feb 2017 10:58:57 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

[snip
 
>
>Say, Here's a somewhat related question.  I'll often use an inverting amp
>to make input connection to the outside world.  (With input R's ranging from 
>1 k to 1 Meg ohm.)  I figure the opamp has some input protection and adding more 
>series R is only going to make it better.  Is that kosher?  
>(It's never caused me any problems yet.)  
>
>George H.      
>
>> 
[snip]

Diodes from summing junction to ground will make it very robust.

(May need small resistance in series with each for stability.)
		
                                        ...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.

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#446841

On Wed, 08 Feb 2017 12:20:33 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Wed, 8 Feb 2017 10:58:57 -0800 (PST), George Herold
><gherold@teachspin.com> wrote:
>
>[snip
> 
>>
>>Say, Here's a somewhat related question.  I'll often use an inverting amp
>>to make input connection to the outside world.  (With input R's ranging from 
>>1 k to 1 Meg ohm.)  I figure the opamp has some input protection and adding more 
>>series R is only going to make it better.  Is that kosher?  
>>(It's never caused me any problems yet.)  
>>
>>George H.      
>>
>>> 
>[snip]
>
>Diodes from summing junction to ground will make it very robust.

Anti-parallel.  Is that called back-to-back or belly-to-belly ?:-}

>
>(May need small resistance in series with each for stability.)
>		
>                                        ...Jim Thompson
		
                                        ...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.

[toc] | [prev] | [next] | [standalone]

#446859

On 02/08/2017 02:34 PM, Jim Thompson wrote:
> On Wed, 08 Feb 2017 12:20:33 -0700, Jim Thompson
> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>
>> On Wed, 8 Feb 2017 10:58:57 -0800 (PST), George Herold
>> <gherold@teachspin.com> wrote:
>>
>> [snip
>>
>>>
>>> Say, Here's a somewhat related question.  I'll often use an inverting amp
>>> to make input connection to the outside world.  (With input R's ranging from
>>> 1 k to 1 Meg ohm.)  I figure the opamp has some input protection and adding more
>>> series R is only going to make it better.  Is that kosher?
>>> (It's never caused me any problems yet.)
>>>
>>> George H.
>>>
>>>>
>> [snip]
>>
>> Diodes from summing junction to ground will make it very robust.
>
> Anti-parallel.  Is that called back-to-back or belly-to-belly ?:-}
>
Yup.  Back-to-back is inverse series, as in "back-to-back zeners".

Cheers

Phil Hobbs


-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

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#446862

On Wed, 8 Feb 2017 16:09:14 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 02/08/2017 02:34 PM, Jim Thompson wrote:
>> On Wed, 08 Feb 2017 12:20:33 -0700, Jim Thompson
>> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>>
>>> On Wed, 8 Feb 2017 10:58:57 -0800 (PST), George Herold
>>> <gherold@teachspin.com> wrote:
>>>
>>> [snip
>>>
>>>>
>>>> Say, Here's a somewhat related question.  I'll often use an inverting amp
>>>> to make input connection to the outside world.  (With input R's ranging from
>>>> 1 k to 1 Meg ohm.)  I figure the opamp has some input protection and adding more
>>>> series R is only going to make it better.  Is that kosher?
>>>> (It's never caused me any problems yet.)
>>>>
>>>> George H.
>>>>
>>>>>
>>> [snip]
>>>
>>> Diodes from summing junction to ground will make it very robust.
>>
>> Anti-parallel.  Is that called back-to-back or belly-to-belly ?:-}
>>
>Yup.  Back-to-back is inverse series, as in "back-to-back zeners".
>
>Cheers
>
>Phil Hobbs

So belly-to-belly anti-parallel ?:-}
		
                                        ...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.

[toc] | [prev] | [next] | [standalone]

#446865

On 02/08/2017 04:12 PM, Jim Thompson wrote:
> On Wed, 8 Feb 2017 16:09:14 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> On 02/08/2017 02:34 PM, Jim Thompson wrote:
>>> On Wed, 08 Feb 2017 12:20:33 -0700, Jim Thompson
>>> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>>>
>>>> On Wed, 8 Feb 2017 10:58:57 -0800 (PST), George Herold
>>>> <gherold@teachspin.com> wrote:
>>>>
>>>> [snip
>>>>
>>>>>
>>>>> Say, Here's a somewhat related question.  I'll often use an inverting amp
>>>>> to make input connection to the outside world.  (With input R's ranging from
>>>>> 1 k to 1 Meg ohm.)  I figure the opamp has some input protection and adding more
>>>>> series R is only going to make it better.  Is that kosher?
>>>>> (It's never caused me any problems yet.)
>>>>>
>>>>> George H.
>>>>>
>>>>>>
>>>> [snip]
>>>>
>>>> Diodes from summing junction to ground will make it very robust.
>>>
>>> Anti-parallel.  Is that called back-to-back or belly-to-belly ?:-}
>>>
>> Yup.  Back-to-back is inverse series, as in "back-to-back zeners".
>>
>> Cheers
>>
>> Phil Hobbs
>
> So belly-to-belly anti-parallel ?:-}
> 		
>                                         ...Jim Thompson
>
This is a family show. (For values of "family" corresponding to dates 
before 1965.)

Cheers

Phil Hobbs


-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

[toc] | [prev] | [next] | [standalone]

#446867

On Wed, 8 Feb 2017 16:15:10 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 02/08/2017 04:12 PM, Jim Thompson wrote:
>> On Wed, 8 Feb 2017 16:09:14 -0500, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>
>>> On 02/08/2017 02:34 PM, Jim Thompson wrote:
>>>> On Wed, 08 Feb 2017 12:20:33 -0700, Jim Thompson
>>>> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>>>>
>>>>> On Wed, 8 Feb 2017 10:58:57 -0800 (PST), George Herold
>>>>> <gherold@teachspin.com> wrote:
>>>>>
>>>>> [snip
>>>>>
>>>>>>
>>>>>> Say, Here's a somewhat related question.  I'll often use an inverting amp
>>>>>> to make input connection to the outside world.  (With input R's ranging from
>>>>>> 1 k to 1 Meg ohm.)  I figure the opamp has some input protection and adding more
>>>>>> series R is only going to make it better.  Is that kosher?
>>>>>> (It's never caused me any problems yet.)
>>>>>>
>>>>>> George H.
>>>>>>
>>>>>>>
>>>>> [snip]
>>>>>
>>>>> Diodes from summing junction to ground will make it very robust.
>>>>
>>>> Anti-parallel.  Is that called back-to-back or belly-to-belly ?:-}
>>>>
>>> Yup.  Back-to-back is inverse series, as in "back-to-back zeners".
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>
>> So belly-to-belly anti-parallel ?:-}
>> 		
>>                                         ...Jim Thompson
>>
>This is a family show. (For values of "family" corresponding to dates 
>before 1965.)
>
>Cheers
>
>Phil Hobbs

Sno-o-o-ort >:-}

Yep.  I'm of the Ozzie & Harriet era.
		
                                        ...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.

[toc] | [prev] | [next] | [standalone]

#446925

On Wednesday, February 8, 2017 at 4:21:17 PM UTC-5, Jim Thompson wrote:
> On Wed, 8 Feb 2017 16:15:10 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
> 
> >On 02/08/2017 04:12 PM, Jim Thompson wrote:
> >> On Wed, 8 Feb 2017 16:09:14 -0500, Phil Hobbs
> >> <pcdhSpamMeSenseless@electrooptical.net> wrote:
> >>
> >>> On 02/08/2017 02:34 PM, Jim Thompson wrote:
> >>>> On Wed, 08 Feb 2017 12:20:33 -0700, Jim Thompson
> >>>> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
> >>>>
> >>>>> On Wed, 8 Feb 2017 10:58:57 -0800 (PST), George Herold
> >>>>> <gherold@teachspin.com> wrote:
> >>>>>
> >>>>> [snip
> >>>>>
> >>>>>>
> >>>>>> Say, Here's a somewhat related question.  I'll often use an inverting amp
> >>>>>> to make input connection to the outside world.  (With input R's ranging from
> >>>>>> 1 k to 1 Meg ohm.)  I figure the opamp has some input protection and adding more
> >>>>>> series R is only going to make it better.  Is that kosher?
> >>>>>> (It's never caused me any problems yet.)
> >>>>>>
> >>>>>> George H.
> >>>>>>
> >>>>>>>
> >>>>> [snip]
> >>>>>
> >>>>> Diodes from summing junction to ground will make it very robust.
> >>>>
> >>>> Anti-parallel.  Is that called back-to-back or belly-to-belly ?:-}
> >>>>
> >>> Yup.  Back-to-back is inverse series, as in "back-to-back zeners".
> >>>
> >>> Cheers
> >>>
> >>> Phil Hobbs
> >>
> >> So belly-to-belly anti-parallel ?:-}
> >> 		
> >>                                         ...Jim Thompson
> >>
> >This is a family show. (For values of "family" corresponding to dates 
> >before 1965.)
> >
> >Cheers
> >
> >Phil Hobbs
> 
> Sno-o-o-ort >:-}
> 
> Yep.  I'm of the Ozzie & Harriet era.
> 		
>                                         ...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.

Grin, I'll never think of my belly to belly,
anti parallel diodes the same way again. 
I worry about people plugging things in without the 
power on... but the diodes take care of that too!   

George H. 

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#446858

On 02/08/2017 01:58 PM, George Herold wrote:
> On Wednesday, February 8, 2017 at 11:44:23 AM UTC-5, Phil Hobbs wrote:
>> On 02/07/2017 08:47 PM, gghero27@gmail.com wrote:
>>> On Tuesday, February 7, 2017 at 4:40:24 PM UTC-5, Phil Hobbs wrote:
>>>> On 02/07/2017 03:56 PM, George Herold wrote:
>>>>> OK first a failure at Digikey.  I went searching for difference amps,
>>>>> but they are listed in many different places.  (So it's hard to look at
>>>>> them all at once.  (See table 5.7 pg 353 in AoE3)) Most are listed as
>>>>> Differential amps w/o differential outputs.  But the LT1191 is
>>>>> under programmable gain, and INA134 is under linear-amps-audio.
>>>>> (A section I'm going to have to troll a bit more... lotsa potential
>>>>> power op-amps, that I don't know about.)
>>>>>
>>>>> Anyway, I need a few difference amps.  The ina132 is a reasonable example,
>>>>> http://www.ti.com/lit/ds/symlink/ina132.pdf
>>>>> An opamp with laser trimmed resistors already in place.
>>>>>
>>>>> I've been using an instrument amp, but it's overkill.
>>>>> I've never used a difference amp.
>>>>> First question, do you expect these to go away in the future?
>>>>> (say 10 years)
>>>>> Hmm that might be my only question.  Would you use these instead
>>>>> of an opamp and 0.1% R's?
>>>>
>>>> I've used them in various test jigs and small instruments (usually the
>>>> PMI/AD AMP03 because I had a bunch of them).  They're very convenient
>>>> and the resistors track well, which is one advantage, but I'm usually
>>>> using them for strange stuff such as very accurate x1/x2 amps.
>>>>
>>>> One problem is that you have to drive all three inputs from super low-Z
>>>> sources or you'll ruin the CMR.
>>> Yeah, this is just inside a slow analog control loop, so opamps or such
>>> driving all the R's.  I don't care too much about CMR... (I think..
>>> noise and interference can tricky,)
>>> I'm adding and subtracting analog signals, I was thinking
>>> how much easier it would be with an Int amp, rather than
>>> two opamps to sum and then invert.  And then why not
>>> a difference amp.  (which I only learned about from AoE3.)
>>
>> Seems like an expensive way to save four ordinary resistors if you don't
>> care about CMR.  The AMP03's DC CMR is 100 dB typical, which is pretty
>> good for a part that old.
>
> Hmm maybe.  I was replacing an Int amp, so it's cheaper than that.
> I do care about the gain accuracy...
> I'm taking the difference between a set point and temperature, to make
> an error signal.  (As well as other even less critical stuff.)
>
> OK, I'll stick with the Int amp, that is in stock and make the other
> diff amp from an opamp and R's.
>
> Say, Here's a somewhat related question.  I'll often use an inverting amp
> to make input connection to the outside world.  (With input R's ranging from
> 1 k to 1 Meg ohm.)  I figure the opamp has some input protection and adding more
> series R is only going to make it better.  Is that kosher?
> (It's never caused me any problems yet.)
>

Not only kosher, it's an excellent idea, as long as (a) it doesn't trash 
the noise performance, and (b) you label the inputs with Rin as on an 
oscilloscope.

The resistor provides current limiting, and since the summing junction 
stays more or less still, you can add external protection networks easily.

Cheers

Phil Hobbs


-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

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#446722

On Tuesday, February 7, 2017 at 4:40:24 PM UTC-5, Phil Hobbs wrote:
> On 02/07/2017 03:56 PM, George Herold wrote:
> > OK first a failure at Digikey.  I went searching for difference amps,
> > but they are listed in many different places.  (So it's hard to look at
> > them all at once.  (See table 5.7 pg 353 in AoE3)) Most are listed as
> > Differential amps w/o differential outputs.  But the LT1191 is
> > under programmable gain, and INA134 is under linear-amps-audio.
> > (A section I'm going to have to troll a bit more... lotsa potential
> > power op-amps, that I don't know about.)
> >
> > Anyway, I need a few difference amps.  The ina132 is a reasonable example,
> > http://www.ti.com/lit/ds/symlink/ina132.pdf
> > An opamp with laser trimmed resistors already in place.
> >
> > I've been using an instrument amp, but it's overkill.
> > I've never used a difference amp.
> > First question, do you expect these to go away in the future?
> > (say 10 years)
> > Hmm that might be my only question.  Would you use these instead
> > of an opamp and 0.1% R's?
> 
> I've used them in various test jigs and small instruments (usually the 
> PMI/AD AMP03 because I had a bunch of them).  They're very convenient 
> and the resistors track well, which is one advantage, but I'm usually 
> using them for strange stuff such as very accurate x1/x2 amps.
> 
> One problem is that you have to drive all three inputs from super low-Z 
> sources or you'll ruin the CMR.
Yeah, this is just inside a slow analog control loop, so opamps or such
driving all the R's.  I don't care too much about CMR... (I think..
noise and interference can tricky,)
I'm adding and subtracting analog signals, I was thinking 
how much easier it would be with an Int amp, rather than
two opamps to sum and then invert.  And then why not 
a difference amp.  (which I only learned about from AoE3.)

Then again I've seen analog bits go away.  
(I've got a few UAF42?? (burr brown SV filter IC)
in my parts box... went away just when I built my first 
SV filter...(did I mention I often feel like I live on 
the trailing edge of technology?)  We can save a little 
by buying Int amp's in bulk... they will have a longer lifetime 
than Diff amps.

Then again again, I can see all sorts of nice ways to use, 
opamps w/R's, saves space... there're many vendors.

George H. 


> 
> Cheers
> 
> Phil Hobbs
> 
> (Just getting up from a bout of pneumonia due to a virus I brought back 
> from vacation.) :(
> 
> 
> 
> -- 
> Dr Philip C D Hobbs
> Principal Consultant
> ElectroOptical Innovations LLC
> Optics, Electro-optics, Photonics, Analog Electronics
> 
> 160 North State Road #203
> Briarcliff Manor NY 10510
> 
> hobbs at electrooptical dot net
> http://electrooptical.net

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#446708

On Tuesday, February 7, 2017 at 3:56:21 PM UTC-5, George Herold wrote:
> OK first a failure at Digikey.  I went searching for difference amps, 
> but they are listed in many different places.  (So it's hard to look at 
> them all at once.  (See table 5.7 pg 353 in AoE3)) Most are listed as 
> Differential amps w/o differential outputs.  But the LT1191 is 
> under programmable gain, and INA134 is under linear-amps-audio.  
> (A section I'm going to have to troll a bit more... lotsa potential 
> power op-amps, that I don't know about.)  
> 
> Anyway, I need a few difference amps.  The ina132 is a reasonable example,
> http://www.ti.com/lit/ds/symlink/ina132.pdf  
> An opamp with laser trimmed resistors already in place.  
> 
> I've been using an instrument amp, but it's overkill.  
> I've never used a difference amp.  
> First question, do you expect these to go away in the future?  
> (say 10 years)  
> Hmm that might be my only question.  Would you use these instead 
> of an opamp and 0.1% R's?   
> 
> Thanks 
> 
> George H.

I've used the INA128 a few times, no complaints about it.

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#446723

On Tuesday, February 7, 2017 at 7:20:55 PM UTC-5, sdy wrote:
> On Tuesday, February 7, 2017 at 3:56:21 PM UTC-5, George Herold wrote:
> > OK first a failure at Digikey.  I went searching for difference amps, 
> > but they are listed in many different places.  (So it's hard to look at 
> > them all at once.  (See table 5.7 pg 353 in AoE3)) Most are listed as 
> > Differential amps w/o differential outputs.  But the LT1191 is 
> > under programmable gain, and INA134 is under linear-amps-audio.  
> > (A section I'm going to have to troll a bit more... lotsa potential 
> > power op-amps, that I don't know about.)  
> > 
> > Anyway, I need a few difference amps.  The ina132 is a reasonable example,
> > http://www.ti.com/lit/ds/symlink/ina132.pdf  
> > An opamp with laser trimmed resistors already in place.  
> > 
> > I've been using an instrument amp, but it's overkill.  
> > I've never used a difference amp.  
> > First question, do you expect these to go away in the future?  
> > (say 10 years)  
> > Hmm that might be my only question.  Would you use these instead 
> > of an opamp and 0.1% R's?   
> > 
> > Thanks 
> > 
> > George H.
> 
> I've used the INA128 a few times, no complaints about it.

Thanks,  I'm gonna order some.  (someone has to use these parts.)

George H. 

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#446852

On Tue, 7 Feb 2017 17:50:47 -0800 (PST), gghero27@gmail.com wrote:

>On Tuesday, February 7, 2017 at 7:20:55 PM UTC-5, sdy wrote:
>> On Tuesday, February 7, 2017 at 3:56:21 PM UTC-5, George Herold wrote:
>> > OK first a failure at Digikey.  I went searching for difference amps, 
>> > but they are listed in many different places.  (So it's hard to look at 
>> > them all at once.  (See table 5.7 pg 353 in AoE3)) Most are listed as 
>> > Differential amps w/o differential outputs.  But the LT1191 is 
>> > under programmable gain, and INA134 is under linear-amps-audio.  
>> > (A section I'm going to have to troll a bit more... lotsa potential 
>> > power op-amps, that I don't know about.)  
>> > 
>> > Anyway, I need a few difference amps.  The ina132 is a reasonable example,
>> > http://www.ti.com/lit/ds/symlink/ina132.pdf  
>> > An opamp with laser trimmed resistors already in place.  
>> > 
>> > I've been using an instrument amp, but it's overkill.  
>> > I've never used a difference amp.  
>> > First question, do you expect these to go away in the future?  
>> > (say 10 years)  
>> > Hmm that might be my only question.  Would you use these instead 
>> > of an opamp and 0.1% R's?   
>> > 
>> > Thanks 
>> > 
>> > George H.
>> 
>> I've used the INA128 a few times, no complaints about it.
>
>Thanks,  I'm gonna order some.  (someone has to use these parts.)
>
>George H. 

This is what we have in stock:

ICS DIFFAMP  18V SO8 1X       INA117 200KHz
ICS DIFFAMP  40V SO8 1X       INA154 G=1
ICS DIFFAMP  44V DIP8 1X      SSM2017 OBS
ICS DIFFAMP  36V DIP8 1X      INA105KP G=1
ICS DIFFAMP  36V SO8 1X       INA105KU G=1
ICS DIFFAMP  36V SO8 1X       INA157 G=0.5/2
ICS DIFFAMP  34V MSOP10 1X    AD8253 PGA
ICS DIFFAMP  50V SO16W 1X     INA103KU INST
ICS DIFFAMP  36V SO16W 1X     INA111 FET VG
ICS DIFFAMP  36V DIP8 1X      INA114 VG OVP
ICS DIFFAMP  36V SO16W 1X     INA115 OVP VG
ICS DIFFAMP  36V SO8 1X       INA129 VG
ICS DIFFAMP  36V SO8 1X       INA141 OVP
ICS DIFFAMP  36V SO8 1X       AD8221 800KHZ 400PA 8NV
ICS DIFFAMP  3V QFN16 1X      ADA4950-1 ADC DRVR
ICS DIFFAMP  5V QFN16 1X      ADA4960 ADC DRVR
ICS DIFFAMP  26V SO8 1X       AD8130 270MHZ
ICS DIFFAMP  15V MSOP8P X1    THS4505 260M
ICS DIFFAMP  5V QFN16 1X      LT6402-12 ADC DRVR


We don't use the DIP parts much any more.






-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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#446716

On Tue, 7 Feb 2017 12:56:11 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

>OK first a failure at Digikey.  I went searching for difference amps, 
>but they are listed in many different places.  (So it's hard to look at 
>them all at once.  (See table 5.7 pg 353 in AoE3)) Most are listed as 
>Differential amps w/o differential outputs.  But the LT1191 is 
>under programmable gain, and INA134 is under linear-amps-audio.  
>(A section I'm going to have to troll a bit more... lotsa potential 
>power op-amps, that I don't know about.)  
>
>Anyway, I need a few difference amps.  The ina132 is a reasonable example,
>http://www.ti.com/lit/ds/symlink/ina132.pdf  
>An opamp with laser trimmed resistors already in place.  
>
>I've been using an instrument amp, but it's overkill.  
>I've never used a difference amp.  
>First question, do you expect these to go away in the future?  
>(say 10 years)  

They are pretty common and there are lots of equivalents. I think they
are here to stay.

>Hmm that might be my only question.  Would you use these instead 
>of an opamp and 0.1% R's? 

A difference amp, with tracking laser-trimmed resistors inside, is
fairly cheap.
  
One cool part is AD8130, 270 MHz, interesting architecture.


-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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#446720

John Larkin wrote...
>
>> Hmm that might be my only question.  Would you
>> use these instead of an opamp and 0.1% R's? 
>
> A difference amp, with tracking laser-trimmed
> resistors inside, is fairly cheap.

 Right.  These parts aren't going to disappear.
 Most of the popular versions shown in our 1989
 2nd edition are still going strong, and will
 for decades to come.
  
> One cool part is AD8130, 270 MHz, interesting
> architecture.

 The high-frequency gain and good CMRR is nice, but
 since it uses the cancellation of two differential
 BJT g_m stages as its input, it isn't a precision
 part, like a fine op-amp + 0.01% matched resistors.


-- 
 Thanks,
    - Win

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#446818

Winfield Hill wrote:
>
>  Right.  These parts aren't going to disappear.
>  Most of the popular versions shown in our 1989
>  2nd edition are still going strong, and will
>  for decades to come.

Until it's the last low-volume product that won't be transferred onto the
next wafer size or a different fab.

robert

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