Reply by krw...@att.bizzzzzzzzzzzz May 24, 20122012-05-24
On Thu, 24 May 2012 09:52:03 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On May 24, 11:47&#2013266080;am, Tauno Voipio <tauno.voi...@notused.fi.invalid> >wrote: >> On 23.5.12 4:52 , George Herold wrote: >> >> > &#2013266080; I reinvented the two opamp differential amp yesterday. >> > And then found it in AofE* (2nd Ed. figure 7.36). &#2013266080;Though I drew it >> > differently. >> >> > &#2013266080; &#2013266080;+-R2--+--R1--+ >> > &#2013266080; &#2013266080;| &#2013266080; &#2013266080; | |\U1 | &#2013266080; &#2013266080;+--R2--+ >> > &#2013266080; gnd &#2013266080; &#2013266080;+-|-\ &#2013266080;| &#2013266080; &#2013266080;| |\U2 | >> > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;|>-+-R1-+-|-\ &#2013266080;| >> > &#2013266080; V(-)-----|+/ &#2013266080; &#2013266080; &#2013266080; &#2013266080; |>-+--out >> > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;|/ &#2013266080; V(+)---|+/ >> > &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;|/ >> >> > Thanks, >> > George H. >> >> Go ahead and add the third opamp to reinvent the >> classical instrumentation amp. > >Grin, Yeah, but then I'd have to stick another DIP on my copper >clad. I'm mostly a one chip wonder. Two IC's and I start to become >confused :^)
Use a quad.
Reply by George Herold May 24, 20122012-05-24
On May 24, 11:47=A0am, Tauno Voipio <tauno.voi...@notused.fi.invalid>
wrote:
> On 23.5.12 4:52 , George Herold wrote: > > > =A0 I reinvented the two opamp differential amp yesterday. > > And then found it in AofE* (2nd Ed. figure 7.36). =A0Though I drew it > > differently. > > > =A0 =A0+-R2--+--R1--+ > > =A0 =A0| =A0 =A0 | |\U1 | =A0 =A0+--R2--+ > > =A0 gnd =A0 =A0+-|-\ =A0| =A0 =A0| |\U2 | > > =A0 =A0 =A0 =A0 =A0 =A0|>-+-R1-+-|-\ =A0| > > =A0 V(-)-----|+/ =A0 =A0 =A0 =A0 |>-+--out > > =A0 =A0 =A0 =A0 =A0 =A0|/ =A0 V(+)---|+/ > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|/ > > > Thanks, > > George H. > > Go ahead and add the third opamp to reinvent the > classical instrumentation amp.
Grin, Yeah, but then I'd have to stick another DIP on my copper clad. I'm mostly a one chip wonder. Two IC's and I start to become confused :^) George H.
> > -- > > Tauno Voipio
Reply by George Herold May 24, 20122012-05-24
On May 24, 10:18=A0am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Thu, 24 May 2012 06:06:52 -0700 (PDT), George Herold > > > > > > <gher...@teachspin.com> wrote: > >On May 24, 2:37=A0am, Fred Bartoli <" "> wrote: > >> George Herold a =E9crit : > > >> > On May 23, 9:52 am, George Herold <gher...@teachspin.com> wrote: > >> >> =A0I reinvented the two opamp differential amp yesterday. > >> >> And then found it in AofE* (2nd Ed. figure 7.36). =A0Though I drew =
it
> >> >> differently. > > >> >> =A0 +-R2--+--R1--+ > >> >> =A0 | =A0 =A0 | |\U1 | =A0 =A0+--R2--+ > >> >> =A0gnd =A0 =A0+-|-\ =A0| =A0 =A0| |\U2 | > >> >> =A0 =A0 =A0 =A0 =A0 | =A0>-+-R1-+-|-\ =A0| > >> >> =A0V(-)-----|+/ =A0 =A0 =A0 =A0 | =A0>-+--out > >> >> =A0 =A0 =A0 =A0 =A0 |/ =A0 V(+)---|+/ > >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |/ > > >> >> It=92s a natural addition to the single opamp difference amp. > >> >> (boost up V(-) rather than throw away V(+). (G =3D 1 + R2/R1) > > >> >> The output of the first opamp U1 bothers me a bit. =A0As it has to > >> >> handle the current from U2=92s gain. =A0I=92d like to run this up a=
t high
> >> >> frequency, and I=92m worried about the output impedance of U1 screw=
ing
> >> >> up the CMRR. =A0My current thought was to keep the gain low, and us=
e
> >> >> R2=3D1k and R1=3D 10k. That should help minimize output impedance e=
ffects.
> > >> >> Anyone used this configuration? > >> >> Or other thoughts/ comments? > > >> >> Thanks, > >> >> George H. > > >> >> *I think I really did reinvent it... but then seeing it in AofE I > >> >> wonder if the back of my brain is just remembering it. > > >> > This circuit stinks, for anything that wants to be fast. =A0The V(-) > >> > input has to go through two opamps, with the output delayed about > >> > 100ns from the V(+). =A0(opamps was opa2134) > > >> > George H. > > >> How much fast is fast? > > >Grin... that's always a good question, short answer is better than I > >have now. =A0I'd like to do ~100ns pulses. =A0But making things even > >faster might be interesting. > > >> See AD8129/8130 for a single opamp solution... > > >Thanks I'll give those a look see. =A0I was looking at the AD8429 > >instument amp yesterday. =A012 MHz at unity gain, but all sorts of > >ringing on the step response. > > >George H. > > AD8130 is a great part, 270 MHz and very clean. Just be careful not to > exceed the maximum 2.5 volts diff input. It *will* clip just a bit > past there. > > -- > > John Larkin =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Highland Technology Incwww=
.highlandtechnology.com=A0 jlarkin at highlandtechnology dot com
> > Precision electronic instrumentation > Picosecond-resolution Digital Delay and Pulse generators > Custom timing and laser controllers > Photonics and fiberoptic TTL data links > VME =A0analog, thermocouple, LVDT, synchro, tachometer > Multichannel arbitrary waveform generators- Hide quoted text - > > - Show quoted text -
Roger, no more than 2.5 Volts. Differential receiver amps are on order. Half the problem is knowing what to search for. Hey, I got the active quench to work! +Vbias | R=3D1k | +---+----+ | | | 10k L C ~10pF | E | +--R---+ R=92s =3D 10k |/ D | | |\ | +-| | +-R--+-|-\ | | |\> | | >-+---> to comparator | | +------R--+-|+/ | GND | |/ opa134 | R +-<quench | pulse from GND comparator There are some =91tweaker=92 C=92s (5.6pF) on the feedback R and R to groun= d of non-inverting input. These gave the diff amp a nice pulse response. Here=92s a scope shot. http://bayimg.com/iAOjoaAdM Chan. 1 is diff amp output chan. 2 is the =91quench=92 pulse chan 3 is the voltage change at the top of the LED. (AC coupled) I got to use the four channel =91scope. Things could certainly be faster. But it works! George H.
Reply by Tauno Voipio May 24, 20122012-05-24
On 23.5.12 4:52 , George Herold wrote:
> I reinvented the two opamp differential amp yesterday. > And then found it in AofE* (2nd Ed. figure 7.36). Though I drew it > differently. > > +-R2--+--R1--+ > | | |\U1 | +--R2--+ > gnd +-|-\ | | |\U2 | > |>-+-R1-+-|-\ | > V(-)-----|+/ |>-+--out > |/ V(+)---|+/ > |/ > > Thanks, > George H.
Go ahead and add the third opamp to reinvent the classical instrumentation amp. -- Tauno Voipio
Reply by John Larkin May 24, 20122012-05-24
On Thu, 24 May 2012 06:06:52 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On May 24, 2:37&#2013266080;am, Fred Bartoli <" "> wrote: >> George Herold a &#2013265929;crit : >> >> >> >> >> >> > On May 23, 9:52 am, George Herold <gher...@teachspin.com> wrote: >> >> &#2013266080;I reinvented the two opamp differential amp yesterday. >> >> And then found it in AofE* (2nd Ed. figure 7.36). &#2013266080;Though I drew it >> >> differently. >> >> >> &#2013266080; +-R2--+--R1--+ >> >> &#2013266080; | &#2013266080; &#2013266080; | |\U1 | &#2013266080; &#2013266080;+--R2--+ >> >> &#2013266080;gnd &#2013266080; &#2013266080;+-|-\ &#2013266080;| &#2013266080; &#2013266080;| |\U2 | >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080;>-+-R1-+-|-\ &#2013266080;| >> >> &#2013266080;V(-)-----|+/ &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080;>-+--out >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; |/ &#2013266080; V(+)---|+/ >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; |/ >> >> >> It&#2013266066;s a natural addition to the single opamp difference amp. >> >> (boost up V(-) rather than throw away V(+). (G = 1 + R2/R1) >> >> >> The output of the first opamp U1 bothers me a bit. &#2013266080;As it has to >> >> handle the current from U2&#2013266066;s gain. &#2013266080;I&#2013266066;d like to run this up at high >> >> frequency, and I&#2013266066;m worried about the output impedance of U1 screwing >> >> up the CMRR. &#2013266080;My current thought was to keep the gain low, and use >> >> R2=1k and R1= 10k. That should help minimize output impedance effects. >> >> >> Anyone used this configuration? >> >> Or other thoughts/ comments? >> >> >> Thanks, >> >> George H. >> >> >> *I think I really did reinvent it... but then seeing it in AofE I >> >> wonder if the back of my brain is just remembering it. >> >> > This circuit stinks, for anything that wants to be fast. &#2013266080;The V(-) >> > input has to go through two opamps, with the output delayed about >> > 100ns from the V(+). &#2013266080;(opamps was opa2134) >> >> > George H. >> >> How much fast is fast? > >Grin... that's always a good question, short answer is better than I >have now. I'd like to do ~100ns pulses. But making things even >faster might be interesting. >> >> See AD8129/8130 for a single opamp solution... > >Thanks I'll give those a look see. I was looking at the AD8429 >instument amp yesterday. 12 MHz at unity gain, but all sorts of >ringing on the step response. > >George H. >>
AD8130 is a great part, 270 MHz and very clean. Just be careful not to exceed the maximum 2.5 volts diff input. It *will* clip just a bit past there. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by George Herold May 24, 20122012-05-24
On May 24, 2:37=A0am, Fred Bartoli <" "> wrote:
> George Herold a =E9crit : > > > > > > > On May 23, 9:52 am, George Herold <gher...@teachspin.com> wrote: > >> =A0I reinvented the two opamp differential amp yesterday. > >> And then found it in AofE* (2nd Ed. figure 7.36). =A0Though I drew it > >> differently. > > >> =A0 +-R2--+--R1--+ > >> =A0 | =A0 =A0 | |\U1 | =A0 =A0+--R2--+ > >> =A0gnd =A0 =A0+-|-\ =A0| =A0 =A0| |\U2 | > >> =A0 =A0 =A0 =A0 =A0 | =A0>-+-R1-+-|-\ =A0| > >> =A0V(-)-----|+/ =A0 =A0 =A0 =A0 | =A0>-+--out > >> =A0 =A0 =A0 =A0 =A0 |/ =A0 V(+)---|+/ > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |/ > > >> It=92s a natural addition to the single opamp difference amp. > >> (boost up V(-) rather than throw away V(+). (G =3D 1 + R2/R1) > > >> The output of the first opamp U1 bothers me a bit. =A0As it has to > >> handle the current from U2=92s gain. =A0I=92d like to run this up at h=
igh
> >> frequency, and I=92m worried about the output impedance of U1 screwing > >> up the CMRR. =A0My current thought was to keep the gain low, and use > >> R2=3D1k and R1=3D 10k. That should help minimize output impedance effe=
cts.
> > >> Anyone used this configuration? > >> Or other thoughts/ comments? > > >> Thanks, > >> George H. > > >> *I think I really did reinvent it... but then seeing it in AofE I > >> wonder if the back of my brain is just remembering it. > > > This circuit stinks, for anything that wants to be fast. =A0The V(-) > > input has to go through two opamps, with the output delayed about > > 100ns from the V(+). =A0(opamps was opa2134) > > > George H. > > How much fast is fast?
Grin... that's always a good question, short answer is better than I have now. I'd like to do ~100ns pulses. But making things even faster might be interesting.
> > See AD8129/8130 for a single opamp solution...
Thanks I'll give those a look see. I was looking at the AD8429 instument amp yesterday. 12 MHz at unity gain, but all sorts of ringing on the step response. George H.
> > -- > Thanks, > Fred.- Hide quoted text - > > - Show quoted text -
Reply by Fred Bartoli May 24, 20122012-05-24
George Herold a &#2013265929;crit :
> On May 23, 9:52 am, George Herold <gher...@teachspin.com> wrote: >> I reinvented the two opamp differential amp yesterday. >> And then found it in AofE* (2nd Ed. figure 7.36). Though I drew it >> differently. >> >> +-R2--+--R1--+ >> | | |\U1 | +--R2--+ >> gnd +-|-\ | | |\U2 | >> | >-+-R1-+-|-\ | >> V(-)-----|+/ | >-+--out >> |/ V(+)---|+/ >> |/ >> >> It&#2013266066;s a natural addition to the single opamp difference amp. >> (boost up V(-) rather than throw away V(+). (G = 1 + R2/R1) >> >> The output of the first opamp U1 bothers me a bit. As it has to >> handle the current from U2&#2013266066;s gain. I&#2013266066;d like to run this up at high >> frequency, and I&#2013266066;m worried about the output impedance of U1 screwing >> up the CMRR. My current thought was to keep the gain low, and use >> R2=1k and R1= 10k. That should help minimize output impedance effects. >> >> Anyone used this configuration? >> Or other thoughts/ comments? >> >> Thanks, >> George H. >> >> *I think I really did reinvent it... but then seeing it in AofE I >> wonder if the back of my brain is just remembering it. > > This circuit stinks, for anything that wants to be fast. The V(-) > input has to go through two opamps, with the output delayed about > 100ns from the V(+). (opamps was opa2134) > > George H.
How much fast is fast? See AD8129/8130 for a single opamp solution... -- Thanks, Fred.
Reply by George Herold May 23, 20122012-05-23
On May 23, 9:52=A0am, George Herold <gher...@teachspin.com> wrote:
> =A0I reinvented the two opamp differential amp yesterday. > And then found it in AofE* (2nd Ed. figure 7.36). =A0Though I drew it > differently. > > =A0 +-R2--+--R1--+ > =A0 | =A0 =A0 | |\U1 | =A0 =A0+--R2--+ > =A0gnd =A0 =A0+-|-\ =A0| =A0 =A0| |\U2 | > =A0 =A0 =A0 =A0 =A0 | =A0>-+-R1-+-|-\ =A0| > =A0V(-)-----|+/ =A0 =A0 =A0 =A0 | =A0>-+--out > =A0 =A0 =A0 =A0 =A0 |/ =A0 V(+)---|+/ > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |/ > > It=92s a natural addition to the single opamp difference amp. > (boost up V(-) rather than throw away V(+). (G =3D 1 + R2/R1) > > The output of the first opamp U1 bothers me a bit. =A0As it has to > handle the current from U2=92s gain. =A0I=92d like to run this up at high > frequency, and I=92m worried about the output impedance of U1 screwing > up the CMRR. =A0My current thought was to keep the gain low, and use > R2=3D1k and R1=3D 10k. That should help minimize output impedance effects=
.
> > Anyone used this configuration? > Or other thoughts/ comments? > > Thanks, > George H. > > *I think I really did reinvent it... but then seeing it in AofE I > wonder if the back of my brain is just remembering it.
This circuit stinks, for anything that wants to be fast. The V(-) input has to go through two opamps, with the output delayed about 100ns from the V(+). (opamps was opa2134) George H.
Reply by George Herold May 23, 20122012-05-23
 I reinvented the two opamp differential amp yesterday.
And then found it in AofE* (2nd Ed. figure 7.36).  Though I drew it
differently.

  +-R2--+--R1--+
  |     | |\U1 |    +--R2--+
 gnd    +-|-\  |    | |\U2 |
          |  >-+-R1-+-|-\  |
 V(-)-----|+/         |  >-+--out
          |/   V(+)---|+/
                      |/

It=92s a natural addition to the single opamp difference amp.
(boost up V(-) rather than throw away V(+). (G =3D 1 + R2/R1)

The output of the first opamp U1 bothers me a bit.  As it has to
handle the current from U2=92s gain.  I=92d like to run this up at high
frequency, and I=92m worried about the output impedance of U1 screwing
up the CMRR.  My current thought was to keep the gain low, and use
R2=3D1k and R1=3D 10k. That should help minimize output impedance effects.

Anyone used this configuration?
Or other thoughts/ comments?

Thanks,
George H.


*I think I really did reinvent it... but then seeing it in AofE I
wonder if the back of my brain is just remembering it.