pulse response overshoot in a follower configuration
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From: John Larkin on 9 Aug 2010 21:16 On Mon, 9 Aug 2010 15:18:24 -0700 (PDT), "miso(a)sushi.com" <miso(a)sushi.com> wrote: >On Aug 9, 2:18�pm, "jch4416" <otter30(a)n_o_s_p_a_m.bellsouth.net> >wrote: >> Hello, >> >> Is anyone familiar with any techniques for reducing overshoot in the pulse >> response of a unity gain op amp follower configuration? >> >> Thanks, >> Jim >> >> --------------------------------------- � � � � >> Posted throughhttp://www.Electronics-Related.com > >If the overshoot is due to capacitive loading, you can insert a >resistor in series with the output, but in the feedback loop. This is >in the National apps. > >If the amp itself has overshoot, I don't see any really good solution >unless it is externally compensated. I suppose you could divide the >signal by two and then set up the op amp for a gain of two. That would >increase the phase margin. Some opamps have diodes between the two inputs. Fun stuff can happen if you drive a follower faster than its native slew rate. John
From: markp on 10 Aug 2010 09:00 "jch4416" <otter30(a)n_o_s_p_a_m.bellsouth.net> wrote in message news:SoidnZIaJZsA7f3RRVn_vwA(a)giganews.com... > Hello, > > Is anyone familiar with any techniques for reducing overshoot in the pulse > response of a unity gain op amp follower configuration? > > Thanks, > Jim Here's some useful info. You might get away with just a snubber network on the output: http://www.analog.com/library/analogdialogue/archives/38-06/capacitive_loading.pdf Mark.
From: miso on 11 Aug 2010 02:07 On Aug 10, 6:00 am, "markp" <map.nos...(a)f2s.com> wrote: > "jch4416" <otter30(a)n_o_s_p_a_m.bellsouth.net> wrote in message > > news:SoidnZIaJZsA7f3RRVn_vwA(a)giganews.com... > > > Hello, > > > Is anyone familiar with any techniques for reducing overshoot in the pulse > > response of a unity gain op amp follower configuration? > > > Thanks, > > Jim > > Here's some useful info. You might get away with just a snubber network on > the output:http://www.analog.com/library/analogdialogue/archives/38-06/capacitiv... > > Mark. Good article. I'd use figure 3. I think snubbing is trickier than the paper indicates. GBW has a tempco. Output stage "native" impedance is a function of load current. I just don't see snubbing being very reliable, though I have no first hand experience at this. Figure 3 is used in lots of DUT boards.
From: George Herold on 12 Aug 2010 18:46
On Aug 11, 2:07 am, "m...(a)sushi.com" <m...(a)sushi.com> wrote: > On Aug 10, 6:00 am, "markp" <map.nos...(a)f2s.com> wrote: > > > > > > > "jch4416" <otter30(a)n_o_s_p_a_m.bellsouth.net> wrote in message > > >news:SoidnZIaJZsA7f3RRVn_vwA(a)giganews.com... > > > > Hello, > > > > Is anyone familiar with any techniques for reducing overshoot in the pulse > > > response of a unity gain op amp follower configuration? > > > > Thanks, > > > Jim > > > Here's some useful info. You might get away with just a snubber network on > > the output:http://www.analog.com/library/analogdialogue/archives/38-06/capacitiv... > > > Mark. > > Good article. I'd use figure 3. I think snubbing is trickier than the > paper indicates. GBW has a tempco. Output stage "native" impedance is > a function of load current. I just don't see snubbing being very > reliable, though I have no first hand experience at this. Figure 3 is > used in lots of DUT boards. That is nice. I've used the figure 3. circuit, but always found 'usable' values by mucking about. (While looking at the step response.) Do you know of a better reference for the derivation following figure 3? I don't quite get why I should equate the pole's and opposite zero's of the two circuit cases. C-f shorted and C-load open. Oh for any reading along at home, I found it easier to rewrite the equation for Cf in terms of two 'times'. The output time Cl*Ro = To and the feedback time Cf*Rf = Tf. The remaining two terms are then the one with the loop gain. (something near one for gains above 5 or so) and (1+Rin/Rf) a bit more than one for reasonable gains. So except for a factor near unity, Tf = To. (And I'm still going to pick the cap and muck about... I just have a better starting value. Thanks) George H. |