Technical question about good low power rail to rail opamp
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From: Hammy on 12 Apr 2010 14:26 On Mon, 12 Apr 2010 13:41:20 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >>The THS422X may be overkill but off the top of my head.... >> >>http://focus.ti.com/lit/ds/symlink/ths4222.pdf > >Yes that is nice, but also consumes quite a bit of current... that I do not have. > >Thank you. Yea the THS422X IS a bit of a brute;-) I went through my opamp data sheets and found this.4.3mA/ch ..Availiable in a quad.Low power shutdown mode. http://focus.ti.com/docs/prod/folders/print/opa727.html The TLV2372 Is a decent low power opamp but its slow 2.4 V/us
From: Jan Panteltje on 12 Apr 2010 14:55 n a sunny day (Mon, 12 Apr 2010 12:56:52 -0500) it happened "Tim Williams" <tmoranwms(a)charter.net> wrote in <hpvmt7$8fg$1(a)news.eternal-september.org>: >TLV2372? That looks good. It is just fast enough and has a 4 in a package version And I can but it here and it is in stock. one for ch 1, one for ch 2, one for trigger, and one for DC shift perhaps. >Kind of an LM358 including the top rail, with lower current... response >about the same. Bandwidth isn't "low" but maybe it's not 10V/us. > >The FET follower will work if you add a trimpot and another JFET to >compensate it. If you don't want a trimpot and the extra 4 transistors, you >might as well use an op-amp. Fewer pins for sure. > >Tim Yes, need a lot more transistors then, more space, more expensive, I like this opamp, it does not have all those weird curves some of the others have. I came up with OP482 myself this afternoon, but that is more expensive. The TLV2374 quad goes for about 1 Euro here.
From: Jan Panteltje on 12 Apr 2010 14:57 On a sunny day (Tue, 13 Apr 2010 04:21:36 +1000) it happened David Eather <eather(a)tpg.com.au> wrote in <lYCdnfzwxbsp-V7WnZ2dnUVZ_gydnZ2d(a)supernews.com>: >On 12/04/2010 9:33 PM, Jan Panteltje wrote: >> Technical question about good low power rail to rail opamp. >> I published 'scope_pic' >> http://panteltje.com/panteltje/pic/scope_pic/ >> and am getting questions as 'to where to connect the input etc..'. >> >> The question is how to make a 1 MOhm, few pF, input with a bandwidth of about 1MHz, >> with as few components as possible, that also creates a +2V DC offset >> (to get the ADC midrange and allow negative signals), >> >> Now My first idea was to make a JFET input, tried something in spice like this: >> ftp://panteltje.com/pub/fet.gif >> >> There is a lot of spread in individual jfets, and the only negative voltage >> available is a tap of the -8 V from a MAX232. >> >> So that leaves opamps, and the ones I found (5V rail to rail) >> have either low bandwidth, bad slew rates, >> incredible distortion, or all of those at the same time. >> >> So I am looking for a decent quad 5V to 12 supply opamp with low current draw, >> only needs to drive a PIC input, say 10k in 25 pF, with low distortion, high >> gain, slew rate> 10V us, voltage swing to very near the positive supply, >> input impedance 00, input cap< 10 pF. >> >> I looked at LMC6036, some others, but no good. >> Any ideas? >> So it is for the scope input amp. > >Why are you stuck with only a +5v rail. Can't you use any voltage rails >you like for the op amp and shift the output and alter the gain >independently? (and if you need to add some diodes to keep the output >clamped between 0 - 5 volts) I am using -8V from a MAX 232 output as negaive rail :-) and possibly the +8 from an other output as positive rail. That solution is hereby copyrighed. hehe
From: Jan Panteltje on 12 Apr 2010 15:01 On a sunny day (Mon, 12 Apr 2010 14:26:02 -0400) it happened Hammy <spam(a)spam.com> wrote in <ifo6s5t2rt8pgooodajrie6k4urh1mlv13(a)4ax.com>: >On Mon, 12 Apr 2010 13:41:20 GMT, Jan Panteltje ><pNaonStpealmtje(a)yahoo.com> wrote: > > >>>The THS422X may be overkill but off the top of my head.... >>> >>>http://focus.ti.com/lit/ds/symlink/ths4222.pdf >> >>Yes that is nice, but also consumes quite a bit of current... that I do not have. >> >>Thank you. > >Yea the THS422X IS a bit of a brute;-) > >I went through my opamp data sheets and found this.4.3mA/ch >.Availiable in a quad.Low power shutdown mode. > >http://focus.ti.com/docs/prod/folders/print/opa727.html > >The TLV2372 Is a decent low power opamp but its slow 2.4 V/us OK, but those are +/-5V, and I want to run from +5 -8.
From: David Eather on 12 Apr 2010 15:07
On 13/04/2010 4:57 AM, Jan Panteltje wrote: > On a sunny day (Tue, 13 Apr 2010 04:21:36 +1000) it happened David Eather > <eather(a)tpg.com.au> wrote in<lYCdnfzwxbsp-V7WnZ2dnUVZ_gydnZ2d(a)supernews.com>: > >> On 12/04/2010 9:33 PM, Jan Panteltje wrote: >>> Technical question about good low power rail to rail opamp. >>> I published 'scope_pic' >>> http://panteltje.com/panteltje/pic/scope_pic/ >>> and am getting questions as 'to where to connect the input etc..'. >>> >>> The question is how to make a 1 MOhm, few pF, input with a bandwidth of about 1MHz, >>> with as few components as possible, that also creates a +2V DC offset >>> (to get the ADC midrange and allow negative signals), >>> >>> Now My first idea was to make a JFET input, tried something in spice like this: >>> ftp://panteltje.com/pub/fet.gif >>> >>> There is a lot of spread in individual jfets, and the only negative voltage >>> available is a tap of the -8 V from a MAX232. >>> >>> So that leaves opamps, and the ones I found (5V rail to rail) >>> have either low bandwidth, bad slew rates, >>> incredible distortion, or all of those at the same time. >>> >>> So I am looking for a decent quad 5V to 12 supply opamp with low current draw, >>> only needs to drive a PIC input, say 10k in 25 pF, with low distortion, high >>> gain, slew rate> 10V us, voltage swing to very near the positive supply, >>> input impedance 00, input cap< 10 pF. >>> >>> I looked at LMC6036, some others, but no good. >>> Any ideas? >>> So it is for the scope input amp. >> >> Why are you stuck with only a +5v rail. Can't you use any voltage rails >> you like for the op amp and shift the output and alter the gain >> independently? (and if you need to add some diodes to keep the output >> clamped between 0 - 5 volts) > > I am using -8V from a MAX 232 output as negaive rail :-) > and possibly the +8 from an other output as positive rail. > That solution is hereby copyrighed. > hehe > Sorry - a few published PIC programmers have beaten you to that idea. |