Technical question about good low power rail to rail opamp
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From: Joerg on 12 Apr 2010 15:30 Jan Panteltje wrote: > 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. Li'l zener diode in series? -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jan Panteltje on 12 Apr 2010 17:20 On a sunny day (Tue, 13 Apr 2010 05:07:58 +1000) it happened David Eather <eather(a)tpg.com.au> wrote in <lPednfQYS8YT8l7WnZ2dnUVZ_qSdnZ2d(a)supernews.com>: >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. Good, then we know it works :-)
From: Nico Coesel on 12 Apr 2010 17:26 Jan Panteltje <pNaonStpealmtje(a)yahoo.com> 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. I don't see low cost :-) ST has some nice rail-to-rail opamps. TS924 and TS974 come to mind. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico(a)nctdevpuntnl (punt=.) --------------------------------------------------------------
From: Jan Panteltje on 12 Apr 2010 17:42 On a sunny day (Mon, 12 Apr 2010 21:26:28 GMT) it happened nico(a)puntnl.niks (Nico Coesel) wrote in <4bc38ee2.1225974250(a)news.planet.nl>: >Jan Panteltje <pNaonStpealmtje(a)yahoo.com> 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. > >I don't see low cost :-) ST has some nice rail-to-rail opamps. TS924 >and TS974 come to mind. Nice, but a bit high current :-) Seems to be directed at the audiophile market?
From: Robert Baer on 12 Apr 2010 21:11
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. !!MAXIM parts??? They actually _exist_??? Gag me with a spoon! |