[time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors

[Azelio Boriani]

Thanks. Me too: now I got it, sort of bootstrap and now I see that R2 is
needed because the real filter is R2*C2 and the leakage is not totally
compensated if C1 has to move to a new value -> R*C1<R2*C2.

On Fri, Jan 6, 2012 at 12:00 AM, paul swed <paulswedb at gmail.com> wrote:

> Poul
> Thanks have been kind of following this thread and the diagram did not make
> a lot of sense.
> I figured I missed part of the thread. But this clears it up nicely.
> Regards
> Paul.
> WB8TSL
>
> On Thu, Jan 5, 2012 at 5:49 PM, Poul-Henning Kamp <phk at phk.freebsd.dk
> >wrote:
>
> > In message <CAL8XPmO76XuTETZC=33_v2YWuJGcw8gCvtTDHyae6E4MFb18=
> > g at mail.gmail.com>
> > , Azelio Boriani writes:
> >
> > >I have googled extensively trying to find something about the dual
> > >capacitor method of reducing the leakage current... nothing found.
> Please,
> > >can you indicate anything for me to learn more?
> >
> > It is very simple:
> >
> > R1 charges C1 to the DC potential and therefore C2 sees
> > (almost) no DC voltage, which means (almost) no leakage
> > current.  C2 is still a capacitor for any AC or dV component.
> >
> > I belive I picked this trick up from a datasheet or app-note relating
> > to precision voltage references.
> >
> > Poul-Henning
> >
> > >> [Some op-amp]  >-+-----R2-----+-->
> > >>                  |            |
> > >>                  |          ----- C2
> > >>                  |          -----
> > >>                  |    ____    |
> > >>                  +---|____|---+
> > >>                        R1     |
> > >>                               |
> > >>                             -----  C1
> > >>                             -----
> > >>                               |
> > >>                              GND
> >
> > --
> > Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> > phk at FreeBSD.ORG         | TCP/IP since RFC 956
> > FreeBSD committer       | BSD since 4.3-tahoe
> > Never attribute to malice what can adequately be explained by
> incompetence.
> >
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