[time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors
Bob Camp
lists at rtty.us
Fri Jan 6 17:54:23 UTC 2012
Hi
Oddly enough, if you use a tantalum electrolytic as C2, it's not very happy
in that circuit. Their leakage with low voltages on them can be pretty
nasty.
Bob
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Poul-Henning Kamp
Sent: Thursday, January 05, 2012 5:50 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors
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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