[sdiy] Guard Rings

Harry Bissell harrybissell at wowway.com
Fri Nov 5 14:46:37 CET 2010


Guard rings should go on both sides of the PCB, imho.

I agree, what is R13 ?  I'd use a jumper or low value
resistor on the OTHER side of the hold cap as a way to get the signal into
the island...

H^) harry


----- Original Message -----
From: David Ingebretsen <dingebre at 3dphysics.net>
To: 'Oren Leavitt' <obl64 at ix.netcom.com>
Cc: 'synth diy' <synth-diy at dropmix.xs4all.nl>
Sent: Fri, 05 Nov 2010 01:18:01 -0400 (EDT)
Subject: Re: [sdiy] Guard Rings

OK, thank you very much Oren. I think I see how that would be the island in
hold mode. 

David

~~ -----Original Message-----
~~ From: Oren Leavitt [mailto:obl64 at ix.netcom.com]
~~ Sent: Thursday, November 04, 2010 10:25 PM
~~ To: David Ingebretsen
~~ Cc: 'synth diy'
~~ Subject: Re: [sdiy] Guard Rings
~~ 
~~ 
~~ 
~~ On 11/4/2010 10:58 PM, David Ingebretsen wrote:
~~ > Hi all,
~~ >
~~ > I'm still progressing and working on the Steiner Synthasystem.
~~ >
~~ > I have a question. I am laying out the Dual Sample&  Hold/Random
Voltage
~~ > module schematic here:
~~ >
~~ > http://www.xmission.com/~dingebre/SP_Samp_Hold_1.0.pdf
~~ >
~~ > A current PCB layout closeup showing the guard ring such as it is, is
~~ here:
~~ >
~~ > http://www.xmission.com/~dingebre/PCB_part.jpg
~~ >
~~ > In conversations with Nyle, he recommends putting a guard ring around
~~ the
~~ > high impedance sections and tying it to the output of the voltage
~~ follower,
~~ > but I'm struggling trying to figure out what these are.
~~ >
~~ > I've decided it should include the nodes/pads which connect to the two
~~ FETs
~~ > including a couple of resistor pads and the one capacitor pad.
~~ >
~~ > The ring shows as a red line tracing close to the pads of the FETs,
cap,
~~ > resistor, etc. The guard ring is a trace on both sides of the PCB. It
~~ starts
~~ > and ends on the emitter of the voltage follower which (I think) is Q9.
I
~~ > excluded any pads going to ground or power.
~~ >
~~ > First question, is this correct? I put a dashed line around the pads
I'm
~~ > including in the ring on the schematic.
~~ >
~~ > Second, I've read somewhat about guard rings but would love a link to
~~ other
~~ > information so I can understand this so I make an intelligent PCB.
~~ >
~~ > Thanks everyone.
~~ >
~~ > David
~~ >
~~ 
~~ David,
~~ 
~~ Looking at the pdf, you'll want to place the guard ring around the
~~ traces connecting (Q11-S, C5, R13) and (R13, Q7-G). That's your "island"
~~ of high impedance while in "hold" mode. The ring is connected the output
~~ (emitter) of the emitter-follower Q9 which will be at the same potential
~~ but buffered.
~~ Ditto for Q12, C14, R6, Q8.
~~ 
~~ - Oren

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-- 
Harry Bissell & Nora Abdullah 4eva



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