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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D">Hi Pete!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D">You could have a look at the Maxim MAX14759/MAX14761/MAX14763 analog switches:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D"><a href="https://www.maximintegrated.com/en/datasheet/index.mvp/id/7503">https://www.maximintegrated.com/en/datasheet/index.mvp/id/7503</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D">datasheet:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D"><a href="https://datasheets.maximintegrated.com/en/ds/MAX14759-MAX14763.pdf">https://datasheets.maximintegrated.com/en/ds/MAX14759-MAX14763.pdf</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D">1 – 2 ohms
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D">-25…+25V max signal range<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D">3…5V supply range<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D">100MHz bandwidth<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D">Ciao<br>
Peter<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"><a href="http://www.ullrich.at.tt"><span style="color:blue">http://www.ullrich.at.tt</span></a> (My homepage)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"><a href="http://synpro.heimat.eu/datadial.htm"><span style="color:blue">http://synpro.heimat.eu/datadial.htm</span></a>
(Synth addon)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"><a href="http://rc100-usb.at.tt/"><span style="color:blue">http://rc100-usb.at.tt/</span></a> (Roland sampler tool)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="DE" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">Von:</span></b><span lang="DE" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Synth-diy [mailto:synth-diy-bounces@dropmix.xs4all.nl]
<b>Im Auftrag von </b>Pete Hartman<br>
<b>Gesendet:</b> Montag, 27. Juni 2016 16:15<br>
<b>An:</b> synthdiy diy<br>
<b>Betreff:</b> [sdiy] non-mechanical switching solutions<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I have a problem I'm trying to solve....<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">...and let's just assume the problem has to be solved, I can't just redesign around it. In a perfect world ... but that's not where this sits.<br>
<br>
I'm working with a ladder filter, switching 3 different capacitor ranges (Moog 904A, yes?). But I don't have room for a multipole rotary switch of the necessary size. What electronic solutions might I use for this? (and note that while step one is to solve
four poles for the 904A, step 2 will be to solve for the 904C which has a *9 pole* switch, which hopefully can use the same solution)<br>
<br>
If I use an on-off-on switch, pull ups and ground connected to the common, I have three positions giving me 01, 11, and 10 which can be decoded to 3 out of 4 positions on a mux or a decoder. A Mux acting as a switch to put in or out the various capacitor values....<br>
<br>
First thought: CD4052, but that doesn't work well in practice at all.<br>
<br>
Second thought: DG409, better characteristics, but that still doesn't work sufficiently well. <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Dig around a while for why.... aha, the on resistance for both is significant, especially for the capacitive stages of a ladder filter. The DG409 has on the order of 100R - 120R. Too much, and confirmed to
be the issue by comparing physical connections with wire to physical connections with 100R resistors.<br>
<br>
Third thought: MOSFETs have low on resistance.... And an initial test of VN0104's (on resistance on the order of 3R - 5R, much better) shows somewhat more promise. A little concerned about on capacitance and also whether I can get an appropriate Vgs at the
top stage of the ladder (where the source voltage will be on the order of 10V), but so far so good; may need a MOSFET with a lower range for Vgs-on, but the VN0104 is pretty darn good with a max of 2.4V.... that's just at the edge of the spec though, I think,
something better would be nice. Don't want to be in the position of having to "select" working transistors for the top stage.<br>
<br>
So the questions for the assembled brains bigger than mine:<br>
<br>
1) can anyone suggest a better (yet still reasonably common) mosfet with low Vgs and low rds-on?<br>
<br>
2) some other (electronic, not mechanical) solution that would work in this specific instance? Note that while the above description assumes an SPDT switch, I can go up to 2 poles, but not beyond. An on-on-on would also be an option. Toggle switch is a requirement
though.<br>
<br>
Just to repeat; hopefully this isn't necessary in this audience, but some other fora where I occasionally ask questions, I often get offered answers that ignore the constraints I'm trying to fit within (in this case, no mechanical solution, redesigning to use
a physical rotary switch is not an option). "Your constraints are stupid" is not a helpful suggestion, yet you might be surprised how often it comes up :).<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">Thanks...<br>
<br>
Pete</span><o:p></o:p></p>
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