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<p class="MsoNormal"><span style="color:#1F497D">Always GOOD quality metal film fixed resistors. The noise from trimmers is far more than the LSB of a 16 bit ADC/DAC. If you need to adjust the gain then change the resistor values. And always use the lowest
values you can use without overloading the driving amplifiers so as to reduce Johnson noise.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif";mso-fareast-language:EN-GB">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif";mso-fareast-language:EN-GB"> Synth-diy
[mailto:synth-diy-bounces@synth-diy.org] <b>On Behalf Of </b>Jean-Pierre Desrochers<br>
<b>Sent:</b> 13 February 2021 20:25<br>
<b>To:</b> Synth-diy@synth-diy.org<br>
<b>Subject:</b> [sdiy] ADc & DAC voltage dividers.. fixed or trimmer adjustables ??<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoPlainText"><span lang="FR" style="mso-fareast-language:FR-CA">Hi list,<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="FR-CA" style="color:black"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D">I’m in the process of design for 16 bits ADC/DAC circuits.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D">This circuit will receive a 0-8vdc CV voltage, drop it down to 0-5vdc, process it through a MAX11100 16 bits ADC (reference voltage REF02 +5.00v)<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D">Then process the cpu data out to a LTC2641 16 bits DAC (reference voltage REF02 +5.00v).<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D">The DAC’s 0-5vdc will then be amplified back to 0-8vdc.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D">To keep as much as LSB precision I’m wondering if the voltage dividers<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D">Should be fixed or adjustable..<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D">See the attached schematic. The 5v to 8v amplification on the DAC section<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D">Is made using U19B , R3 & R4 (<b><u>fixed</u></b> gain of 1.6)<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D">And the ADC attenuation is made using U19A, R1, P1, R2. (<b><u>adjustable</u></b> attenuation of 5/8).<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D">What would you use for a 16 bits ADC/DAC transfer like this ?<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D">Fixed resistor values (shown in DAC) or 2 resistors with a center trimmer (shown in ADC)?<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="FR-CA" style="color:#1F497D;mso-fareast-language:FR-CA"><img width="815" height="614" id="Image_x0020_1" src="cid:image001.jpg@01D70253.FDEA4990"></span><span lang="EN-CA" style="color:#1F497D"><o:p></o:p></span></p>
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