<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Thanks Guy.<div class=""><br class=""></div><div class="">It seems to me like given the noisy environment the DAC works in (on-chip with a processor) anything that can improve the common-mode noise rejection of the DAC outputs would be an improvement, and might be a significant improvement.</div><div class=""><br class=""></div><div class="">I’ll have a look at that Analog link.</div><div class=""><br class=""></div><div class=""><div class="">
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<div><br class=""><blockquote type="cite" class=""><div class="">On 5 May 2021, at 10:42, Guy McCusker <<a href="mailto:guy.mccusker@gmail.com" class="">guy.mccusker@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Yes, it will have an impact, though the circuit is already not perfect because the input impedances to the + and - terminals are different anyway. <div class=""><br class=""></div><div class="">There's a bit of discussion on this in the Analog Devices Linear Circuit Design Handbook, chapter 2.3 where they are advocating/ trying to sell you an instrumentation amp... <a href="https://www.analog.com/media/en/training-seminars/design-handbooks/Basic-Linear-Design/Chapter2.pdf" class="">https://www.analog.com/media/en/training-seminars/design-handbooks/Basic-Linear-Design/Chapter2.pdf</a></div><div class=""><br class=""></div><div class=""><br class=""></div><div class="gmail-clearfix" style="box-sizing:border-box;color:rgb(99,99,99);font-family:Helvetica,Arial,sans-serif;font-size:14px"></div><div class=""> </div></div><br class=""><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, May 5, 2021 at 10:18 AM Tom Wiltshire <<a href="mailto:tom@electricdruid.net" class="">tom@electricdruid.net</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style="overflow-wrap: break-word;" class="">Hi all,<div class=""><br class=""></div><div class="">The dsPIC 33FJ128GP802 uP (and others in the family) includes a 16-bit DAC on the chip. The outputs from the DAC are provided as a differential output to help cancel any noise generated by the uP internally. NOt a bad idea, seeing as that is probably inevitable. Despite this precaution, the DAC is reasonably noisy and not suitable for all applications.</div><div class=""><br class=""></div><div class="">The example circuit for combining the differential outputs is shown attached - a simple diff amp with 10K resistors everywhere.</div><div class=""><br class=""></div><div class="">Now, my question is this:</div><div class=""><br class=""></div><div class="">If I change the gain of the differential amp by increasing R6/R8 (to 47K, say) does this affect the noise cancellation properties of the diff amp?</div><div class=""><br class=""></div><div class="">It seems to me that it might, because the positive input now has a different proportion of signal going to it than the negative input.</div><div class=""><br class=""></div><div class="">Thanks,</div><div class="">Tom</div><div class=""><br class=""></div><div class=""><div class="">
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