{"id":166,"date":"2008-08-30T08:48:49","date_gmt":"2008-08-30T13:48:49","guid":{"rendered":"http:\/\/www.circuitdesign.info\/2008\/08\/response-to-edaboard-question-how-can-i-deal-with-3rd-hd-in-a-2nd-sigmadelta-modulator\/"},"modified":"2008-11-20T00:34:10","modified_gmt":"2008-11-20T05:34:10","slug":"response-to-edaboard-question-how-can-i-deal-with-3rd-hd-in-a-2nd-sigmadelta-modulator","status":"publish","type":"post","link":"https:\/\/www.circuitdesign.info\/blog\/2008\/08\/response-to-edaboard-question-how-can-i-deal-with-3rd-hd-in-a-2nd-sigmadelta-modulator\/","title":{"rendered":"Response to edaboard question &#8220;How can I deal with 3rd HD in a 2nd SigmaDelta Modulator&#8221;"},"content":{"rendered":"<p>In response to: <a href=\"http:\/\/www.edaboard.com\/viewtopic.php?p=1074391#1074391\">How can I deal with 3rd HD in a 2nd SigmaDelta Modulator<\/a><br \/>\n<img decoding=\"async\" style=\"800px;\" src=\"http:\/\/www.edaboard.com\/files-eboard\/2008-08-30_09-23-43_9347.jpg\" alt=\"\" \/><\/p>\n<p><span class=\"postbody\">It\u2019s possible that the OTA is limiting you. Doing a matlab model of the sigma-delta and running it should tell you whether it is a circuit problem or a system-level problem. My hunch is that it\u2019s a system-level problem: the noise-shaping filter doesn\u2019t have enough gain at 24 kHz to suppress the 3rd order distortion.<\/span><\/p>\n<p>Seems like the sigma-delta loop doesn\u2019t have a lot of gain where you want it. I would suggest putting in some noise-transfer zeros (noise-shaping filter poles). This would move the nulls off dc and closer to where you want them. You may need to go to a 3rd-order sigma-delta to do this (one NTF zero at dc and two complex ones at 24 kHz or so).<\/p>\n<p>The other alternative, as stated before, is to improve the linearity of the quantizer: go to a multibit.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>In response to: How can I deal with 3rd HD in a 2nd SigmaDelta Modulator It\u2019s possible that the OTA is limiting you. Doing a matlab model of the sigma-delta and running it should tell you whether it is a circuit problem or a system-level problem. My hunch is that it\u2019s a system-level problem: the [&hellip;]<\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[3],"tags":[19,26,44,59],"class_list":["post-166","post","type-post","status-publish","format-standard","hentry","category-analog-pro","tag-adc","tag-linearity","tag-sigma-delta","tag-snr"],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/poCEy-2G","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts\/166","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/comments?post=166"}],"version-history":[{"count":4,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts\/166\/revisions"}],"predecessor-version":[{"id":427,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts\/166\/revisions\/427"}],"wp:attachment":[{"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/media?parent=166"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/categories?post=166"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/tags?post=166"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}