{"id":117,"date":"2008-08-26T21:19:06","date_gmt":"2008-08-27T02:19:06","guid":{"rendered":"http:\/\/www.circuitdesign.info\/2008\/08\/calibrated-level-shifting-circuit\/"},"modified":"2017-03-26T10:39:36","modified_gmt":"2017-03-26T15:39:36","slug":"calibrated-level-shifting-circuit","status":"publish","type":"post","link":"https:\/\/www.circuitdesign.info\/blog\/2008\/08\/calibrated-level-shifting-circuit\/","title":{"rendered":"Calibrated level-shifting circuit"},"content":{"rendered":"

In response to<\/a>:Watch Full Movie Online Streaming Online and Download<\/a><\/p>\n

\n

Hi all,
\nI came across a dc biasing problem of a homodyne receiver.
\nThe output of the direct conversion mixer is connected to a VGA. The
\nfirst stage of VGA and the output of mixer have different DC biasing
\nvalues. I know common source or source follower could be used to shift
\nthe DC bias. But we will lose the flexibility of tuning the biasing of
\nVGA during experiment.
\nIs there any other means to bias the VGA in this case?
\nthanks<\/p>\n

fz<\/p>\n<\/blockquote>\n

My first reaction is that whenever possible, capacitive coupling should be used. I don\u2019t know the topology of mixer, but in many cases, a dc bias block between the RF amp driving the mixer and the mixer itself can allow the mixer to take on whatever common-mode the post-mixer amplifier (PMA) or VGA in this case<\/span> requires.<\/p>\n

If that\u2019s not possible, a simple circuit can be used to do a calibrated common-mode level shift. Obviously, the source-follower can be used. However, source-followers aren\u2019t generally calibrated to a specific voltage level (the amount of level shift is a VGS<\/sub> of a device, which is difficult to calibrate).<\/p>\n

Instead, I came up with the following circuit:<\/p>\n

<\/p>\n

\"scan0057a\"<\/a><\/p>\n

The output voltage is sensed and the tail current is adjusted by the feedback op-amp to set the desired common-mode output voltage. In this case, we need an op-amp that senses the common mode and does an error-feedback, comparing to the desired common mode, VCM<\/sub>. We could do this two-steps: sense the common-mode by averaging the two output voltages, and then differencing with the desired common mode.<\/p>\n

Instead, a modification of the typical diff-pair can be used to both do the summing of the two outputs and to compare with a reference common mode:<\/p>\n

\"scan0057b\"<\/a><\/p>\n

The above circuit doesn\u2019t have the bandwidth that an open-loop source-follower would have. However, that\u2019s another advantage: it can be used to provide a pole of filtering.<\/p>\n

Any questions? Post in the comments below.<\/p>\n

Technorati Tags: circuit design<\/a>,VGA<\/a>,level shift<\/a>,common mode<\/a>,feedback<\/a>,calibrate<\/a>,bias<\/a><\/div>\n","protected":false},"excerpt":{"rendered":"

In response to:Watch Full Movie Online Streaming Online and Download Hi all, I came across a dc biasing problem of a homodyne receiver. The output of the direct conversion mixer is connected to a VGA. The first stage of VGA and the output of mixer have different DC biasing values. I know common source or […]<\/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":[],"class_list":["post-117","post","type-post","status-publish","format-standard","hentry","category-analog-pro"],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/poCEy-1T","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts\/117","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=117"}],"version-history":[{"count":3,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts\/117\/revisions"}],"predecessor-version":[{"id":1050,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts\/117\/revisions\/1050"}],"wp:attachment":[{"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/media?parent=117"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/categories?post=117"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/tags?post=117"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}