![\"\"](\"https:\/\/www.circuitdesign.info\/blog\/wp-content\/uploads\/2008\/11\/scan0080.jpg\")
<\/figure>\n\n\n\u00a0<\/p>\n
This LNA consists of an input at the source of the MOS transistor (or emitter of a BJT) , a current-source to bias the transistor, and a resistor load. This configuration is typically used in broadband receivers (cable tuners, TV tuners, software-defined radio).<\/p>\n
The gain of this stage is Av<\/sub> = gm<\/sub>\u00d7R1<\/sub>. This seems like a reasonable stage to produce a gain and therefore overcome noise.<\/p>\n Each of these circuits is presented as a single-ended version. However, there is absolutely no reason not to implement them as differential circuits. I merely draw them single-ended here to get the point across without obfuscating the primary ideas. If there is interest in seeing what the differential versions look like, please post a request in the comments section.<\/span><\/p>\n However, consider what happens when we couple this LNA into a CMOS switch-mode mixer:<\/p>\n Consider the loss term R1\/(R1<\/sub> + R2<\/sub>). It doesn\u2019t have to be there.<\/p>\n If we replace R1 with a current-source load and merely omit R2, we\u2019d have something like this:<\/p>\n Due to the high output impedance of the LNA, a common-mode feedback circuit is necessary. I have detailed two<\/a> ways<\/a> of doing that.<\/p>\n Matt Miller<\/a> and I came up with these ideas at Motorola in 2004. We were not the only ones. Other people within Motorola came up with the same idea. In addition, I had seen it published somewhere around 2004\u2014I thought by Michiel Steyaert or Thomas Lee. Despite my recollection, the closest references I have seen available are: \u201cA 72mW CMOS 802.11a direct conversion receiver with 3.5dB NF and 200kHz 1\/f noise corner\u201d<\/a> (albeit using an inductor load instead of PMOS loads) and \u201cA 1 V 1.1 GHz CMOS integrated receiver front-end\u201d<\/a> (with a folded Gilbert cell mixer).<\/p>","protected":false},"excerpt":{"rendered":" In this post, I will show an evolution of a trans-conducting LNA (rather than a voltage-gain LNA). This is a prime example of current-mode circuit design, which has benefits in terms of linearity\u2014especially for low-voltage scaling in RFCMOS design.<\/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-317","post","type-post","status-publish","format-standard","hentry","category-analog-pro"],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/poCEy-57","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts\/317","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=317"}],"version-history":[{"count":2,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts\/317\/revisions"}],"predecessor-version":[{"id":1160,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts\/317\/revisions\/1160"}],"wp:attachment":[{"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/media?parent=317"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/categories?post=317"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/tags?post=317"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}CMOS LNM employing voltage-mode LNA<\/h2>\n
![\"scan0081\"](\"https:\/\/www.circuitdesign.info\/blog\/wp-content\/uploads\/2008\/11\/scan0081.jpg\")
<\/a> The \u2297 symbol represents a set of commutating MOS mixers, typically capacitively coupled, to separate the dc bias voltages at the output of the LNA and the input of the post-mixer amplifier (PMA). You can essentially ignore then in this analysis, and just assume that they ideally convert from RF to baseband (direct conversion).<\/p>\nTrans-conducting LNA<\/h2>\n
<\/a> You\u2019ll note that the previous loss term is now gone. We have greatly enhanced the gain at essentially no cost. Furthermore, the resulting architecture is even more linear: there is little swing at the output of the LNA; the summing junction of the PMA linearizes the LNA by presenting a low impedance to the LNA.<\/p>\nReferences<\/h2>\n