In addition, band-limiting a<\/em> & p<\/em> can have deleterious effects on the resulting RF signal. In order to maintain spectral masks (contain the near-in spectrum), multiples of the desired bandwidth need to be preserved in a<\/em> and p<\/em>.<\/p>\n We are essentially taking band-limited signals and decomposing them into wide-band signals (so that we can amplify them efficiently) to then recompose them into a final band-limited signal (I+jQ = a*exp(j*p))<\/p>\n A not-so good example of this bandwidth effect is the case where I=cos(wm*t) & Q=0. Then, the a=|cos(wm*t)| and ph = pi*sgn[cos(wm*t)]:<\/p>\n However, this is not such a good example, since in some cases, this discontinuity in amplitude and phase can be reduced by allowing the amplitude to be positive and negative (i.e. a double-balanced mixer) and transferring the phase reversal from p<\/em> to a<\/em>:<\/p>\n Unfortunately, this cannot be done with a transformer-coupled class-D configuration:<\/p>\n Another problem that plagues power modulators is signal leakage. Normally, the input to a power amplifier (PA) is a replica of its output, only lower in power. If this input then leaks to the output of the PA, no harm is done with respect to spectral masks:<\/p>\n Polar modulators, however, have two inputs: amplitude a<\/em> and phase p<\/em>\u2014neither of which look anything like the desired output.<\/p>\n The amplitude path is generally off-frequency (not with the RF carrier). However, the phase path p<\/em> is<\/strong> modulated with the RF carrier and can leak through to the output. Note that this is a wide-band signal that will screw up the spectral mask:<\/p>\n In effect, this means that the dynamic range of the PA is limited by leakage of the phase signal. Note that this can greatly hinder power control\u2014which I consider to be the true challenge of supply modulation.<\/p>\n I\u2019ve heard for the last 10 years or so that polar modulation will give spectrally-efficient modulation formats (OFDM, CDMA, etc.) the PA efficiency that they so lack nowadays. I agree: polar modulation will give a boost in efficiency\u2014when several problems are solved. Here are the challenges that plague polar modulation<\/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-85","post","type-post","status-publish","format-standard","hentry","category-analog-pro"],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/poCEy-1n","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts\/85","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=85"}],"version-history":[{"count":7,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts\/85\/revisions"}],"predecessor-version":[{"id":244,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/posts\/85\/revisions\/244"}],"wp:attachment":[{"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/media?parent=85"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/categories?post=85"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.circuitdesign.info\/blog\/wp-json\/wp\/v2\/tags?post=85"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"Discontinuity](\"http:\/\/www.circuitdesign.info\/wp-content\/uploads\/2008\/08\/scan0058a.jpg\")
<\/a><\/p>\n<\/a><\/p>\nLeakage<\/h2>\n
<\/a><\/p>\n<\/a><\/p>\n