tag:blogger.com,1999:blog-70548926257483136012023-11-26T22:09:29.785+06:00Micro Elctronic CircuitsMicroElctronic Circuits Analysis and DesignUnknownnoreply@blogger.comBlogger2125tag:blogger.com,1999:blog-7054892625748313601.post-52554722208014053732009-03-10T00:10:00.000+06:002017-11-02T18:22:41.158+06:00Frequency Model and Response of FETs & MOSFETs With Bode Plots<div dir="ltr" style="text-align: left;" trbidi="on">
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjB5pNZodbX0RRaE6M2qCwp4bAbje3Gs1ZSrUOLWwKiuSRh_nK1RKtDx819UeFd48a8sXbx9MeTZR_LNs-Q9hpaAQsKSIqRIo6SO_w3hVf9z2mOeawKUaPQCNXgPT8CdeY7tSI-y5bAHes/s1600-h/1.JPG" onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" style="margin-left: auto; margin-right: auto;"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5311259361830785090" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjB5pNZodbX0RRaE6M2qCwp4bAbje3Gs1ZSrUOLWwKiuSRh_nK1RKtDx819UeFd48a8sXbx9MeTZR_LNs-Q9hpaAQsKSIqRIo6SO_w3hVf9z2mOeawKUaPQCNXgPT8CdeY7tSI-y5bAHes/s400/1.JPG" style="float: left; height: 300px; margin: 0pt 10px 10px 0pt; width: 400px;" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><br /></td></tr>
</tbody></table>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiw36HD22GEY1QdIAQRY44sNgeYBS8p7M4kXAftzOZHeBRTvHYKlvEIEIIXHDsOh7roVVwjbke3TyogQGsqttYMGwFmGziFQDUb7XdzJVld2XXsfJhFElZ9ZxPJrnNhwR5lI1eotdolStM/s1600-h/2.JPG" onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" style="margin-left: auto; margin-right: auto;"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5311259341937174770" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiw36HD22GEY1QdIAQRY44sNgeYBS8p7M4kXAftzOZHeBRTvHYKlvEIEIIXHDsOh7roVVwjbke3TyogQGsqttYMGwFmGziFQDUb7XdzJVld2XXsfJhFElZ9ZxPJrnNhwR5lI1eotdolStM/s400/2.JPG" style="float: left; height: 300px; margin: 0pt 10px 10px 0pt; width: 400px;" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><br /></td></tr>
</tbody></table>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhiW80cTntZtjipHQ-eZSpCToTqR8JGJPihenfxlmgSfZvBdhv7mh455Sh5mkgLvWIVnwWUBJItx31FTuq1O9Gd3b84W7t5-iqbXAN-6e-5qJeRd2lvVl2dBB0I6ta6V5UOt2TkwWKAOWI/s1600-h/3.JPG" onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" style="margin-left: auto; margin-right: auto;"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5311259338948074354" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhiW80cTntZtjipHQ-eZSpCToTqR8JGJPihenfxlmgSfZvBdhv7mh455Sh5mkgLvWIVnwWUBJItx31FTuq1O9Gd3b84W7t5-iqbXAN-6e-5qJeRd2lvVl2dBB0I6ta6V5UOt2TkwWKAOWI/s400/3.JPG" style="float: left; height: 300px; margin: 0pt 10px 10px 0pt; width: 400px;" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><br /></td></tr>
</tbody></table>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8N49X6H2IHlBLi2fjFhqdGWOHaPoG2atvSCFRtG7sRMH2clkOrHn50a2pMzFYDLwlSfQ9aROLrFJUOkJcjSRP13l4yg2XYIdb_Io7TcIrEZbIoCieD6R7PlNbRjwGFss2BL2lMTs1ecU/s1600-h/4.JPG" onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" style="margin-left: auto; margin-right: auto;"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5311259328515992850" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8N49X6H2IHlBLi2fjFhqdGWOHaPoG2atvSCFRtG7sRMH2clkOrHn50a2pMzFYDLwlSfQ9aROLrFJUOkJcjSRP13l4yg2XYIdb_Io7TcIrEZbIoCieD6R7PlNbRjwGFss2BL2lMTs1ecU/s400/4.JPG" style="float: left; height: 200px; margin: 0pt 10px 10px 0pt; width: 400px;" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><br /></td></tr>
</tbody></table>
</div>
Unknownnoreply@blogger.com0tag:blogger.com,1999:blog-7054892625748313601.post-17014455968024957682009-03-05T22:04:00.000+06:002017-11-02T18:53:00.930+06:00Frequency Response of BJT Amplifiers<div dir="ltr" style="text-align: left;" trbidi="on">
<div style="text-align: justify;">
All amplifiers typically exhibit a band-pass frequency response as in Figure 1. The cut-off frequency on the low end is usually determined by the coupling and bypass capacitors (if there are no such capacitors the low end extends all of the way to DC). The high frequency limit is typically determined by internal capacitances in the transistor itself.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjH-4G-dx1soTvJZYFn2o0QTX65cwNwI76IcrCXGvbCumbENKg20hmn7BEOnItRgiqKGtHBFMhoaarooTMvVesd-X4GfWpL7K5nltZ-uo7Trlaac0pfOOReRKG2YBhZmZUG1BSFRC5Siic/s1600-h/Frequency+response+amplifier..JPG" onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" style="margin-left: auto; margin-right: auto;"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5309746676449031426" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjH-4G-dx1soTvJZYFn2o0QTX65cwNwI76IcrCXGvbCumbENKg20hmn7BEOnItRgiqKGtHBFMhoaarooTMvVesd-X4GfWpL7K5nltZ-uo7Trlaac0pfOOReRKG2YBhZmZUG1BSFRC5Siic/s400/Frequency+response+amplifier..JPG" style="float: left; height: 180px; margin: 0pt 10px 10px 0pt; width: 400px;" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><br /></td></tr>
</tbody></table>
<h1 style="font-weight: bold;">
<span style="font-size: 100%;">Low frequency response</span></h1>
<div>
</div>
<div style="text-align: justify;">
If an amplifier does not have coupling or bypass capacitors, then in general the low frequency response goes all of the way down to DC. However, as we discussed in class, it is desirable to have these capacitors in the circuit to isolate the amplifiers DC bias point from the outside world.</div>
<div class="MsoNormal" style="text-align: justify;">
<o:p></o:p><br /></div>
<div style="text-align: justify;">
In the most general case (Figure 2), the input and output coupling capacitors lead to a high-pass filter response determined by the resistances they see:<br />
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEipojQpeS54qBW6mFLOLeH1hmFAcDsyfELT2OwCRzhV6w-a_JBr3GBK5_v2KfKkIlyv8WLwbXr1o7qKJ1CN6OmO1WTkti5PdQAQbRSc_12cCOu8Sd7p8zAMmwjXgLISo8x1LYVmWIdnNdg/s1600-h/general+amplifier.JPG" onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" style="margin-left: auto; margin-right: auto;"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5309746682863476434" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEipojQpeS54qBW6mFLOLeH1hmFAcDsyfELT2OwCRzhV6w-a_JBr3GBK5_v2KfKkIlyv8WLwbXr1o7qKJ1CN6OmO1WTkti5PdQAQbRSc_12cCOu8Sd7p8zAMmwjXgLISo8x1LYVmWIdnNdg/s400/general+amplifier.JPG" style="float: left; height: 200px; margin: 0pt 10px 10px 0pt; width: 400px;" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><br /></td></tr>
</tbody></table>
<div class="MsoNormal" style="text-align: justify;">
Where R<sub>i</sub> is the source resistance, R<sub>L</sub> is the load resistance, R<sub>in</sub> is the input resistance for your amplifier and R<sub>o</sub> is the output resistance for your amplifier. These last two are calculated based on the type of amplifier you are working with (See the handout on small signal amplifier calculations).</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<div style="text-align: justify;">
<span style="font-family: "; font-size: 10;"> </span> </div>
<div class="MsoNormal" style="text-align: justify;">
Once you have calculated the frequencies due to C<sub>1</sub> and C<sub>2</sub>, the cutoff is determined by the following rules:</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal">
<o:p> </o:p></div>
<div class="MsoNormal" style="margin-left: 0.25in; text-align: justify; text-indent: -0.25in;">
<!--[if !supportLists]-->1)<!--[endif]-->If the two frequencies are more than a decade apart then f<sub>low2</sub> in Figure 1 (the 3db point of the amp) is simply the higher of the two values.</div>
<div>
</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-align: justify; text-indent: -0.25in;">
<!--[if !supportLists]-->2)If the two frequencies are closer than one decade, then the actual cutoff frequency of the amp is somewhat larger than either of the two calculated frequencies.</div>
<div style="text-align: justify;">
</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-align: justify; text-indent: -0.25in;">
<!--[if !supportLists]-->3)<!--[endif]-->If the amplifier has a bypass capacitor, then it can also influence the cutoff frequency. Typical, emitter bypass capacitors are chosen large enough so that their effects are negligible.<br />
<br /></div>
<div class="MsoNormal">
<o:p> </o:p></div>
<h1 style="font-weight: bold;">
High Frequency Response</h1>
<div class="MsoNormal">
<o:p> </o:p></div>
<div class="MsoNormal" style="text-align: justify;">
As previously stated, the high frequency response of a discrete transistor amp is determined by the internal capacitances of the transistor itself (Figure 3).<br />
<br /></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhmabLqnssX4kOxho_f2Nzzvo7lUGoo63pARtkvJvw7cZ7kdwNdaEJo4j675GlD6bpnTkebtS2kvOaPlrWgKIbl_89R-HYRr-QMxoa5JcAr23RLLIR0AC622lRjaUEeRyj7yLh6s1lK07k/s1600-h/High+frequency+model+of+a+BJT.JPG" onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" style="margin-left: auto; margin-right: auto;"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5309746685747454402" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhmabLqnssX4kOxho_f2Nzzvo7lUGoo63pARtkvJvw7cZ7kdwNdaEJo4j675GlD6bpnTkebtS2kvOaPlrWgKIbl_89R-HYRr-QMxoa5JcAr23RLLIR0AC622lRjaUEeRyj7yLh6s1lK07k/s400/High+frequency+model+of+a+BJT.JPG" style="float: left; height: 107px; margin: 0pt 10px 10px 0pt; width: 400px;" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><br /></td></tr>
</tbody></table>
<div class="MsoNormal" style="text-align: justify;">
If either C<sub>be</sub> or C<sub>oB</sub> short out at high frequencies, then the transistor stops acting as an amplifier and so the response is cut off. The values of C<sub>be</sub> and C<sub>oB</sub> can be found or calculated from the transistor spec sheet. Typically, C<sub>oB</sub> is on the spec sheet and C<sub>be</sub> is calculated from f<sub>T</sub> (the gain-bandwidth product) also found on the spec sheet using:</div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh0seXgC1YllgdE2-W7rY7XN47FRNTVKCSiiv6aFKAy3p3S3D-OgJFF6Qm2MX6WhTdPFqytOOEo10j6dDGOlzfh2JSOkBazbf00aA0YxGvWYecaSK_tiDUz-ThyphenhyphenAGnWCNQiNbvfQsqYhJ0/s1600-h/Common.JPG" onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" style="margin-left: auto; margin-right: auto;"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5309746689162083922" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh0seXgC1YllgdE2-W7rY7XN47FRNTVKCSiiv6aFKAy3p3S3D-OgJFF6Qm2MX6WhTdPFqytOOEo10j6dDGOlzfh2JSOkBazbf00aA0YxGvWYecaSK_tiDUz-ThyphenhyphenAGnWCNQiNbvfQsqYhJ0/s400/Common.JPG" style="float: left; height: 240px; margin: 0pt 10px 10px 0pt; width: 400px;" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><br /></td></tr>
</tbody></table>
</div>
Unknownnoreply@blogger.com0