56 lines
2.2 KiB
HTML
56 lines
2.2 KiB
HTML
<title>Common-Source Amplifier</title>
|
|
<link rel="SHORTCUT ICON" href="favicon.ico">
|
|
<body>
|
|
<hr>
|
|
<table><tr><td>
|
|
<iframe width=640 height=500 src="http://127.0.0.1:8888/circuitjs.html?startCircuit=http://www.falstad.com/circuit-java/circuits/mosfetamp.txt"></iframe>
|
|
</td><td width="20"> </td><td valign="top">
|
|
</td>
|
|
</tr></table>
|
|
<p>
|
|
This is a <a href="http://en.wikipedia.org/wiki/Common_source">common-source</a>
|
|
amplifier, which amplifies the input voltage about 30 times.
|
|
<p>
|
|
The gain of this amplifier is determined partly the
|
|
<a href="http://en.wikipedia.org/wiki/Transconductance">transconductance</a>
|
|
of the
|
|
<a href="http://en.wikipedia.org/wiki/MOSFET">MOSFET</a>. This depends on
|
|
the bias point in the circuit;
|
|
here it averages about 9 mA/V. This means that a change in the gate voltage
|
|
causes a change in the drain current that is 9 mA/V times the gate voltage
|
|
change.
|
|
<p>
|
|
The drain current goes through a 4k ohm resistor. The capacitor connected
|
|
to the source is supposed to act as a short circuit at the input frequency,
|
|
so it and the source resistor can be ignored.
|
|
A change in input of 50 mV causes a change in drain voltage of 9 mA/V * 50 mV *
|
|
4000 ohms, or about 1.8 V. This means the predicted output gain is
|
|
36. Here it is less
|
|
because the transconductance changes over the input cycle (the amplifier
|
|
isn't quite linear), we are ignoring the output resistor, and the source
|
|
capacitor isn't quite a short circuit like we supposed.
|
|
|
|
<p>
|
|
Next: <a href="e-cmosinverter.html">CMOS Inverter</a><br>
|
|
Previous: <a href="e-mosmirror.html">Current Mirror</a><br>
|
|
<a href="e-index.html#mosfetamp">Index</a><br>
|
|
<a href="index.html">Simulator Home</a><br>
|
|
<hr>
|
|
<script type="text/javascript"><!--
|
|
google_ad_client = "pub-1974179407250396";
|
|
/* 728x90, created 7/9/08 */
|
|
google_ad_slot = "3265434789";
|
|
google_ad_width = 728;
|
|
google_ad_height = 90;
|
|
//-->
|
|
</script>
|
|
<script type="text/javascript"
|
|
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
|
|
</script>
|
|
<hr>
|
|
<a href="http://www.falstad.com/mathphysics.html"><img src="/mathphysics_small.gif"></a>
|
|
<a href="http://www.falstad.com/index.html"><img src="/me_small.gif"></a>
|
|
<br><i>java@</i><i>falstad.com</i>
|
|
<br>Generated Sun Jul 24 2016
|
|
</body>
|