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Date: 2-5-2021
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Transconductance
Recall the discussion of dynamic current amplification from the last chapter. This is a measure of how well a bipolar transistor amplifies a signal. The JFET analog of this is called dynamic mutual conductance or transconductance.
Refer again to Fig. 1. Suppose that EG is a certain value, with a corresponding ID resulting. If the gate voltage changes by a small amount dEG then the drain current will also change by a certain increment dID. The transconductance is the ratio dID/dEG. Geometrically, this translates to the slope of a line tangent to the curve of Fig. 1.
The value of dID/dEG is obviously not the same everywhere along the curve. When the JFET is biased beyond pinchoff, in the region marked Y in the figure, the slope of the curve is zero. There is no drain current, even if the gate voltage changes. Only when the channel is conducting will there be a change in ID when there is a change in EG. The region where the transconductance, dID/dEG, is the greatest is the region marked X, where the slope of the curve is steepest. This is where the most gain can be obtained from the JFET.
Fig. 1: Relative drain current as a function of gate voltage for a hypothetical N-channel JFET
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علامات بسيطة في جسدك قد تنذر بمرض "قاتل"
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أول صور ثلاثية الأبعاد للغدة الزعترية البشرية
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العتبة الحسينية تطلق فعاليات المخيم القرآني الثالث في جامعة البصرة
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