Voltage Amplification

The graph in Fig. 1 shows the drain (channel) current, I_D as a function of the gate bias voltage E_G for a hypothetical n-channel JFET when no signal is applied to the gate electrode. The drain voltage E_D is assumed to be constant. When E_G is fairly large and negative, the JFET is pinched off, and no current flows through the channel. As E_G gets less negative, the channel opens up, and current begins flowing. As E_G gets still less negative, the channel gets wider, and the current I_D increases. As E_G approaches the point where the source-gate (S-G) junction is at forward breakover, the channel conducts as well as it possibly can. If E_G becomes positive enough so that the S-G junction conducts, the JFET no longer works properly. Some of the current in the channel is shunted through the gate. This is like a garden hose springing a leak.
The best amplification for weak signals is obtained when E_G is such that the slope of the curve in Fig. 1 is steepest. This is shown roughly by the range marked X in the graph. For power amplification, results are often best when the JFET is biased at or beyond pinchoff, in the range marked Y.

Fig. 1. Relative drain current as a function of gate voltage in a hypothetical n-channel JFET.

مواضيع ذات صلة

الحجم النووي Nuclean Size

ربوتات النانو (Nanorobots)

تلسكوبات الأشعة تحت الحمراء والسينية

المقاومة الداخلية المرتفعة لبطارية ليثيوم-ايون

أهمية تقنية النانو (Importance of nanotechnology)

متسعات المرشح على التوالي Filter Capacitors in series

أشباه الموصلات

ظاهرة الحفز الضوئي

مكشاف أشباه الموصلات Semiconductor detector

ميكروسكوبات السليكون

تأثيرات الدفيئة وثقب طبقة الأوزون

مخطط الطاقة لوصلة ال PN