Page 990 - Basic Electrical Engineering

The dc level of the drain voltage is

–3
V = V DD – I × R = 18 – 2.5 × 10 × 5 × 10 3
1
D
D
= 7.5 V
When the positive half cycle of the ac input is flowing, V = +50 mV. For this
i
current,

–6
∆I = Y × v = 5000 × 10 × 50 × 10 –3
fs
i
D
= 0.25 mA
The new drain voltage is

V D = V DD – (I + DI ) R 1
D
D
–3
= 18 – (2.5 + 0.25) × 10 × 5 × 10 –3
= 6.25 V

Thus, V has changed from V = 7.5 V to V = 6.25 V. The change of V D
D
D
D
is equal to –1.25 V For the negative half cycle of input cycle, the change of
V can be calculated as +1.25 V. Thus, we see that for an input voltage
D
variation of ± 50 mV with VG adjusted for ID = 2.5 mA, the output voltage

change obtained is ± 1.25 V. The voltage amplification of the circuit, A is
v

Thus, the input voltage is amplified 25 times.

14.9 MOSFET

MOSFET is one of the most widely used devices incorporated in integrated

circuits (IC). It is a three-terminal device, the three-terminals are drain,
source, and the gate. A MOSFET is also known as insulated gate field effect
transistor (IGFET) as the gate of the MOSFET is insulated from the channel