Page 989 - Basic Electrical Engineering

voltage change across the device, i.e., VD. The ratio of the output voltage to
the input voltage is called voltage amplification of the circuit, A .
v

Figure 14.27 (a) I versus V DS characteristics for variable V GS of a JFET; (b) I versus V GS
D
D
characteristics (also called transfer characteristic) for a JFET
Example 14.5 In an FET voltage amplifier circuit as shown in Fig. 14.28,

an input voltage of ± 50 mV is applied. Calculate the voltage gain of the
amplifier. The following are given:

Figure 14.28 A voltage amplifier circuit using an FET

VDD = 18 V, R = 5 kΩ, V is so adjusted that I is 2.5 mA.
G
D
1
Forward transfer admittance of the FET, Y = 5000 μS
FS

Solution:

We have to calculate the output voltage change for an input of ± 50 mV.