2.11 Common gate amplifier

The common gate FET circuit shown in Figure 2.11 has the following parameters. Forward transadmittance, y _fs, equals 1.5 10 ^?3 siemens. Output conductance, y _os, equals 10 10 ^?6 siemens. Gate-to-source resistance, r _gs, equals 1 10 ⁸ ohms. Gate-to-drain resistance, r _gd, equals 1 10 ⁸ ohms. Calculate the (a) Z _in, (b) Z _out, and (c) A _v respectively.

Figure 2.11: Common gate amplifier

Solution:

r _d = 1/y _os = 1 10 ⁵ ohms

g _m = y _fs = 1.5 10 ^?3

? = y _fsr _d = g _mr _d = 1.5 ^?3 1 10 ⁵ = 150

1. Z _in = (r _d + R _D)/( ? + 1) R _s

   Z _in = (1.1 10 ⁵/151) (1.5 10 ³) = 728 (1.5 10 ³) = 490 ohms

2. Z _out = [r _d ( ? + 1)R _s] R _D = [1 10 ⁵ + (151)1.5 10 ³] (1 10 ⁴)

   Z _out = (3.265 10 ⁵) (1 10 ⁴) = 9,969 ohms

3. A _v = ( ?