2.7 Common emitter amplifier

The common emitter BJT circuit shown in Figure 2.7 has the following hybrid parameters. Input impedance, h _ie, equals 2 10 ³ ohms. Voltage feedback ratio, h _re, equals 4 10 ^?4. Current gain, h _fe, equals 50. Output admittance, h _oe, equals 20 10 ^?6 siemens. Calculate the (a) Z _m, (b) Z _out, (c) ?, and (d) A _v respectively.

Figure 2.7: Common emitter amplifier

Solution:

Since h _oeR _C ? 0.1

1. Z _in = h _ie (R ₁ R ₂) = (2 10 ³) (90 10 ³ 10 10 ³) ohms

   Z _in = (2 10 ³) (9 10 ³) = 1,636 ohms

2. Z _out = (1 / h _oe) R _C = (1/20 10 ^?6) (5.1 10 ³) = 4,628 ohms

3. ? = ?h _fe = ?50

4. A _v = ?(h _feR _C)/Z _in = ?(50 5.1 10 ³)/1,636 = ?156