2.8 Common base amplifier

The common base BJT circuit shown in Figure 2.8 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 _in, (b) Z _out, (c) ?, and (d) A _v respectively.

Figure 2.8: Common base amplifier

Solution:

Since h _oeR _C ? 0.1

1. Z _in = h _ie / (1 + h _fe) R _E = (2 10 ³/51) = 36 ohms

2. Z _out = (1 + h _fe)/h _oe R _C = (51 / 20 10 ^?6) (5.1 10 ³) = 5.1 10 ³ ohms

3. ? = h _fe /(1 + h _fe) = 50/51 = 0.98

4. A _v = (h _feR _C)/h _ie = (50 5.1 10 ³)/(2 10 ³) = 127