Gain Factors

Author: Leonard Krugman

Since the current gain a = i_c/i_e of the junction transistor is always less than one, it might be expected that its voltage gain will be less than that of the typical point-contact transistor. In an actual case, however, the voltage gain of the junction transistor is considerably larger than that of the point-contact type. Since the voltage gain is the product of the current gain and the resistance gain, it must be expected that the resistance gain is large. Typical values of emitter input and collector output resistances are 500 ohms and 1 megohm, respectively. Thus, the voltage gain

VG = ar₀/r₁ = 0.951000000/500 = 1900

PG = a²r₀/r₁ = (0.95)²1000000/500 = 1805

The high voltage and power gains of the junction transistor as compared to the point-contact transistor are due primarily to the high collector resistance.