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Voltage Gain VGAuthor: Leonard Krugman Looking again at Fig. 39, it is seen that the voltage gain . Since E_{2} = i_{2}R_{L} and E_{g} = i_{1} (R_{g} + r_{1}),
Since , if equation 38 is substituted for in equation 322 and if equation 313 is substituted for r_{1} in equation 322 the voltage gain becomes:
Notice that the voltage gain is maximum when R_{L} is infinite and Rg is zero. Under these conditions the maximum
For the typical pointcontact transistor, the maximum = 96. Assuming typical values of R_{L} = 25,000 ohms, and R_{g} = 200 ohms For the typical junction transistor, the maximum = 3,450.Assuming typical values R_{L} = 1 megohm, and R_{g} = 200 ohms The power gain (PG) of the transistor can be calculated from the product of the current gain and the voltage gain or found directly from the ratio of output power to input power. PG = α(VG) The theoretical maximum power gain is the maximum current gain and the maximum voltage gain. However, the condition for maximum current gain is R_{L} = 0, and the condition for maximum voltage gain is R_{L} = infinity. Since these conditions are in opposition, the problem of finding the maximum power gain involves matching the input and output resistances of the transistor. The maximum power gain is obtained when the internal resistance of the signal generator is equal to the input resistance of the transistor, and the load resistance is equal to the output resistance of the transistor, that is R_{g} = r_{{} and Rl = ^{r}o When these conditions are simultaneously satisfied, the transistor is image impedance matched.


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