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Home Grounded Emitter and Grounded Collector Transistors The Grounded Emitter Connection Output Resistance  
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Output Resistance for the Grounded Emitter ConnectioAuthor: Leonard Krugman The output resistance was defined by equation 321 in terms of the general fourterminal parameters as: The output resistance in terms of the internal transistor parameters in the grounded emitter connection becomes:
Fig. 45. Output resistance vs generator resistance for typical pointcontact transistor (grounded emitter). The effect of the value of the signal generator resistance is illustrated for the pointcontact and junction transistors in Figs. 45 and 46, respectively. Notice that the output resistance of the pointcontact type is positive at R_{g} = 0, and decreases rapidly to zero when R_{g} is slightly less than 50 ohms. As R_{g} is increased further, r_{o} becomes negative and gradually approaches the limiting condition, when R_{g} is infinite, r_{1} = r_{22} = 11,850 ohms. Thus, the pointcontact transistor can have a negative output resistance over a large range of generator resistance values, and this characteristic can be used in transistor oscillator design. Circuits of this type are called "basecontrolled oscillators." Fig. 46. Output resistance vs generator resistance for typical junction transistor (grounded emitter). The output resistance of the junction transistor is always positive, and for the typical type considered, r_{o} gradually decreases from approximately 273,000 ohms to 100,000 ohms as R_{g} is increased from zero to infinity. The range in which both the output and input resistances of the pointcontact transistor are positive can be increased by adding external resistance in the emitter arm. This increases the effective value of r_{e} = r_{12}. Notice that if enough external resistance is added so that the effective emitter resistance r_{e} + R_{L} is equal to or greater than (r_{c}  r_{m}), the input and output resistance is positive. This stabilizing effect of adding resistance to the emitter load is frequently used in transistor circuit applications.


Home Grounded Emitter and Grounded Collector Transistors The Grounded Emitter Connection Output Resistance 