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Unformatted text preview: Lecture 22 Graphical Analysis We saw the benefit and detractions of using graphical analysis of circuits when we looked at diodes. A similar case is true with the BJT. It is handy to understand the circuit operation But it is too much trouble if we wish to make any serious calculations Unlike the diode, though, we have to make use of two plots together to develop the signal transfer. Graphical Solutions From the first graph we convert from the baseemitter voltage to the current through the base This is then the control input for the second graph The base current, as determined from the previous graph gives us the operating point on this graph. Shifts in the base current result in shifts in this operating point. The Base current The presence of the resistor at the base makes the problem more complicated: The load line for the resistor shifts However this gives us a bigger range of linearity for the input We can see the effective voltage at the gate The output we are interested in is the base current The Output The output is the AC component of the collectoremitter voltage This is set by the collector current and the collector resistor We can see how larger resistances lead to large gains As the base current changes, the V CEI C curve shifts, thus moving the operating point....
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 Summer '10
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 Electronics

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