Concept explainers
Consider the circuit in Figure P6.45. The transistor parameters are
Figure P6.45
a.
The value of the ICQ and VCEQ .
Answer to Problem 6.45P
Explanation of Solution
Given:
The circuit is given as:
Calculation:
Let the BJT be the single node, then by applying Kirchhoff’s current law, the quiescent emitter current
In Common-Emitter mode:
The relation between the quiescent collector current is
For dc analysis,
All the capacitors act as an open circuit and all the ac sources act as short circuits.
DC analysis:
Redrawing the circuit by open circuit, the capacitors, and short circuit the ac sources.
Evaluating the Thevenin resistance
Evaluating the Thevenin voltage,
Drawing the modified circuit:
Applying the Kirchhoff s voltage law in the base-emitter loop,
Substituting
From equation (2):
Substituting
Therefore, the value of
From equation (1) and (2):
Substituting
Substitute
Drawing the modified circuit:
Applying Kirchhoff s voltage law to the loop,
Substituting
Therefore, the value of
b.
To plot: The dc and the ac load lines.
Explanation of Solution
Given:
The circuit is given as:
Calculation:
Applying Kirchhoff s voltage law around the collector-emitter loop in figure 1.
Substitute
Substitute
The required “Q” point co-ordinates are
Draw the DC load line:
Drawing the AC equivalent circuit:
Evaluating the ac load
The expression for the ac load line:
Substitute
Substitute
Drawing the ac load line:
c.
The small signal voltage gain.
Answer to Problem 6.45P
The small signal voltage gain.
Explanation of Solution
Given:
The circuit is given as:
Drawing the small signal analysis of the circuit by short circuiting the dual dc sources and the capacitors:
Evaluating the diffusion resistance,
Evaluating the small signal transistor output resistance
Evaluating the input resistance
Calculate the input resistance
The small-signal voltage gain is,
d.
The output resistance.
Answer to Problem 6.45P
The output resistance is
Explanation of Solution
Given:
The circuit is given as
Calculation:
From equation 5,
Thus, the input resistance
Calculate the output resistance,
Therefore, the output resistance
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