Amplifier circuit

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As we have developed dierent models for DC signals (simple large-signal model) and AC
signals (small-signal model), analysis of BJT circuits follows these steps:
DC biasing analysis: Assume all capacitors are open circuit. Analyze the transistor circuit

using the simple large signal mode as described in pages 77-78.
AC analysis:

1) Kill all DC sources
2) Assume coupling capacitors are short circuit. The eect of these capacitors is to set a
lower cut-o frequency for the circuit. This is analyzed in the last step.
3) Inspect the circuit. If you identify the circuit as a prototype circuit, you can directly use
the formulas for that circuit. Otherwise go to step 4.
4) Replace the BJT with its small signal model.
5) Solve for voltage and current transfer functions and input and output impedances (nodevoltage
method is the best).
6) Compute the cut-o frequency of the amplier circuit.
Several standard BJT amplier congurations are discussed below and are analyzed. For
completeness, circuits include standard bias resistors R1 and R2. For bias congurations
that do not utilize these resistors (e.g., current mirror), simply set RB = R1 k R2

Common Collector Amplier (Emitter Follower)
DC analysis: With the capacitors open circuit, this circuit is the
same as our good biasing circuit of page 110 with RC = 0. The
bias point currents and voltages can be found using procedure
of pages 110-112.