For a circuit as in Fig. 11 and the following circuit...

For a circuit as in Fig. 11 and the following circuit values, calculate the circuit gain and the input and output impedances with and without feedback: $R_{B}=600 \mathrm{k} \Omega, R_{E}=1.2 \mathrm{k} \Omega, R_{C}=$ $4.7 \mathrm{k} \Omega$, and $\beta=75$. Use $V_{C C}=16 \mathrm{~V}$.

Key Concepts

Voltage Gain Calculation in Transistor Amplifiers

Calculating the voltage gain of a transistor amplifier typically relies on the resistor network and the small-signal parameters, where the gain can be expressed as the ratio of the collector load resistor to the effective emitter resistance (which includes contributions from both the emitter resistor and the intrinsic emitter resistance). This calculation can be performed considering both the cases with and without the influence of feedback.

Small?Signal Analysis

This concept involves linearizing a transistor’s nonlinear behavior around a given operating (bias) point to derive a simplified equivalent circuit. The model includes parameters like transconductance and internal resistances, which are essential for calculating voltage gain, as well as input and output impedances in amplifier circuits.

Emitter Degeneration

Emitter degeneration is the practice of including a resistor in series with the emitter of a transistor. This resistor provides local negative feedback, which stabilizes the amplifier’s gain, increases its linearity, and significantly influences both the input and output impedances by raising the effective input resistance and lowering the output resistance.

Negative Feedback in Amplifiers

Negative feedback occurs when a portion of the output is fed back into the input in a way that opposes the input signal. In transistor amplifiers, such feedback (for example, through emitter resistor feedback) not only stabilizes the gain against variations in transistor parameters but also alters impedance characteristics, often leading to improved performance.

Input and Output Impedance Analysis

Determining the input and output impedances of an amplifier involves analyzing how the external resistive network and intrinsic transistor resistances interact. The presence of emitter feedback (degeneration) affects these impedances by increasing the input impedance due to the amplified effect of the emitter resistor at the base and by decreasing the output impedance through the buffering effect of the transistor’s gain.

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