For the common-base configuration of Fig. 18 , the dc...

For the common-base configuration of Fig. 18 , the dc emitter current is $3.2 \mathrm{~mA}$ and $\alpha$ is $0.99 .$ Determine the following if the applied voltage is $48 \mathrm{mV}$ and the load is $2.2 \mathrm{k} \Omega$. a. $r_{c}$ b. $Z_{i}$ c. $I_{c}$. d. $V_{o}$. e. $A_{v}$ f. $I_{b}$ -

For the common-base configuration of Fig. 18 , the dc emitter current is $3.2 \mathrm{~mA}$ and $\alpha$ is $0.99 .$ Determine the following if the applied voltage is $48 \mathrm{mV}$ and the load is $2.2 \mathrm{k} \Omega$.
a. $r_{c}$
b. $Z_{i}$
c. $I_{c}$.
d. $V_{o}$.
e. $A_{v}$
f. $I_{b}$ -

Key Concepts

Common-Base Amplifier Configuration

This is a transistor amplifier setup where the base terminal is common to both the input and the output. In this configuration, the signal is applied to the emitter and the output is taken from the collector, resulting in a low input impedance and high output impedance. Its behavior differs from common-emitter configurations, particularly in its phase relationships and gain properties.

DC Bias Analysis

DC bias analysis involves setting up the correct quiescent operating point (Q-point) of the transistor by defining the DC currents and voltages. This is crucial in amplifier design to ensure that the transistor operates in the desired region (typically the active region), allowing for linear small-signal amplification.

Small-Signal Analysis

Small-signal analysis linearizes the nonlinear behavior of the transistor around its DC operating point to analyze the amplifier's performance. This includes determining parameters such as input and output impedances, voltage gain, and the effect of resistive loads, by replacing the transistor with its small-signal model.

Transistor Current Gain Parameters (? and ?)

Transistors are characterized by their current gains. In a common-base configuration the parameter ? (alpha) represents the ratio of the collector current to the emitter current. Understanding this parameter is critical for determining how the emitter current divides into the base and collector currents, and it underpins the analysis of the amplifier's behavior.

Dynamic or Small-Signal Emitter Resistance

This refers to the small-signal resistance seen at the emitter, which is inversely proportional to the emitter current. It is key to accurately predict the voltage drop and gain in the small-signal model, and it influences the internal resistance elements in the analysis of the amplifier circuit.

Input and Output Impedance

The input impedance is the resistance seen looking into the emitter in a common-base amplifier, while the output impedance is defined by the transistor’s collector and the connected load. These impedances affect the signal transfer and loading effects on the circuit and are important for designing matching networks between stages.

Voltage Gain and Load Effects

Voltage gain in a common-base amplifier is determined by the ratio of the load resistance to the internal emitter resistance along with other transistor parameters. The small applied signal and the presence of a load resistor affect the overall gain, making it important to analyze how the load interacts with the transistor’s characteristics.

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