Repeat the analysis of Example 11 with ro=40 k Ω. What is the effect on Avmid , fLS, fLC, fLE, a

step 1 Inductance is 40 micro henry capacitance 300 nanophorat when the magnitude scaled by 800 and fre

Repeat the analysis of Example 11 with ro=40 k Ω. What is...

Key Concepts

Coupling and Bypass Capacitor Effects (f_L_S, f_L_C, f_L_E)

Coupling capacitors (at the input and output) and bypass capacitors (often at the emitter) create high-pass filter networks with the associated resistances in the path. These networks have characteristic lower cutoff frequencies: f_L_S relates to the input source coupling, f_L_C pertains to the output or collector coupling, and f_L_E is linked to the emitter bypass capacitor. Each cutoff frequency is determined by the RC time constant of the respective network, and changes in circuit resistances — including contributions from r_o — modify these RC values and, hence, the low-frequency response of the amplifier.

Mid-Band Voltage Gain (A_v_mid)

The mid-band voltage gain is the amplifier’s gain measured in the frequency range where reactive components (capacitors and inductors) can be considered as ideal shorts or opens, effectively not influencing the circuit. This gain is primarily determined by the resistive network and the transistor parameters. Changes in the output resistance, such as setting r_o to 40 k?, can affect the voltage division in the load and possibly reduce the effective gain compared to scenarios with a different r_o.

Resulting (Composite) Lower Cutoff Frequency

The overall lower cutoff frequency of the amplifier is determined by the highest among the individual cutoff frequencies from the different coupling and bypass networks. It defines the frequency below which the gain begins to roll off. Adjustments in any component (for example, a change in r_o influencing the resistive values in the output network) can shift one or more of these cutoff frequencies, thereby altering the composite frequency response of the amplifier.

Small-Signal Transistor Amplifier Analysis

This concept involves representing the transistor and the surrounding circuit elements by their linear small?signal models, where capacitors, resistors, and dependent sources are used to analyze the behavior of the amplifier for AC signals. It is fundamental for determining parameters such as gain, input/output resistances, and frequency response, allowing for the study of how variations in circuit elements—like changes in the transistor’s output resistance—affect overall performance.

Output Resistance (r_o) Impact

Output resistance, denoted as r_o, is an intrinsic parameter of the transistor in its active region that models the finite resistance seen looking into the collector. Its value directly affects the amplifier’s gain, as it interacts with load resistances and other circuit elements. Increasing or decreasing r_o can modify the effective load seen by the transistor’s output, thus altering the mid-band gain and, in some cases, the frequency response due to modified time constants in the circuit.

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