Performance of Amplifier

In the case of common emitter configuration, we have to calculate different parameters of the Amplifier configuration. We have to calculates Voltage, Input Resistant, Output Resistant, Effective Collector load, Current Gain, Voltage Gain, Power gain, Trans Conductance.

Input Resistance R_i

It is defined as the ratio of the negligible change in Base-Emitter voltage to the negligible in the Base Current, at constant Collector-Emitter voltage.

Input Resistance (R_i)= V_BE / I_B

Where,

R_i = input resistance

V_BE= base-emitter voltage

I_B = base current.

Output Resistance R_O

It is defined as the ratio of small change in Collector-Emitter voltage to the small change in collector current at constant base current_B.

Output resistance(R_O) = ΔV_CE / ΔI_C

Where,

R_O = output resistance

V_CE = Collector Emitter Voltage

I_C = Collector current

I_B = Base Current

Effective Collector Load

The load is linked to a transistor’s collector. For a single-stage amplifier, the output voltage is obtained from the transistor’s collector; for a multi-stage amplifier, it is obtained from a transistor circuit’s cascaded stages.

It is, by definition, the entire load as perceived by the collector current of the A.C. The effective collector load for single-stage amplifiers is RC plus Ro combined in parallel.

Effective Collector Load, R_AC = R_C // R_O

R_AC = (R_C×R_O) / (R_C+R_O)

Hence for the Single Stage Amplification Effective load is equivalent to the collector load.

Current Gain

Current gain is the gain in terms of current that is noticed when changes in input and output currents occur. It is, by definition, the relationship between the change in base current (ΔI_B) and the change in collector current (ΔI_C).

β = Current gain,

β = ΔI_C / ΔI_B

ΔI_C = Small Change in collector current.

ΔI_B = Small change in base current.

Voltage Gain

Voltage gain is the amount of voltage gained when variations in input and output currents are noted. It is, by definition, the ratio of the input voltage change (ΔV_BE) to the output voltage change (ΔV_CE).

Voltage gain, A_V = ΔV_CE / ΔV_BE

Power Gain

The gain observe in power output siganl when input signal is passed through the Amplifer is called as Power gain.

A_P = Power gain

A_P = Current gain × Voltage gain

A_P = β × A_V

Although transistors can be used for many other things, amplification is the main application for them. The PN junctions of the transistor must be appropriately biased by external voltages for the transistor to function as an amplifier. The transistor operates in three distinct modes: Active, Saturation, and Cutoff, depending on the external bias voltage polarities that are applied. An amplifier is only functional in the active mode of the transistor. Transistors can be employed as amplifiers in addition to switches.

A three-layer semiconductor device with amplifier capabilities is called a transistor. The transistor can regulate a greater signal flow between the collector and emitter by applying a small signal to the base. This makes transistors valuable in electronic circuits as amplifiers for music, radio signals, and more. The development of modern technology has been significantly influenced by the transistor’s capacity to amplify signals. In essence, transistors are amplifiers used for amplification. “Amplification” is the process of increasing a weak signal’s amplitude without altering its frequency or form. ‘Transistor biasing’ is the process of accomplishing this by having the transistor’s input circuit remain forward-biased and its output circuit remains reverse-biased throughout the whole signal. The weak signal is received by the transistor’s base, and an amplified output is produced by the collector circuit. The signal must only increase in strength and not change in shape for amplification to occur.