Write a note on closed loop gain of an amplifier.

Q.) Write a note on closed loop gain of an amplifier.

 Subject: electronic devices and circuit

Closed Loop Gain of an Amplifier

Closed loop gain is a crucial concept in the study of amplifiers and is defined as the ratio of the output voltage to the input voltage of an amplifier when it is connected in a feedback configuration. In this configuration, a portion of the output voltage is fed back to the input, which alters the overall behavior and performance of the amplifier.

The closed-loop gain, denoted by GCL, can be mathematically expressed as:

$$ G_{CL} = \frac{V_o}{V_i} \tag{1} $$

where:

  • Vo is the output voltage of the amplifier
  • Vi is the input voltage of the amplifier

By employing negative feedback in an amplifier circuit, the closed-loop gain is modified and several advantages are obtained:

  1. Stability: Negative feedback reduces the sensitivity of the amplifier's gain to variations in component values and circuit parameters, making it more stable and reliable.

  2. Increased Accuracy: It aids in reducing the overall gain error, improving the accuracy of the amplifier.

  3. Linearity: Negative feedback linearizes the input-output characteristics of the amplifier, reducing distortion and improving signal fidelity.

  4. Reduced Sensitivity to Noise: The use of feedback can effectively mitigate the effects of internal amplifier noise and external noise sources on the output signal.

  5. Increased Bandwidth: Properly designed feedback configurations can potentially extend the bandwidth of the amplifier.

The closed-loop gain of an amplifier can be calculated using various methods:

  • Direct Measurement: This method directly measures the output voltage and input voltage of the amplifier when a known input signal is applied. The closed-loop gain is then determined by dividing the output voltage by the input voltage.

  • Voltage Divider Rule: If the feedback network consists of resistors, the closed-loop gain can be calculated using the voltage divider rule. The input and output resistances of the amplifier also play a role in determining the closed-loop gain.

  • Operational Amplifier Gain Equations: For operational amplifiers, specific gain equations are available based on the feedback configuration employed (such as inverting or non-inverting configurations). These equations provide a convenient way to calculate the closed-loop gain.

The closed-loop gain of an amplifier is a fundamental parameter that greatly influences the overall performance and characteristics of the amplifier. By carefully designing the feedback network and selecting appropriate amplifier components, the closed-loop gain can be tailored to meet specific application requirements and optimize the amplifier's functionality.