Voltage gain

Definition

Voltage gain is the ratio of the output voltage to the input voltage in an amplifier circuit, often expressed in decibels (dB). It indicates how much an amplifier increases the input signal and is a critical parameter for assessing amplifier performance. Understanding voltage gain helps in analyzing how different amplifier configurations affect the overall amplification process.

5 Must Know Facts For Your Next Test

1. Voltage gain can be calculated using the formula: $$ A_v = \frac{V_{out}}{V_{in}} $$ where $$ V_{out} $$ is the output voltage and $$ V_{in} $$ is the input voltage.
2. In FET and BJT configurations, the voltage gain is influenced by parameters such as transconductance and load resistance.
3. A high voltage gain indicates that even a small input signal can produce a much larger output, making amplifiers useful for various applications.
4. The voltage gain for common emitter (BJT) and common source (FET) amplifiers can be significantly affected by the choice of biasing and external components.
5. Voltage gain may vary with frequency due to reactive components in the circuit, which can lead to bandwidth limitations in amplifier designs.

Review Questions

• How does voltage gain differ between FET and BJT amplifier configurations, and what factors contribute to these differences?
  • Voltage gain in FET amplifiers is primarily influenced by transconductance and load resistance, while in BJT amplifiers, it is affected by both transconductance and current gain. The inherent characteristics of FETs, such as high input impedance, usually result in higher voltage gains without loading down the source. In contrast, BJTs may have different gain characteristics due to their base current requirements, which impacts how they amplify signals.
• Evaluate how feedback can impact voltage gain in amplifier circuits and provide examples related to FETs and BJTs.
  • Feedback can either increase or decrease voltage gain depending on whether it is positive or negative feedback. Negative feedback tends to stabilize and reduce the voltage gain but improves linearity and bandwidth. For example, in a common emitter BJT configuration, applying negative feedback reduces distortion but results in a lower overall gain. Conversely, certain FET configurations may use positive feedback to enhance specific performance metrics at the risk of stability.
• Analyze the implications of voltage gain variations on circuit design choices for both FET and BJT amplifiers in practical applications.
  • Variations in voltage gain influence circuit design choices significantly because they determine how amplifiers will interface with other components. For instance, if high voltage gain is required for a sensor signal conditioning application, designers might favor FET configurations due to their high input impedance and greater voltage amplification capabilities. On the other hand, for applications needing low distortion and wider bandwidths, BJT configurations might be preferred despite potentially lower gains. These design considerations ensure that the amplifier meets specific requirements of the overall system.

Related terms

Decibel: A logarithmic unit used to express the ratio between two values, commonly used to measure voltage gain.

Input Impedance: The impedance presented by an amplifier at its input terminals, affecting how much of the input signal is delivered to the amplifier.

Feedback: A process where a portion of the output signal is returned to the input, influencing the performance and stability of an amplifier.