Amplifiers

Understanding Amplifiers

  • An amplifier is an electronic component meant to increase the power of an input signal.
  • The primary parameters that describe an amplifier include gain, bandwidth, efficiency, linearity, noise, and output dynamic range.
  • The amplifier gain is the ratio of the output signal power to the input signal power and is usually measured in decibels (dB).
  • Bandwidth refers to the range of frequencies over which the amplifier performs adequately.
  • Linearity of an amplifier denotes its ability to amplify the input signal without any distortion.
  • Output dynamic range refers to the difference in dB between the largest and smallest useful output levels.

Classes of Amplifiers

  • Amplifiers are categorised into several classes such as class A, B, AB, and C, based on their configuration and mode of operation.
  • Class A amplifiers conduct over the entire range of the input cycle and are known for excellent linearity but poor efficiency.
  • Class B amplifiers conduct only over one-half of the input cycle, resulting in better efficiency but poorer linearity compared to class A.
  • Class AB amplifiers are a compromise between class A and B, offering improved efficiency with reasonably good linearity.
  • Class C amplifiers conduct less than one-half of the input cycle, which leads to high efficiency but poor linearity.

Positive and Negative Feedback

  • Feedback is a process where a fraction of the output signal is fed back to the input of the amplifier.
  • Positive feedback amplifies the input signal further, resulting in potential instability.
  • Negative feedback reduces the gain and distortion, improves the bandwidth, and stabilises the amplifier.

Operational Amplifiers

  • An operational amplifier, commonly known as an op-amp, is a high-gain amplifier with differential inputs and a single-ended output.
  • An ideal op-amp offers infinite gain and bandwidth, zero output impedance, and infinite input impedance, among others.
  • Real-world op-amps deviate from these ideal characteristics, and it is essential to understand these differences.
  • Op-amps can be configured in multiple ways to serve as inverters, non-inverters, adders, subtractors, integrators, differentiators, and more.

Biased Amplifiers

  • Biasing is a method used to establish a predetermined voltage or current in an amplifier.
  • Different types of biasing techniques are prevalent, including fixed bias, collector-to-base bias, and self-bias.
  • The aim of biasing is to ensure that the amplifier operates in the active region over the entire input signal cycle, to avoid distortion.

Importance of Cooling in Amplifiers

  • Amplifiers generate heat during operation, particularly class A and B amplifiers.
  • Cooling methods are implemented to prevent overheating and ensure reliable and extended use of the amplifier.
  • Cooling techniques used include heat sinks, fans, and liquid cooling systems.

Power and Audio Amplifiers

  • Power amplifiers are used primarily for driving loads like loudspeakers, requiring significant amounts of power.
  • Audio amplifiers are capable of amplifying frequencies within the human hearing range (approx. 20 Hz to 20 kHz).
  • Ensuring correct impedance matching is crucial in such systems to maximise power transfer and avoid potential damage.