Electronic Amplifier

The electronic amplifier is a circuit or element that provides gain. Amplifiers are used to provide a number of functions:

  • Increase or attenuate magnitude of a physical quantity.
  • Transform signals from one physical variable to another (e.g. charge to voltage).
  • Remove DC biases.
  • Provide impedance matching.

Care should be taken to ensure:

  • Linearity.
  • Satisfactory frequency response.
  • Satisfactory ‘slew rate’ i.e. response to maximum rate of rise of a signal.

Types:

  • Voltage amplifier
  • Charge amplifier
  • Differential amplifier
  • Pre-amplifier

Amplification Factor – The voltage gain of an amplifier with no load on the output. Symbol: MU

Audio Amplifier – an amplifier designed specifically for amplifying audio signals in the frequency range 20Hz to 20kHz.

Classes of Amplifier

  • Class A: An amplifier so designed that the bias is set on the linear portion of the characteristic curve and in which the input signal amplitude is confined to the linear operating region.
  • Class AB1: Amplifier with slightly higher bias than the Class A and with a larger input signal having amplitudes reaching (but not exceeding) the cutoff and positive regions of grid-signal swing.
  • Class AB2: An amplifier with higher bias than the Class AB1 and with grid signal excursions extending into the cutoff and positive tube characteristic regions.
  • Class B: An amplifier with bias at or near the tube cutoff point. Positive alternations of the input signal cause current flow.
  • Class C: An amplifier biased beyond the cutoff point so current flows for only a portion of the positive alternations of the input signal.
  • Class D: A switching amplifier or PWM amplifier, the switches are either fully on or fully off, significantly reducing the power losses in the output devices.

Direct Current Amplifier – a direct coupled amplifier that can provide gain for zero-frequency signals.

Instrumentation Amplifier – a circuit whose output voltage with respect to ground is proportional to the difference between the voltages at its two inputs.

Noise Figure – The ratio of the noise power in the output of an amplifier to that part of the output noise power that is due solely to the noise in the input signal.

Nondegenerative Parametric Amplifier – A parametric amplifier that uses a pump signal frequency that is higher than twice the frequency of the input signal.

Operational Amplifier

One of the basic building blocks of analogue circuits – a high gain stable amplifier with a voltage gain of 100 to 100,000 or more. Operational amplifiers are widely used for signal processing and computational work.

Non-Inverting Amplifier – the signal is amplified but the positive portion of the signal remains positive at the output. The negative portion of the input signal remains negative at the output.

Non-inverting operational amplifier

Inverting Amplifier – the positive part of the input signal is negative and amplified at the output. The negative part is amplified and becomes positive.

inverting amplifier

Differentiating Amplifier – the output is the differential of the input signal with respect to time.

differentiating amplifier

Integrating Amplifier – the output signal is the integration of the input signal.

Integrating amplifier

Peaking Coil – an inductor used in an amplifier to provide high-frequency compensation, which extends the high-frequency response of the amplifier.

Power Amplifier – an amplifier in which the output-signal power is greater than the input-signal power. Typical figures of merit include gain, efficiency and linearity (in amplitude and phase modulated systems) and stability.

Preamplifier – an amplifier that raises the output of a low-level source for further processing without appreciable degradation of the signal-to-noise ratio.

Push Pull Amplifier – an amplifier that uses two transistors whose output signals are in phase opposition.

Quiescent Operating Point – the zero-signal voltage and current values in a circuit or amplifier.

Reactance Amplifier – a low-noise amplifier that uses a nonlinear variable reactance as the active element instead of a variable resistance. Also called a Parametric Amplifier.

RF Amplifier – an amplifier designed to amplify signals with frequencies between 10 kilohertz and 100000 megahertz.

Voltage Amplifier – an amplifier in which the output-signal voltage is greater than the input-signal voltage.

Wideband Amplifier – an amplifier designed to pass an extremely wide band of frequencies, such as a video amplifier.

References

  1. Operational Amplifier Basics – an electronics-tutorials.ws tutorial on opamps.

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