Electronic amplifiers

CMOS Introduction
CMOS Amplifier
Amplifier characteristics
Gain
Output dynamic range
Bandwidth and rise time
Settling time and aberrations
Slew rate
Noise
Efficiency
Linearity
Electronic amplifiers
Two-Stage Amplifier
Design  Of  OP-AMP
Design Of Two Stage OP-AMP




There are many types of electronic amplifiers for different applications.

One common type of amplifier is the electronic amplifier, commonly used in radio and television transmitters and receivers, high-fidelity ("hi-fi") stereo equipment, microcomputers and other electronic digital equipment, and guitar and other instrument amplifiers. Its critical components are active devices, such as vacuum tubes or transistors.

 

Electronic amplifier classes

Amplifiers are commonly classified by the conduction angle (sometimes known as 'angle of flow') of the input signal through the amplifying device.

Class A

 

Where efficiency is not a consideration, most small signal linear amplifiers are designed as Class A, which means that the output devices are always in the conduction region. Class A amplifiers are typically more linear and less complex than other types, but are very inefficient. This type of amplifier is most commonly used in small-signal stages or for low-power applications (such as driving headphones).

 

 

 

Class B

In Class B, there are two output devices (or sets of output devices), each of which conducts alternately for exactly 180 deg (or half cycle) of the input signal. 

Class AB

 

Class AB amplifiers are a compromise between Class A and B, which improves small signal output linearity; conduction angles vary from 180 degrees upwards, selected by the amplifier designer. Usually found in low frequency amplifiers (such as audio and hi-fi) owing to their relatively high efficiency, or other designs where both linearity and efficiency are important (cell phones, cell towers, TV transmitters).

Class C

 

Popular for high power RF amplifiers, Class C is defined by conduction for less than 180 of the input signal. Linearity is not good, but this is of no

 

Significance for single frequency power amplifiers. The signal is restored to near sinusoidal shape by a tuned circuit, and efficiency is much higher than A, AB, or B classes of amplification.

 

  

Class D

 

These use switching to achieve a very high power efficiency (more than 90% in modern designs). By allowing each output device to be either fully on or off, losses are minimized. A simple approach such as pulse-width modulation is sometimes still used; however, high-

performance switching amplifiers use digital techniques, such as sigma-delta modulation, to achieve superior performance. Formerly used only for subwoofers due to their limited bandwidth and relatively high distortion, the evolution of semiconductor devices has made possible the development of high fidelity, full audio range Class D amplifiers, with S/N and distortion levels similar to their linear counterparts

Power Amplifier

 

The term "power amplifier" is a relative term with respect to the amount of power delivered to the load and/or sourced by the supply circuit. In general a power amplifier is designated as the last amplifier in a transmission chain and is the amplifier stage that typically requires most attention to power efficiency. For these reasons, a power amplifier is typically any of the above-mentioned classes except Class A.

 Transistor amplifiers

The essential role of this active element is to magnify an input signal to yield a significantly larger output signal. The amount of magnification (the "forward gain") is determined by the external circuit design as well as the active device.

 

Many common active devices in transistor amplifiers are bipolar junction transistors (BJTs) and metal oxide semiconductor field-effect transistors (MOSFETs).

 

Applications are numerous; some common examples are audio amplifiers in a home stereo or PA system, RF high power generation for semiconductor equipment, to RF and Microwave applications such as radio transmitters.

Transistor-based amplifier can be realized using various configurations: for example with a bipolar junction transistor we can realize common base, common collector or common emitter amplifier; using a MOSFET we can realize common gate, common source or common drain amplifier. Each configuration has different characteristic (gain, impedance...).

 

 

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