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Amplifier (electronic amplifier) – an electronic device designed to produce a signal with a larger amplitude (signal gain) at the output, which is proportional to the input signal. This is possible and happens at the expense of the energy consumed by the amplifier from an external power source.
The efficiency of amplification of the input signal by the amplifier is measured by the gain of this amplifier, which is the ratio of the output voltage, current or power signal to the input signal. Each amplifier has its own, corresponding gain factor value. Amplication of the signals is a fundamental phenomenon in electronics, on which a large majority of existing electronic devices are based. We can say, that an amplifier is a circuit that has a power gain value greater than 1.
Electronic Amplifiers as Integrated Circuits
The internal design of the amplifiers is based on the use of active electronic components – earlier electron lamps, nowadays – mainly transistors. Amplifiers may act as the autonomous devices (Fig. 1) or be in the form of the integrated circuits (Fig. 2), which are implemented inside another device as its components (functional blocks of the whole device’s system).
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Electronic Amplifiers – Division
The division of amplifiers can be made due to various factors.
Amplifier Division due to the Manufacturing Technology
Amplifiers can be divided due to the technology of execution:
- Monolithic systems (up to 30W of power) – produced on a substrate made of silicon monocrystal. Increasing of the output power is at the expense of the quality of the output signal,
- Hybrid systems (up to 200W of power) – have a higher quality of performance and can give much more output power compared to monolithic systems. They are manufactured in layered technology, which is much more expensive than the one used to produce monolithic systems.
Electronic Amplifier Division due to the Amplified Signal Parameter
Due to the amplified signal paremeter, amplifiers can be divided into:
- Current amplifiers (Voltage Gain factor is equal to 1),
- Voltage amplifiers (Current Gain factor is equal to 1),
- Power amplifiers (can simultaneously amplify current and voltage) – the most commonly used in the field of electroacoustics to enhance the acoustic signal. At the input of the power amplifier goes the signal fed from the preamplifier output, which was previously amplified there.
Electronic Amplifier Division due to the type of Amplified Signal
Due to the type of amplified signal, amplifiers can be divided into:
- Constant-current amplifiers (or low-frequency amplifiers),
- Band amplifiers – they can amplify the signals of a certain frequency range:
- Narrowband amplifiers (Tuned amplifiers) – a type of band amplifier, which can amplify the signals of a narrow frequency range (only one frequency e.g. 1kHz or desired frequency range, e.g. 100Hz – 1kHz),
- Wideband amplifiers – a type of band amplifier, which can amplify the signals of a wide frequency range, e.g. 100Hz – 50kHz).
Amplifiers can also be divided due to their physical location in the signal chain, e.g. the preamplifier can amplify the signal, which will then be used and processed in the next device, e.g. in a power amplifier.
Electronic Amplifiers – The Most Important Parameters
Amplifier parameters are determined based on the properties and dependencies describing their input and output signals. Each amplifier has its own gain value. It is a multiplication factor that binds the magnitude of some property of the output signal with the property of the input signal.
One of the most important electrical parameters of amplifiers are:
- Current Amplification Factor (Ai) – the ratio of output current to input current
- Voltage Amplification Factor (Av) – the ratio of output voltage to input voltage
- Power Amplification Factor (Ap) – the ratio of output power to input power
- Input resistance (impedance) Zin – determines how much the amplifier overloads the signal source (the higher – the better),
- Output resistance (impedance) Zout – determines how much of the amplified signal is lost in the amplifier circuits (the smaller – the better),
- Frequency Bandwidth (BW) – the width of the useful frequency range,
- Efficiency – described by the ratio between the output power and total power consumption,
- Linearity of the amplifier – most amplifiers are designed to be linear (to provide constant gain), except applications, where variable gain is desired e.g. ultrasound, radar or speech analysis.
- Signal-to-Noise Ratio (S/N Ratio) – describes a comparison between the level of a desired signal to the level of background noise.
Electronic Amplifiers – Applications
In most cases, amplifiers have been designed to function well in a desired, specific application e.g.:
- High-Fidelity (Hi-fi or Hifi) stereo equipment,
- RTV transceivers (Radio and Television transmitters and receivers),
- Microcomputers and other digital devices,
- Guitar amplifiers and other, various instrument amplifiers.