Amplifiers (amps) are tiny components found in hearing aids to make voices sound louder. You can also find a variety of amplifier components in radios to boost faraway signals, in stereo equipment to drive loudspeakers, and in the huge boxes musicians plug into electric guitars to raise the roof.
But what are amplifiers, and how can they help engineers? Let’s take a closer look.
What Is an Amplifier?
An amplifier is an electronic component (electromagnetic) that boosts electric current. It’s a generic term that describes circuits that produce an increased version of an input signal. A signal amplifier has three main properties:
- Input resistance (RIN)
- Output Resistance (ROUT)
- Gain or amplification (A)
History and Evolution of Amplifiers
The father of the amplifiers is Lee de Forest, an American physicist and electronics engineer. In 1906, while working in radio (then called wireless telegraphy), Lee filed a patent for a device he described as “to amplify feeble electric currents.” The device, called the Audion, became an essential component of radio receivers.
Later, others (notably Edward Armstrong and Irving Langmuir) turned the Audion into a practical device. Then in 1947, John Bardeen, William Shockley, and Walter Brattain developed the “solid-state” transistor leading to portable and highly reliable amplifiers (packaged as single chips) after the invention of integrated circuits in the late 1950s.
Types of Amplifiers
Amplifiers are categorized into different types based on their function or the type of signal they amplify. Below are the different types of amplifiers.
1. Power Amplifiers
They increase the magnitude of voltage, power, and current of an input signal, such as those used in transmitters. However, they amplify only a part of the AC signal applied to amplifiers. Hence, the different classes of amps (A, B, AB, C, and D) depend on the portion of wave amplified.
2. Operational Amplifiers
These high-gain electronic voltage amplifiers perform mathematical operations on voltages. They have two input terminals, and their uses include inverting and non-inverting amplifiers, difference amplifiers, summing amplifiers, etc.
3. Audio Amplifiers
They reproduce input audio signals at the desired volume and power levels of sound-producing output elements. They are used in loudspeakers, headphones, and other sound systems such as home audio, public address, and guitar amplifiers.
4. Voltage Amps
These are the most common amps used in electronic devices. They amplify the output voltage of signals.
5. Current Amps
They amplify the input current relative to the input current waveform.
Classification of Amplifiers
The classification of amplifiers depends on the signal size (large or small), how it processes the input signal, and its physical configuration. The different classes of amplifiers rely on the mode of operation. They include:
1. Class A
The collector current flow occurs for the entire AC signal circuit used. It has a high efficiency, power out/power in (Pout-Pin), expressed in 50% or more. However, it’s wasteful, and its actual electrical energy requirement dissipates even when the output is zero.
2. Class B
The collector current flow occurs for only half the cycle of input. As a result, it has low efficiency, power out/power in (Pout-Pin), expressed in 50%, and its modulation peaks at 100%. The main problem is that each transistor conducts for less than half a cycle. Distortion occurs on each signal waveform cycle as it passes through zero volts.
3. Class AB
It’s a combination of Classes A and B. Its primary advantage is that it overcomes the limitations of Classes A and B amplifiers. In addition, it’s more efficient than a Class B amplifier. So, it’s used in TV receivers, CD players, public address systems, satellite, and wireless communication systems.
4. Class C
The collector current flow occurs for less than half of the input cycle. As a result, the amplifier has a very low efficiency, power out/power in (Pout-Pin), expressed in 30% or less. Therefore, its use is limited to RF applications at 500 MHz to GHz frequencies because of the minimal output requirement.
5. Class D
It uses the PWM technique, generating large amounts of harmonics and making it possible to use smaller capacitors and inductors. As a result, it also has a higher efficiency and a better Signal-to-Noise Ratio (SNR) of 100dB.
Designing Amplifiers
Amplifier designers can use bipolar transistors, thermionic valves, vacuum tubes, or field effect transistors. Amplifiers are included in circuit blocks or integrated circuits to increase the signal quality level.
Amplifiers have two input and output terminals and a ground connection. They also have three properties:
- Input Resistance (RIN): It’s the resistance applied to the amplifier input and becomes a load to the source. Experts determine the resistance by measuring the input voltage and current and then using Ohm’s law.
- Output Resistance (ROUT): It’s the resistance within the amplifier and forms a potential divider network with the load applied to the amplifier.
- Gain or Amplification (A): The amplifier gain is a critical element of its performance.
An amplifier’s frequency response is the phase shift or changes in gain over a specified input signal frequency range. An increase in frequency makes the capacitive reactance smaller and decreases the signal voltage at the base and the amplifier’s voltage gain.
Amplifier design must also account for distortion, which implies the waveform variation received at the output relative to the applied input. The unwanted alterations generated are known as distortion. The types of distortions include:
- Frequency distortion where the amplifier has insufficient linear gain
- Harmonic distortion, where the amplifier generates overtones because of non-linearities in gain stages
- Hum caused by a poor power supply
- Noise
It’s crucial to ensure proper amplifier design and implementation to ensure they work correctly. The amp should use signal power with maximum efficiency and achieve a high signal-to-noise ratio. It should also provide excellent sound and signal quality with maximal clarity and minimal distortion.
Application of Amplifiers
Amplifiers used in electronic devices can increase the current, power, voltage, or signal. Therefore, they are crucial tools in broadcasting, wireless communication, audio systems, and medical equipment.
Amplifiers amplify signal quality, help in noise reduction, and minimize interference. Interference reduction also prevents any connected or adjacent nodes linked by radio signals from receiving or transmitting signals that conflict or blend together.
Choosing the Right Amplifier
The essential characteristics of all amplifiers are the gain and fidelity of their output relative to the input. Therefore, when selecting an amplifier, you need to consider the gain and fidelity, which have an inverse relationship.
Amplifiers generally have a power gain greater than one. On the other hand, fidelity has several properties, including the following:
- Bandwidth (a span of the useful frequency range)
- Linearity (comparison of the proportion of input and output)
- Noise (a measure of undesired signals)
- Slew rate (maximum rate of output change)
- Frequency response
- Rise and settling time
- Ringing and overshoot
- Stability and freedom from oscillation
When selecting the right amplifier, you must consider all the above fidelity properties, gain, power output, and distortion. A high-quality amplifier helps other audio system components work effectively and ensures the production of maximum sound quality.
The Right Amplifier Makes All the Difference
Amplifiers increase the amplitude of signal waveforms without changing other parameters like wave shape or frequency. As a result, they are critical electronic circuits and perform various functions in numerous systems. For example, they are widely used in broadcasting, wireless communication, audio systems, and medical equipment.
