How to Amplify Audio Signals

 Key Takeaways

  • Input to audio amplifiers is in the frequency range of 30Hz to 15kHz.

  • Audio amplifiers are widely used in sound systems, musical instruments, radio broadcasting systems, wireless transmitters, and long-distance signal transmission systems.

  • Class D amplifiers employ pulse width modulation (PWM) to produce output voltage pulses that approximate the analog input signal. 

Audio amplifiers

The class D power amplifier is the most popular audio signal amplifier due to its light weight and heat dissipation characteristics

Learning how to amplify audio signals is critical when designing systems with microphones, wireless transmitters, or radio devices. Audio signals are large signals, and power amplifiers are used to enhance these audio signals. The class D power amplifier is the most popular audio signal amplifier due to its light weight and heat dissipation characteristics. It offers the lowest distortion in audio signals. In this article, we will discuss how audio signal amplification works as well as the specifics of class D amplifiers.

Why Is Amplifying Audio Signals Important?

There are several cases where an audio signal must be amplified. Let’s use an example of a public address system. When a speaker delivers his or her voice into a microphone, the sound signal gets converted into electrical signals. The electrical signals are of low voltage, in the range of millivolts. Low voltage signals are incapable of driving the loudspeaker to give audio output. The low voltage signals need to be amplified to sufficient high voltage levels. For audio signal amplification, audio amplifiers can be utilized. Amplifiers are electronic circuits that output the input signal with a gain. They amplify the signal with minimum distortion. Amplifiers can be classified according to their modes of operation, circuit configuration, and coupling. 

Amplifier Classification 

Based on the frequency of operation, amplifiers are classified as:

  1. DC amplifiers - Amplify signals from zero frequency to about 10 Hz.

  2. Audio amplifiers - The input to the audio amplifiers is in the frequency range of 30Hz to about 15kHz.

  3. Wide-band amplifiers or video amplifiers - Video amplifiers work on the input signals of frequencies up to a few MHz.

  4. RF amplifiers - The input signals to RF amplifiers are in the range of a few kHz to hundreds of MHz. 

How to Amplify Audio Signals Using Audio Amplifiers  

Audio amplifiers are employed for the amplification of sound signals. Audio amplifiers belong to large signal amplifiers. They are power amplifiers that require high switching signals. Most of the audio amplifiers in applications are multi-stage amplifiers.

Audio amplifiers consist of active semiconductor devices such as bipolar junction transistors (BJT) or field-effect transistors (FET). The configuration of audio amplifiers and the transistor connection depends on factors such as noise, frequency of operation, distortion, and gain requirements.

When the electrical signals from a microphone reach a transistor, it initiates movements of majority and minority charge carriers. According to the amplification required, more transistors are included in the amplifier circuit, which adds to the stages. With the charge carrier movements, the signal reaches the last stage of the multi-stage amplifier. The signal at the output end is a replica of the input signal with gain. 

Class D Audio Amplifiers

Audio amplifiers are widely used in sound systems, musical instruments, radio broadcasting systems, wireless transmitters, and long-distance signal transmission systems. There are different classifications of audio amplifiers, such as Class A, B, AB, D. G, DG, and H. The most widely-used class of audio amplifiers is class D amplifiers.

Class D amplifiers are different from class A, B, and AB amplifiers, as they do not draw large power in the output stage. Some advantages of Class D amplifiers include:

  • Low power dissipation

  • Less heat production

  • Less thermal management required

  • Less board space consumed

  • Extended battery life

  • Lower cost

In class D amplifiers, output voltage pulses switch between positive and negative power supplies. These amplifiers employ pulse width modulation (PWM) to produce the output voltage pulses that approximate the analog input signal. When not switching, the transistors in the output stages are fully turned off. In this state, these transistors draw no current, reducing the power dissipation significantly. The power loss is reduced, as the transistors are either fully turned on or fully turned off. The transistors operate in the switching region rather than the active region as in other audio amplifiers. The reduction in the power loss in class D amplifiers improves efficiency, typically around 90%.

The solution for how to amplify audio signals in portable audio devices lies in the use of class D amplifiers. These amplifiers are affordable, highly reliable, and showcase excellent performance in car and home audio amplifiers. They offer low pop noise and noise reduction with differential inputs.

To design reliable, efficient audio amplifier circuits, Cadence’s PCB design and analysis software can be utilized. Leading electronics providers rely on Cadence products to optimize power, space, and energy needs for a wide variety of market applications. If you’re looking to learn more about our innovative solutions, talk to our team of experts or subscribe to our YouTube channel.

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