Types of Class D Amplifiers: A Complete Visual Guide

 

Types of Class D Amplifiers: A Complete Visual Guide

Class D amplifiers have become the backbone of modern audio systems due to their high efficiency, compact size, and powerful output. They are widely used in home audio, car audio, portable speakers, and professional sound systems.

This guide explains the different types of Class D amplifiers with clear visuals to make the concepts easy to understand.

What Is a Class D Amplifier?


Alt text: Class D amplifier block diagram showing PWM modulator, switching stage, and LC filter

A Class D amplifier is a switching amplifier that converts the input audio signal into high-frequency pulses. These pulses drive power transistors that switch fully ON and OFF, resulting in efficiency levels up to 95%.

Unlike Class A or Class AB amplifiers, Class D amplifiers waste very little energy as heat.

Types of Class D Amplifiers

Class D amplifiers are classified based on:

  • Modulation technique

  • Output topology

  • Feedback method

  • Input signal type

Let’s explore each type with diagrams.

1. Types of Class D Amplifiers Based on Modulation Method

1.1 PWM (Pulse Width Modulation) Class D Amplifier


Alt text: PWM waveform showing pulse width variation with audio signal

In PWM Class D amplifiers, the width of the pulses changes according to the audio signal.

Key Features:

  • Most widely used

  • Simple and cost-effective

  • Good balance of efficiency and sound quality

Applications:
Home audio systems, consumer electronics

1.2 PDM (Pulse Density Modulation) Class D Amplifier


Alt text: Pulse density modulation waveform with varying pulse density

Here, the number of pulses per unit time represents the audio signal instead of pulse width.

Key Features:

  • Better noise shaping

  • Common in digital signal processing

  • Similar to delta-sigma modulation

1.3 Delta-Sigma (ΣΔ) Class D Amplifier


Alt text: Delta-sigma modulation block diagram used in Class D amplifiers

Delta-Sigma Class D amplifiers use oversampling and noise shaping to push distortion outside the audible range.

Key Features:

  • Very low distortion

  • Excellent audio clarity

  • Used in high-end audio systems

1.4 Self-Oscillating Class D Amplifier


Alt text: Self-oscillating Class D amplifier feedback loop diagram

This type generates its own switching frequency using feedback.

Key Features:

  • No external clock

  • Automatically adapts to speaker load

  • Preferred by audiophiles

2. Types of Class D Amplifiers Based on Output Topology

2.1 Half-Bridge Class D Amplifier


Alt text: Half bridge Class D amplifier circuit diagram

Advantages:

  • Simple design

  • Low component count

Disadvantages:

  • Requires output capacitor or dual supply

Applications:
Low-power speakers, portable devices

2.2 Full-Bridge (H-Bridge) Class D Amplifier


Alt text: Full bridge H-bridge Class D amplifier schematic

Advantages:

  • Higher output power

  • No output coupling capacitor

  • Better speaker control

Applications:
Car audio systems, subwoofers, PA systems

3. Types of Class D Amplifiers Based on Feedback Method


Alt text: Comparison of pre-filter and post-filter feedback in Class D amplifiers

Open-Loop Class D Amplifier

  • No feedback

  • Simple but higher distortion

Closed-Loop Class D Amplifier

  • Uses negative feedback

  • Improved frequency response

Pre-Filter Feedback

  • Easier to design

  • Load-dependent behavior

Post-Filter Feedback

  • Feedback taken after LC filter

  • Best audio fidelity

  • Load-independent performance

4. Types of Class D Amplifiers Based on Input Signal


Alt text: Analog input vs digital input Class D amplifier comparison

Analog Input Class D Amplifier

  • Accepts analog audio

  • Converts to PWM internally

Digital Input Class D Amplifier

  • Accepts digital audio (I²S, SPDIF)

  • No DAC required

  • Often called digital power amplifiers

Advantages of Class D Amplifiers


Alt text: Advantages of Class D amplifiers including efficiency and compact size

  • Very high efficiency

  • Lightweight and compact

  • Minimal heat generation

  • Ideal for battery-powered devices

Conclusion

Class D amplifiers come in many forms, each optimized for specific applications. Whether you need maximum efficiency, high audio fidelity, or compact size, there is a Class D amplifier type suited for your needs.

With ongoing advancements in modulation and feedback techniques, Class D amplifiers continue to dominate the future of audio amplification.

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