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RF Modulation Types

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • RF modulation types can be categorized into digital modulation and analog modulation techniques.

  • Continuous wave modulation, such as AM, FM, and PM, alters the characteristics of a continuous carrier wave. In contrast, pulse modulation, such as PAM, PWM, and PPM, discretizes the analog signal into pulses.

  • Learn about digital modulation techniques, including ASK, FSK, PSK, and QAM.

Amplitude modulated and Frequency modulated sine waves

Amplitude modulation and Frequency modulation visualization

RF modulation types encompass a wide range of techniques utilized in radio frequency communication systems to transmit information over the airwaves. These modulation types can be broadly categorized into two main categories: digital modulation and analog modulation. Digital modulation techniques involve encoding digital data onto a carrier wave, while analog modulation techniques modify continuous waveforms to convey analog information.  

We’ll be delving into the intricacies of each below.

RF Modulation types

Continuous wave modulation methods, such as amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM), alter the characteristics of a continuous carrier wave. 

Conversely, pulse modulation techniques, including pulse amplitude modulation (PAM), pulse width modulation (PWM), and pulse position modulation (PPM), discretize the analog signal into pulses for transmission. 

Understanding the various RF modulation types is essential for comprehending the principles underlying wireless communication systems and the diverse mechanisms involved in transmitting digital and analog signals over the radio frequency spectrum.

RF Modulation Types

Analog Modulation (Analog data)

Digital Modulation (Digital data)

Continuous Wave Modulation (Analog carrier)

Pulse Modulation (Digital Carrier)
  • Amplitude Shift Keying (ASK)
  • Frequency Shift Keying (FSK)
  • Phase Shift Keying (PSK)
  • Quadrature amplitude modulation (QAM)
  • Amplitude Modulation (AM)
  • Frequency Modulation (FM)
  • Phase modulation (PM)
  • Pulse Amplitude Modulation (PAM)
  • Pulse Width Modulation (PWM)
  • Pulse Code Modulation (PCM)

Analog modulation is a fundamental concept in communication systems, encompassing continuous wave and pulse modulation techniques. Both techniques feature an analog wave as the modulating signal. In continuous wave modulation, the carrier wave is also an analog signal, whereas, in pulse modulation, the carrier signal is a series of varying pulses.

Continuous Wave Modulation

This modulation method forms the basis for several widely used modulation techniques.  The characteristics of carrier waves (amplitude, frequency, and phase) are manipulated in response to the modulation signal. The most commonly used analog continuous wave modulation types are Amplitude Modulation (AM), Frequency Modulation (FM), and Phase Modulation (PM)

  • Amplitude Modulation (AM) is where the amplitude of the carrier wave is varied in proportion to the instantaneous amplitude of the modulated signal.

  • Frequency Modulation (FM) is where the frequency of the carrier waves varies in accordance with the input-modulating signal. The resulting waveform has a constant amplitude, with a slight deviation in frequency from the carrier signal.  FM has better noise interference compared to AM.

  • Phase Modulation (PM) has the instantaneous phase of the carrier wave directly proportional to the amplitude of the modulating signal. As the modulating signal varies, it causes the phase of the wave to change accordingly. 

Pulse Modulation

Analog pulse modulation is a technique used to transmit analog signals by discretizing them into a series of pulses. This allows for efficient and accurate transmission of continuous signals. Popular analog pulse modulation techniques include Pulse Amplitude Modulation (PAM), Pulse Width Modulation (PWM), Pulse Position Modulation (PPM), and Pulse Code Modulation (PCM).

  • Pulse Amplitude Modulation (PAM) modifies the amplitude of a series of pulses in accordance with the instantaneous amplitude of the analog signal. The amplitude of each pulse represents the corresponding amplitude of the original signal. 

  • In Pulse Width Modulation (PWM) schemes, the width of the pulses is varied in accordance with the instantaneous amplitude of the analog signal. 

  • Pulse Position Modulation (PPM) is a modulation technique where the position of a series of pulses within a fixed time period is varied in response to the instantaneous amplitude of the analog signal.

  • Pulse Code Modulation (PCM) is an analog modulation technique that involves sampling the analog signal at regular intervals, quantizing the sampled values, and encoding them as binary numbers. 

Digital Modulation

In digital modulation techniques, the carrier wave is digital and, in most RF modulation cases, is superimposed on an analog carrier.

  • In Amplitude Shift Keying (ASK), different amplitude levels are assigned to different binary values. The carrier wave’s instantaneous amplitude is modified based on the digital signal’s value.

  • In Frequency Shift Keying (FSK), the carrier frequency is switched between two predetermined frequencies, one representing a binary 0 and the other representing a binary 1. 

  • In Phase Shift Keying (PSK), the phase of the carrier wave is adjusted at specific intervals based on the digital signal being transmitted

  • Quadrature Amplitude Modulation (QAM) is a method that involves two message signals. The amplitudes of two carrier waves are modulated (often using ASK). These two carrier waves are out of phase with each other by 90 degrees. The waves are then added together to create a single signal. Once broadcasted and received, these two signals are demodulated and then separated. QAM’s higher data rate capabilities and robustness to noise and interference make it a preferred choice for various digital communication systems. 

Further, there are a variety of other digital modulation techniques commonly used in modern electronics that rely on combining shift keying methods. 

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