Understanding Distortion in RF Amplifiers

This article explains the basics of distortion, its causes, and different types of distortion in RF amplifiers.

The definition of distortion is as follows: Distortion is basically an alteration in some of the parameters of a waveform or signal.

In the context of RF amplifiers, distortion refers to a change in the input waveform during the amplification process. This change is reflected in the output signal waveform when compared to the input waveform fed into the RF amplifier.

Causes of Distortion

Several factors can contribute to distortion in RF amplifiers:

• Weak Transistors/Tubes: Aging or damaged active components can introduce non-linearities.
• Overloaded Circuits: Exceeding the amplifier’s designed input power or output load can cause clipping and distortion.
• Defective Resistors: Resistors that have drifted out of tolerance or are failing can affect biasing and signal levels, leading to distortion.
• Leaky Coupling or Leaky Capacitors: Unwanted signal coupling or capacitor leakage can introduce noise and alter the signal waveform.
• Improper Matching of Electronic Components on PCB: Mismatched impedance or poorly optimized component values on the printed circuit board can cause signal reflections and distortion.

Types of Distortion

Here are some common types of distortion observed in RF amplifiers:

• Amplitude or Nonlinear Distortion: This occurs when the amplitude of the output signal is not a linear representation of the input signal.
• Frequency Distortion: This type of distortion arises when different frequency components of the input signal are amplified by different amounts.
• Phase Distortion: Phase distortion happens when different frequency components of the input signal experience different phase shifts as they pass through the amplifier.
• Crossover Distortion: This is a specific type of distortion that occurs in Class B amplifiers (and sometimes Class AB) near the crossover point where one transistor turns off and the other turns on. It creates a “notch” in the signal.
• Nonlinear Distortion: (Redundant, likely meant to be a separate type or a broader category encompassing amplitude distortion)
• Frequency Distortion: (Duplicated)
• Phase Shift Distortion: (Similar to Phase Distortion)

Refer to resources on different amplifier classes such as Class A, Class B, Class-AB, and Class C for more information on how amplifier design can affect distortion characteristics.