What is SFDR?

What is Spurious-Free Dynamic Range?

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- everything RF

Aug 26, 2023

The Spurious-Free Dynamic Range (SFDR) of a receiver is a ratio of the amplitude of the fundamental carrier signal to the amplitude of the strongest spurious signal in the frequency range of interest. SFDR is usually measured in dBc (i.e. with respect to the carrier signal amplitude). 

SFDR is a measure of the purity of a signal in the presence of unwanted spurious signals or distortions. It is an important specification used to assess the quality of analog and digital systems that process signals. SFDR is basically the effective dynamic range of a system while taking into account the presence of spurious components such as harmonics, intermodulation products, and noise. Essentially, it tells us how much stronger the main signal is compared to the undesired spurious components.

Mathematically, it is the dynamic ratio between the root mean square (rms) value of the power of a carrier and the rms value of the next most significant spurious signal seen in the frequency domain.

SFDR is often quantified as the range, in units of power (dBc), with respect to the carrier signal frequency. However, it also could be referenced to a full-scale signal in units of power (dBFS).

In case the next spurious signal falls outside the frequency range of interest, then SFDR can not be calculated. Factors that dominate the SFDR include Noise figure, 2nd and 3rd Order Intercept, 1-dB Compression, Internal Spurs and Bandwidth.

Where does SFDR come in to play?

SFDR is a critical parameter in various applications where signal quality is paramount. Here are some areas where SFDR plays a significant role: 

  • Communications Systems: In wireless communication, RF (Radio Frequency) front-end components must maintain a high SFDR to minimize interference and distortion in transmitted signals. 
  • Analog-to-Digital Converters (ADCs): In ADCs, SFDR is crucial to ensure that the digitized output accurately represents the input signal, without introducing unwanted artifacts. 
  • Audio Systems: High-fidelity audio systems require low distortion and high SFDR to reproduce music and sound accurately. 
  • Radar and Sonar Systems: SFDR is vital for radar and sonar systems to distinguish between weak and strong echoes, enabling precise target detection. 
  • Test and Measurement Equipment: Instruments such as oscilloscopes and spectrum analyzers rely on SFDR to provide accurate measurements of signals, even in the presence of interference. 

How can you improve SFDR?

The following techniques can be used to enhance SFDR in systems: 

Filtering: Employing high-quality filters to suppress unwanted spurious components, such as harmonic filters in RF circuits. 

Nonlinear Distortion Reduction: Designing circuits and systems to minimize nonlinear distortion, often through careful component selection and circuit design. 

Digital Signal Processing (DSP): In digital systems, DSP algorithms can be used to reduce spurious components. 

Noise Reduction: Reducing noise sources and employing noise-reduction techniques can improve SFDR. 

Spurious Free Dynamic Range (SFDR) is a critical parameter that defines the purity of signals in various applications. Achieving a high SFDR is essential in communication systems, measurement equipment, audio systems, and more, as it ensures that the desired signal remains free from distortion and interference. Engineers and scientists continue to push the boundaries of technology to improve SFDR, enabling us to enjoy cleaner and more reliable signals in our modern, interconnected world.