Interference at Odd vs Even Harmonics: Is the Square Wave Really Square?

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SUMMARY

The discussion centers on the harmonic structure of square wave signals, specifically addressing the unexpected interference at even harmonics instead of the anticipated odd harmonics. It is established that the ideal square wave, characterized by a 50% duty cycle, typically exhibits odd harmonics. However, real-world deviations, such as variations in pulse width and rise/fall times, can lead to the presence of even harmonics. This insight emphasizes the importance of understanding pulse signal characteristics in practical applications.

PREREQUISITES
  • Fourier Transform principles
  • Pulse width modulation techniques
  • Signal duty cycle analysis
  • Harmonic distortion in waveforms
NEXT STEPS
  • Study the effects of pulse width on harmonic content in square waves
  • Explore the relationship between rise/fall times and harmonic generation
  • Investigate practical applications of Fourier analysis in signal processing
  • Learn about filtering techniques to mitigate unwanted harmonics
USEFUL FOR

Electrical engineers, signal processing specialists, and anyone involved in waveform analysis and design will benefit from this discussion.

cyclone24
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If I look at the Fourier transform of the square wave signal, the peaks are at the odd multiples. In the device that I am working on, I would expect the interference at the odd harmonics of the center frequency.

But I see the interference at even harmonics. When is this possible?

(Only if the square wave is not really square?)
 
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cyclone24 said:
(Only if the square wave is not really square?)

Nothing is ideal in the real world.
 
The harmonic structure of a pulse signal depends on the duty-cycle. A real 50% square wave has the odd-harmonic structure you mention. Varying the pulse-width will produce different harmonics.
 
It turns out that the difference in rise and fall times lead to different harmonics (odd/even)...
 

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