Fourer Analyzer University of Florida傅里叶分析仪佛罗里达大学.pptVIP

Fourier Analyzer LC Resonant Circuit There is certain resonant frequency in which both capacitor and inductor like to react. LC Resonant Circuit If the input matches with such frequency, then both will oscillate in harmony. But if the input frequency is different than resonant frequency, then the LC parallel portion will resist against it (or attenuate the inputs). For this circuit, such resonant frequency f0 was found as 16kHz. Now the circuit is driven with square wave of f0 =16kHz and 1.2V amplitude. Output for 16kHz 1.2V input Vout = 1.2V, Periods of input and output are same, which means it’s the first peak response The Second Peak Response The Third Peak Response SUMMARY CONCLUSION * * Vout = 0.42V, The input frequency was 5.3kHz Vout = 0.25V, Input frequency was 3.2kHz Third Res. Second Res. First Response 0.25 V 3.2kHz 0.42 V 5.3kHz 1.2 V 16kHz Output V Input frequency But! 5.3kHz ≈ (1/3) x 16kHz, 3.2kHz ≈ (1/5) x 16kHz. And also 0.42V ≈ (1/3) x 1.2V, 0.25V ≈ (1/5) x 1.2V Those are just coefficient of Fourier Series of square function. Our detector frequency (16kHz) is fixed. The square wave frequency changes. We get one or another of several frequency components of the square wave. * * *