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# Fourier series output voltage RLC series bandpass filter in TINA-TI Spice

Other Parts Discussed in Thread: TINA-TI

Hello,

I try to simulate a RLC series bandpass filter in TINA-TI Spice. The component values are: R = 50 Ω, L = 99.5 uH, and C = 255 pF. The output voltage is measured across the resistor of 50 Ohm. I apply a sqaure wave voltage to this RLC series bandpass filter with an amplitude of 16 V, no DC component, and frequency of 1 MHz.

I would like to determine the Fourier coefficient of the input and output. The simulation produces correct Fourier coefficients for the input square wave voltage. However, the Fourier coefficients of the output voltage are not correct (they are smaller in amplitude and the corresponding phase is also not correct).

First, I ran transient response and make sure that the output is settled down. I simulate after 10 usec in order to get rid of the transient effects of the output voltage. Still, I get the wrong result.

From the Fourier series, we have only odd terms in the Fourier series for the square wave voltage.

FOR INPUT VOLTAGE:
n   Amplitude
1   20.37 V
3   6.79 V
5   4.07 V
7   2.91 V
9   2.26 V

FOR OUTPUT:
n   Amplitude
1   17.23 V (but I expected to have 20.37 V, since the RLC filter is tuned at 1 MHz (n =1))
3   229.96 mV
5   96.52 mV
7   50.76 mV
9   20.18 mV

Further information about the RLC circuit:
> Center frequency (resonant frequency) is 1 MHz
> Bandwidth is 80 kHz
> Gain at the center frequency is 1 (0 dB)

I attached the .TSC file, transient response, frequency response, and the Fourier coefficient for the input and output voltage.

• Hi Mehmet,

Since TINA is a DesignSoft/TINA program, questions are handled by using the DesignSoft support page: http://www.tina.com/technical-support/  .

The DesignSoft/TINA team is very helpful and this is the most direct way for TINA support.  Please advise by Reply when the issue has been resolved.

Regards,

~Leonard