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lp2bs(b, a, wo=1.0, bw=1.0)

Return an analog band-stop filter with center frequency :None:None:`wo` and bandwidth :None:None:`bw` from an analog low-pass filter prototype with unity cutoff frequency, in transfer function ('ba') representation.

Notes

This is derived from the s-plane substitution

$$s \rightarrow \frac{s \cdot \mathrm{BW}}{s^2 + {\omega_0}^2}$$

This is the "wideband" transformation, producing a stopband with geometric (log frequency) symmetry about :None:None:`wo`.

Parameters

b : array_like: Numerator polynomial coefficients.
a : array_like: Denominator polynomial coefficients.
wo : float: Desired stopband center, as angular frequency (e.g., rad/s). Defaults to no change.
bw : float: Desired stopband width, as angular frequency (e.g., rad/s). Defaults to 1.

Returns

b : array_like: Numerator polynomial coefficients of the transformed band-stop filter.
a : array_like: Denominator polynomial coefficients of the transformed band-stop filter.

Transform a lowpass filter prototype to a bandstop filter.

Examples

>>> from scipy import signal
... import matplotlib.pyplot as plt

>>> lp = signal.lti([1.0], [1.0, 1.5])
... bs = signal.lti(*signal.lp2bs(lp.num, lp.den))
... w, mag_lp, p_lp = lp.bode()
... w, mag_bs, p_bs = bs.bode(w)
... plt.plot(w, mag_lp, label='Lowpass')
... plt.plot(w, mag_bs, label='Bandstop')
... plt.semilogx()
... plt.grid()
... plt.xlabel('Frequency [rad/s]')
... plt.ylabel('Magnitude [dB]')
... plt.legend()

See :

Back References

The following pages refer to to this document either explicitly or contain code examples using this.

scipy.signal._filter_design.lp2hp scipy.signal._filter_design.lp2lp scipy.signal._filter_design.lp2bs scipy.signal._filter_design.lp2bs_zpk scipy.signal._filter_design.lp2bp scipy.signal._filter_design.bilinear

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