pydsm.delsig.synthesizeChebyshevNTF

pydsm.delsig.synthesizeChebyshevNTF(order=3, osr=64, opt=0, H_inf=1.5, f0=0.0)

Synthesize the NTF for a DS modulator by a Chebyshev function.

This function is an alternative to synthesizeNTF which assumes that the magnitude of the denominator of the NTF is approximately constant in the passband. When the OSR or H_inf are low, this assumption breaks down and synthesizeNTF yields a non-optimal NTF. The synthesizeChebyshevNTF creates non-optimal NTFs, but fares better than synthesizeNTF in the aforementioned circumstances. The NTF is obtained from a type-2 highpass Chebyshev function.

Parameters

orderint, optional

the order of the modulator, defaults to 3

osrfloat, optional

the oversamping ratio (based on the actual signal bandwidth)

optint, optional

ignored, present for signature compatibility with synthesizeNTF

H_infreal, optional

max allowed peak value of the NTF. Defaults to 1.5

f0real, optional

center frequency, defaults to 0. 1 corresponds to the sampling frequency, so that 0.5 is the maximum value. Value 0 specifies an LP modulator.

Returns

ntftuple

noise transfer function in zpk form.

Raises

ValueError

‘Order must be even for a bandpass modulator.’ if the order is incompatible with the modulator type.

Notes

Parameter opt is ignored.