Differentiator filter specification object
D = fdesign.differentiator
D = fdesign.differentiator(SPEC)
D = fdesign.differentiator(SPEC,specvalue1,specvalue2, ...)
D = fdesign.differentiator(specvalue1)
D = fdesign.differentiator(...,Fs)
D = fdesign.differentiator(...,MAGUNITS)
D = fdesign.differentiator constructs
a default differentiator filter designer
the filter order set to 31.
D = fdesign.differentiator(SPEC) initializes
the filter designer
Specification property to
You provide one of the following filter entries as input to replace
These entries are not case sensitive.
Specifications marked with an asterisk require the DSP System Toolbox™ software.
'N'— Full band differentiator (default)
'N,Fp,Fst'— Partial band differentiator
'N,Fp,Fst,Ap'— Partial band differentiator *
'N,Fp,Fst,Ast'— Partial band differentiator *
'Ap'— Minimum order full band differentiator *
'Fp,Fst,Ap,Ast'— Minimum order partial band differentiator *
The filter specifications are defined as follows:
Ap— amount of ripple allowed in the pass band in decibels (the default units). Also called Apass.
Ast— attenuation in the stop band in decibels (the default units). Also called Astop.
Fp— frequency at the start of the pass band. Specified in normalized frequency units. Also called Fpass.
Fst— frequency at the end of the stop band. Specified in normalized frequency units. Also called Fstop.
N— filter order.
that all frequency specifications are provided in normalized frequency
units. Also, decibels is the default for all magnitude specifications.
designopts to determine
the design options for a given design method. Enter
the MATLAB® command line to obtain detailed help on the design
options for a given design method,
D = fdesign.differentiator(SPEC,specvalue1,specvalue2,
...) initializes the filter designer specifications in
and so on. To get a description of the specifications
and more, enter
at the Command prompt.
D = fdesign.differentiator(specvalue1) assumes
the default specification
N, setting the filter
order to the value you provide.
D = fdesign.differentiator(...,Fs) adds
Fs, specified in Hz to define the
sampling frequency to use. In this case, all frequencies in the specifications
are in Hz as well.
D = fdesign.differentiator(...,MAGUNITS) specifies
the units for any magnitude specification you provide in the input
MAGUNITS can be one of
'linear'— specify the magnitude in linear units
'dB'— specify the magnitude in dB (decibels)
'squared'— specify the magnitude in power units
When you omit the
that all magnitudes are in decibels. Note that
all magnitude specifications in decibels (converting to decibels when
necessary) regardless of how you specify the magnitudes.
FIR Differentiator Filters
Design a 33rd-order FIR differentiator using least squares. Plot the zero-phase response of the filter.
d = fdesign.differentiator(33); hd = design(d,'firls','SystemObject',true); zerophase(hd)
Design a 54th-order narrowband equiripple differentiator. Differentiate the lowest 25% of the frequencies in the Nyquist range and filter the higher frequencies. Specify a sample rate of 20 kHz, a passband frequency of 2.5 kHz, and a stopband frequency of 3 kHz.
Fs = 20000; d = fdesign.differentiator('N,Fp,Fst',54,2500,3000,Fs); Hd = design(d,'equiripple','SystemObject',true);
Redesign the filter, but this time weight the stopband to increase the attenuation.
Hd1 = design(d,'equiripple','Wstop',4,'SystemObject',true); hfvt = fvtool(Hd,Hd1,'MagnitudeDisplay','zero-phase', ... 'FrequencyRange','[0, Fs/2)'); legend(hfvt,'No stopband weighting','Stopband weighting');