isstable
Verify that discrete-time filter System object is stable
Description
Examples
Determine if Filter Has Minimum Phase and is Stable
Design a Chebyshev Type I IIR filter and determine if the filter has minimum phase and is stable.
Using the fdesign.lowpass
and design
functions, design a Chebyshev Type I IIR filter with a passband ripple of 0.5 dB and a 3 dB cutoff frequency at 9600 Hz.
Fs = 48000; % Sampling frequency of input signal d = fdesign.lowpass('N,F3dB,Ap', 10, 9600, .5, Fs); filt = design(d,'cheby1',Systemobject=true)
filt = dsp.SOSFilter with properties: Structure: 'Direct form II' CoefficientSource: 'Property' Numerator: [5x3 double] Denominator: [5x3 double] HasScaleValues: true ScaleValues: [0.3318 0.2750 0.1876 0.0904 0.0225 0.9441] Use get to show all properties
Using the isminphase
function, determine if the filter has minimum phase.
isminphase(filt)
ans = logical
1
Verify the location of poles and zeros of the filter transfer function on the z-plane. By definition, the poles and zeros of the minimum phase filter must be on or inside the unit circle.
zplane(filt)
All minimum phase filters are stable. To verify if the designed filter is stable, use the isstable
function.
isstable(filt)
ans = logical
1
Input Arguments
sysobj
— Filter System object
filter System object
arithType
— Arithmetic type
'double'
(default) | 'single'
| 'Fixed'
Arithmetic used in the filter analysis, specified as 'double'
,
'single'
, or 'Fixed'
. When the arithmetic
input is not specified and the filter System object is unlocked, the analysis tool assumes a double-precision filter. When the
arithmetic input is not specified and the System object is locked, the function performs the analysis based on the data type of
the locked input.
The 'Fixed'
value applies to filter System objects with fixed-point
properties only.
When the 'Arithmetic'
input argument is specified as
'Fixed'
and the filter object has the data type of the
coefficients set to 'Same word length as input'
, the arithmetic
analysis depends on whether the System object is unlocked or locked.
unlocked –– The analysis object function cannot determine the coefficients data type. The function assumes that the coefficients data type is signed, has a 16-bit word length, and is auto scaled. The function performs fixed-point analysis based on this assumption.
locked –– When the input data type is
'double'
or'single'
, the analysis object function cannot determine the coefficients data type. The function assumes that the data type of the coefficients is signed, has a 16-bit word length, and is auto scaled. The function performs fixed-point analysis based on this assumption.
To check if the System object is locked or unlocked, use the isLocked
function.
When the arithmetic input is specified as 'Fixed'
and the filter
object has the data type of the coefficients set to a custom numeric type, the object
function performs fixed-point analysis based on the custom numeric data type.
Output Arguments
flag
— Flag to determine if filter is stable
1
| 0
Flag to determine if the filter is stable, returned as a logical:
1
–– Filter is stable.0
–– Filter is not stable.
Data Types: logical
Version History
Introduced in R2013aR2024b: Support for dsp.VariableFIRDecimator
and dsp.VariableFIRInterpolator
Objects
Starting in R2024b, the isstable
analysis function supports the
dsp.VariableFIRDecimator
and dsp.VariableFIRInterpolator
objects.
R2024b: dsp.BiquadFilter
object warns
The dsp.BiquadFilter
object issues a warning and will be removed in a
future release. Use the dsp.SOSFilter
object
instead. For more information on how to replace your existing code, see the
Compatibility Considerations section in the dsp.BiquadFilter
reference page.
R2024b: Support for dsp.DCBlocker
object
Starting in R2024b, this function supports the dsp.DCBlocker
object.
R2023b: Support for dsp.ParallelFilter
and dsp.Delay
Objects
Starting in R2023b, the isstable
analysis function supports the
dsp.ParallelFilter
and the dsp.Delay
objects.
R2023b: dsp.BiquadFilter
object will be removed
The dsp.BiquadFilter
object will be removed in a future release. Use
the dsp.SOSFilter
object
instead.
See Also
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