dsp.CICCompensationDecimator
Compensate for CIC decimation filter using FIR decimator
Description
You can compensate for the shortcomings of a CIC decimator, namely its passband droop and wide transition region, by following it with a compensation decimator. This System object™ lets you design and use such a filter.
To compensate for the shortcomings of a CIC filter using an FIR decimator:
Create the
dsp.CICCompensationDecimator
object and set its properties.Call the object with arguments, as if it were a function.
To learn more about how System objects work, see What Are System Objects?
Creation
Syntax
Description
returns a System object, ciccompdec
= dsp.CICCompensationDecimatorciccompdec
, that applies an FIR decimator to each
channel of an input signal. Using the properties of the object, the decimation filter can
be designed to compensate for a preceding CIC filter.
returns a CIC compensation decimator System object, with the ciccompdec
= dsp.CICCompensationDecimator(decim
)DecimationFactor
property set to
decim
.
returns a CIC compensation decimator System object, with the ciccompdec
= dsp.CICCompensationDecimator(cic
)CICRateChangeFactor
,
CICNumSections
, and CICDifferentialDelay
properties specified in the dsp.CICDecimator
System object, cic
.
returns a CIC compensation decimator System object, ciccompdec
= dsp.CICCompensationDecimator(cic
,decim
)ciccompdec
, with the
CICRateChangeFactor
, CICNumSections
, and
CICDifferentialDelay
properties specified in the
dsp.CICDecimator
System object
cic
, and the DecimationFactor
property set to
decim
.
returns a CIC compensation decimator object with properties specified by one or more
name-value pair arguments. Unspecified properties have default values.ciccompdec
= dsp.CICCompensationDecimator(___,Name=Value
)
Properties
Unless otherwise indicated, properties are nontunable, which means you cannot change their
values after calling the object. Objects lock when you call them, and the
release
function unlocks them.
If a property is tunable, you can change its value at any time.
For more information on changing property values, see System Design in MATLAB Using System Objects.
CICRateChangeFactor
— Rate-change factor of the CIC filter being compensated
2
(default) | positive integer scalar
Specify the rate-change factor of the CIC filter being compensated as a positive integer scalar.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
CICNumSections
— Number of sections of the CIC filter being compensated
2
(default) | positive integer scalar
Specify the number of sections of the CIC filter being compensated as a positive integer scalar.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
CICDifferentialDelay
— Differential delay of the CIC filter being compensated
1
(default) | positive integer scalar
Specify the differential delay of the CIC filter being compensated as a positive integer scalar.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
DecimationFactor
— Decimation factor of compensator
2
(default) | positive integer scalar
Specify the decimation factor of the compensator System object as a positive integer scalar.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
NormalizedFrequency
— Option to set frequencies in normalized units
false
(default) | true
Since R2024a
Option to set frequencies in normalized units, specified as one of these values:
true
–– The passband frequency Fpass and stopband frequency Fstop must be in the normalized frequency units and must be in the range Fpass < Fstop < 1.0.When you set the
NormalizedFrequency
property totrue
while creating the object and you do not set the passband and stopband frequencies, the object automatically sets the default values to normalized frequency units using the default sample rate of 1200 kHz.ciccompdec = dsp.CICCompensationDecimator(NormalizedFrequency=true)
ciccompdec = dsp.CICCompensationDecimator with properties: CICRateChangeFactor: 2 CICNumSections: 2 CICDifferentialDelay: 1 DecimationFactor: 2 NormalizedFrequency: true DesignForMinimumOrder: true PassbandFrequency: 0.1667 StopbandFrequency: 0.6667 PassbandRipple: 0.1000 StopbandAttenuation: 60
When you set the
NormalizedFrequency
property totrue
after you create the object, you must specify the passband and stopband frequencies in normalized units before you run the object algorithm.ciccompdec = dsp.CICCompensationDecimator
ciccompdec = dsp.CICCompensationDecimator with properties: CICRateChangeFactor: 2 CICNumSections: 2 CICDifferentialDelay: 1 DecimationFactor: 2 NormalizedFrequency: false DesignForMinimumOrder: true PassbandFrequency: 100000 StopbandFrequency: 400000 PassbandRipple: 0.1000 StopbandAttenuation: 60 SampleRate: 1200000
To specify the normalized frequency value, set
NormalizedFrequency
totrue
and manually convert the frequency value in Hz to the normalized value using the input sample rate in Hz. For example, if the input sample rate Fs is 1200 kHz, the corresponding passband frequency value in normalized units is FpassHz/(Fs/2) and the corresponding stopband frequency in normalized units is FstopHz/(Fs/2).ciccompdec = dsp.CICCompensationDecimator; ciccompdec.NormalizedFrequency = true; ciccompdec.PassbandFrequency = 100000/(1200000/2); ciccompdec.StopbandFrequency = 400000/(1200000/2)
ciccompdec = dsp.CICCompensationDecimator with properties: CICRateChangeFactor: 2 CICNumSections: 2 CICDifferentialDelay: 1 DecimationFactor: 2 NormalizedFrequency: true DesignForMinimumOrder: true PassbandFrequency: 0.1667 StopbandFrequency: 0.6667 PassbandRipple: 0.1000 StopbandAttenuation: 60
false
–– The passband and stopband frequency values are in Hz. You can specify the input sample rate through theSampleRate
property.
Data Types: logical
DesignForMinimumOrder
— Design filter of minimum order or of specified order
true
(default) | false
Specify whether to design a filter of minimum order or a filter of specified order
as a logical scalar. The default is true
, which corresponds to a
filter of minimum order.
FilterOrder
— Order of decimation compensator filter
12 (default) | positive integer scalar
Specify the order of the decimation compensator filter as a positive integer scalar.
Dependencies
To enable this property, set the DesignForMinimumOrder
property to false
.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
PassbandFrequency
— Passband edge frequency
100000
(default) | positive real scalar
Passband edge frequency Fpass, specified as a positive real scalar in Hz or in normalized frequency units (since R2024a).
If you set the
NormalizedFrequency
property to:
false
–– The value of the passband frequency is in Hz and must be in the range Fpass < Fstop < Fs/2, where Fstop is the stopband frequency and Fs is the input sample rate.true
–– The value of the passband frequency is in normalized frequency units and must be in the range Fpass < Fstop <1.0
.When you set the
NormalizedFrequency
property totrue
while creating the object and you do not set the passband frequency, the object automatically sets the default passband frequency to normalized frequency units using the default sample rate of 1200 kHz.ciccompdec = dsp.CICCompensationDecimator(NormalizedFrequency=true)
ciccompdec = dsp.CICCompensationDecimator with properties: CICRateChangeFactor: 2 CICNumSections: 2 CICDifferentialDelay: 1 DecimationFactor: 2 NormalizedFrequency: true DesignForMinimumOrder: true PassbandFrequency: 0.1667 StopbandFrequency: 0.6667 PassbandRipple: 0.1000 StopbandAttenuation: 60
When you set the
NormalizedFrequency
property totrue
after you create the object, you must specify the passband frequency in normalized units before you run the object algorithm.ciccompdec = dsp.CICCompensationDecimator
ciccompdec = dsp.CICCompensationDecimator with properties: CICRateChangeFactor: 2 CICNumSections: 2 CICDifferentialDelay: 1 DecimationFactor: 2 NormalizedFrequency: false DesignForMinimumOrder: true PassbandFrequency: 100000 StopbandFrequency: 400000 PassbandRipple: 0.1000 StopbandAttenuation: 60 SampleRate: 1200000
To specify the normalized frequency value, set
NormalizedFrequency
totrue
and manually convert the frequency value in Hz to the normalized value using half the input sample rate in Hz. For example, if the input sample rate Fs is 1200 kHz, the corresponding passband frequency value in normalized units is FpassHz/(Fs/2).ciccompdec.NormalizedFrequency = true; ciccompdec.PassbandFrequency = 100000/(1200000/2)
ciccompdec = dsp.CICCompensationDecimator with properties: CICRateChangeFactor: 2 CICNumSections: 2 CICDifferentialDelay: 1 DecimationFactor: 2 NormalizedFrequency: true DesignForMinimumOrder: true PassbandFrequency: 0.1667 StopbandFrequency: 400000 PassbandRipple: 0.1000 StopbandAttenuation: 60
(since R2024a)
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
StopbandFrequency
— Stopband edge frequency
400000
(default) | positive real scalar
Stopband edge frequency Fstop, specified as a positive real scalar in Hz or in normalized frequency units (since R2024a).
If you set the
NormalizedFrequency
property to:
false
–– The value of the stopband frequency is in Hz and must be in the range Fpass < Fstop < Fs/2, where Fpass is the passband frequency and Fs is the input sample rate.true
–– The value of the stopband frequency is in normalized frequency units and must be in the range Fpass < Fstop <1.0
.When you set the
NormalizedFrequency
property totrue
while creating the object and you do not set the stopband frequency, the object automatically sets the default stopband frequency to normalized frequency units using the default sample rate of 1200 kHz.ciccompdec = dsp.CICCompensationDecimator(NormalizedFrequency=true)
ciccompdec = dsp.CICCompensationDecimator with properties: CICRateChangeFactor: 2 CICNumSections: 2 CICDifferentialDelay: 1 DecimationFactor: 2 NormalizedFrequency: true DesignForMinimumOrder: true PassbandFrequency: 0.1667 StopbandFrequency: 0.6667 PassbandRipple: 0.1000 StopbandAttenuation: 60
When you set the
NormalizedFrequency
property totrue
after you create the object, you must specify the passband frequency in normalized units before you run the object algorithm.ciccompdec = dsp.CICCompensationDecimator
ciccompdec = dsp.CICCompensationDecimator with properties: CICRateChangeFactor: 2 CICNumSections: 2 CICDifferentialDelay: 1 DecimationFactor: 2 NormalizedFrequency: false DesignForMinimumOrder: true PassbandFrequency: 100000 StopbandFrequency: 400000 PassbandRipple: 0.1000 StopbandAttenuation: 60 SampleRate: 1200000
To specify the normalized frequency value, set
NormalizedFrequency
totrue
and manually convert the frequency value in Hz to the normalized value using half the input sample rate in Hz. For example, if the input sample rate Fs is 1200 kHz, the corresponding stopband frequency value in normalized units is FstopHz/(Fs/2).ciccompdec.NormalizedFrequency = true; ciccompdec.StopbandFrequency = 400000/(1200000/2)
ciccompdec = dsp.CICCompensationDecimator with properties: CICRateChangeFactor: 2 CICNumSections: 2 CICDifferentialDelay: 1 DecimationFactor: 2 NormalizedFrequency: true DesignForMinimumOrder: true PassbandFrequency: 100000 StopbandFrequency: 0.6667 PassbandRipple: 0.1000 StopbandAttenuation: 60
(since R2024a)
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
PassbandRipple
— Filter passband ripple in decibels
0.1
(default) | positive real scalar
Specify the filter passband ripple as a positive real scalar expressed in decibels.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
StopbandAttenuation
— Filter stopband attenuation in decibels
60
(default) | positive real scalar
Specify the filter stopband attenuation as a positive real scalar expressed in decibels.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
SampleRate
— Input sample rate in hertz
1200000
(default) | positive real scalar
Specify the input sample rate Fs as a positive real scalar expressed in hertz.
Dependencies
To enable this property, set the NormalizedFrequency
property
to false
.
Data Types: single
| double
Fixed-Point Properties
RoundingMethod
— Rounding method for output fixed-point operations
'Floor'
(default) | 'Ceiling'
| 'Convergent'
| 'Nearest'
| 'Round'
| 'Simplest'
| 'Zero'
Rounding method for output fixed-point operations, specified as a character vector. For more information on the rounding modes, see Precision and Range.
CoefficientsDataType
— Word and fraction lengths of coefficients
numerictype(1,16)
(default) | numerictype
object
Word and fraction lengths of coefficients, specified as a signed or unsigned
numerictype
object. The default,
numerictype(1,16)
corresponds to a signed numeric type object
with 16-bit coefficients and a fraction length determined based on the coefficient
values, to give the best possible precision.
This property is not tunable.
Word length of the output is same as the word length of the input. Fraction length of the output is computed such that the entire dynamic range of the output can be represented without overflow. For details on how the fraction length of the output is computed, see Fixed-Point Precision Rules for Avoiding Overflow in FIR Filters.
Usage
Syntax
Description
Input Arguments
x
— Data input
vector | matrix
Data input, specified as a vector or a matrix. The System object treats a Ki-by-N input matrix as N independent channels, decimating each channel over the first dimension.
The number of input rows Ki can be arbitrary and does not have to be a multiple of the decimation factor.
This object supports variable-size input signals, that is, the frame length (number of rows) of the signal can change even when the object is locked. However, the number of channels (columns) must remain constant.
This object does not support complex unsigned fixed-point data.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
| fi
Complex Number Support: Yes
Output Arguments
y
— Filtered and downsampled signal
vector | matrix
Filtered and downsampled signal, returned as a vector or matrix.
When the input is of size
Ki-by-N, and
Ki is not a multiple of the decimation
factor M, the output signal has an upper bound size of
ceil
(Ki/M)-by-N.
If Ki is a multiple of the decimation
factor, then the output is of size
(Ki/M)-by-N.
The number of channels (columns) does not change.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
| fi
Complex Number Support: Yes
Object Functions
To use an object function, specify the
System object as the first input argument. For
example, to release system resources of a System object named obj
, use
this syntax:
release(obj)
Specific to dsp.CICCompensationDecimator
freqz | Frequency response of discrete-time filter System object |
freqzmr | Compute DTFT approximation of impulse response of multirate or single-rate filter |
filterAnalyzer | Analyze filters with Filter Analyzer app |
info | Information about filter System object |
cost | Estimate cost of implementing filter System object |
coeffs | Returns the filter System object coefficients in a structure |
outputDelay | Determine output delay of single-rate or multirate filter |
polyphase | Polyphase decomposition of multirate filter |
generatehdl | Generate HDL code for quantized DSP filter (requires Filter Design HDL Coder) |
Examples
Impulse and Frequency Response of CIC Compensation Decimator
Create a dsp.CICCompensationDecimator
object with default settings. While creating the object, set the NormalizedFrequency
property to true
so that the passband and the stopband frequencies are in normalized frequency units.
CICCompDecim = dsp.CICCompensationDecimator(...
NormalizedFrequency=true)
CICCompDecim = dsp.CICCompensationDecimator with properties: CICRateChangeFactor: 2 CICNumSections: 2 CICDifferentialDelay: 1 DecimationFactor: 2 NormalizedFrequency: true DesignForMinimumOrder: true PassbandFrequency: 0.1667 StopbandFrequency: 0.6667 PassbandRipple: 0.1000 StopbandAttenuation: 60 Use get to show all properties
Plot the impulse response.
impz(CICCompDecim)
Plot the magnitude and phase responses.
freqz(CICCompDecim)
Compensation Decimator Design
Design a compensation decimator for an existing CIC decimator having six sections and a decimation factor of 6.
CICDecim = dsp.CICDecimator(DecimationFactor=6,...
NumSections=6)
CICDecim = dsp.CICDecimator with properties: DecimationFactor: 6 DifferentialDelay: 1 NumSections: 6 FixedPointDataType: 'Full precision'
Construct the compensation decimator. Specify a decimation factor of 2, an input sample rate of 16 kHz, a passband frequency of 4 kHz, and a stopband frequency of 4.5 kHz.
fs = 16e3; fPass = 4e3; fStop = 4.5e3; CICCompDecim = dsp.CICCompensationDecimator(CICDecim,... DecimationFactor=2,PassbandFrequency=fPass,... StopbandFrequency=fStop,SampleRate=fs)
CICCompDecim = dsp.CICCompensationDecimator with properties: CICRateChangeFactor: 6 CICNumSections: 6 CICDifferentialDelay: 1 DecimationFactor: 2 DesignForMinimumOrder: true PassbandFrequency: 4000 StopbandFrequency: 4500 PassbandRipple: 0.1000 StopbandAttenuation: 60 SampleRate: 16000 Show all properties
Visualize the frequency response of the cascade. Normalize all magnitude responses to 0 dB.
filtCasc = dsp.FilterCascade(CICDecim,CICCompDecim); f = fvtool(CICDecim, CICCompDecim, filtCasc, ... Fs=[fs*6 fs fs*6]); f.NormalizeMagnitudeto1 = 'on'; legend(f,'CIC Decimator','CIC Compensation Decimator', ... 'Overall Response');
Apply the design to a 1200-sample random input signal. Store the decimated output along the first dimension of the y array.
x = dsp.SignalSource(fi(rand(1200,1),1,16,15),SamplesPerFrame=120); y = fi(zeros(100,1),1,32,20); for ind = 1:10 x2 = CICDecim(x()); y(((ind-1)*10)+1:ind*10,1) = CICCompDecim(x2); end
Algorithms
The response of a CIC filter is given by:
R, D, and N are the rate change factor, the differential delay, and the number of sections in the CIC filter, respectively.
After decimation, the CIC response has the form:
The normalized version of this last response is the one that the CIC compensator needs to compensate. Hence, the passband response of the CIC compensator should take the following form:
where ωp is the passband frequency of the CIC compensation filter.
Notice that when ω/2R ≪ π, the previous equation for Hciccomp(ω) can be simplified using the fact that sin(x) ≅ x:
This previous equation is the inverse sinc approximation to the true inverse passband response of the CIC filter.
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Usage notes and limitations:
See System Objects in MATLAB Code Generation (MATLAB Coder).
This object supports code generation for ARM® Cortex®-M and ARM Cortex-A processors.
In the code you generate from this object, the decimator output is a fixed-size signal if the input signal is fixed size and is a multiple of the decimation factor. If the input is not a multiple of the decimation factor or if the input is a variable-size signal, then the decimator output is of variable-size.
HDL Code Generation
Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.
This object supports HDL code generation with the Filter Design HDL Coder™ product. For workflows and limitations, see Generate HDL Code for Filter System Objects (Filter Design HDL Coder).
Version History
Introduced in R2014bR2024a: Support for normalized frequencies
When you set the NormalizedFrequency
property to
true
, you must specify the passband frequency and stopband frequency in
normalized frequency units (0 to 1). For more information, see the NormalizedFrequency
property description.
R2023a: Support for arbitrary input frame length
This object supports an input signal with an arbitrary frame length, so the input frame length does not have to be a multiple of the decimation factor.
R2023a: Support for variable-size input signal
The input signal to this object can be a variable-size signal, that is, the frame length (number of rows) of the signal can change even when the object is locked. However, the number of channels (columns) must remain constant.
See Also
Functions
freqz
|freqzmr
|filterAnalyzer
|info
|cost
|coeffs
|outputDelay
|polyphase
|generatehdl
Objects
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