getFixedPointInfo
Get fixed-point word and fraction lengths
Description
[
returns all the word lengths and fraction lengths of the fixed-point sections and
the output of the CIC filter System objects, WLs
, FLs
] = getFixedPointInfo(cicObj
,nt
)dsp.CICDecimator
and dsp.CICInterpolator
, based on the input numeric type,
nt
. For locked objects or when the
FixedPointDataType
property of the unlocked CIC filter
object is set to 'Specify word and fraction lengths'
, the input
numeric type argument, nt
, is optional.
Examples
Determine the Section and Output Word Lengths and Fraction Lengths
Using the getFixedPointInfo
function, you can determine the word lengths and fraction lengths of the fixed-point sections and the output of the dsp.CICDecimator
and dsp.CICInterpolator
System objects. The data types of the filter sections and the output depend on the FixedPointDataType
property of the filter System object™.
Full precision
Create a dsp.CICDecimator
object. The default value of the NumSections
property is 2. This value indicates that there are two integrator and comb sections. The WLs and FLs vectors returned by the getFixedPointInfo
function contain five elements each. The first two elements represent the two integrator sections. The third and fourth elements represent the two comb sections. The last element represents the filter output.
cicD = dsp.CICDecimator
cicD = dsp.CICDecimator with properties: DecimationFactor: 2 DifferentialDelay: 1 NumSections: 2 FixedPointDataType: 'Full precision'
By default, the FixedPointDataType
property of the object is set to 'Full precision'
. Calling the getFixedPointInfo
function on this object with the input numeric type, nt
, yields the following word length and fraction length vectors.
nt = numerictype(1,16,15)
nt = DataTypeMode: Fixed-point: binary point scaling Signedness: Signed WordLength: 16 FractionLength: 15
[WLs,FLs] = getFixedPointInfo(cicD,nt) %#ok
WLs = 1×5
18 18 18 18 18
FLs = 1×5
15 15 15 15 15
For details on how the word lengths and fraction lengths are computed, see the description for Output Arguments.
If you lock the cicD
object by passing an input to its algorithm, you do not need to pass the nt
argument to the getFixedPointInfo
function.
input = int64(randn(8,1))
input = 8x1 int64 column vector
1
2
-2
1
0
-1
0
0
output = cicD(input)
output = 0 1 3 0 DataTypeMode: Fixed-point: binary point scaling Signedness: Signed WordLength: 66 FractionLength: 0
[WLs,FLs] = getFixedPointInfo(cicD) %#ok
WLs = 1×5
66 66 66 66 66
FLs = 1×5
0 0 0 0 0
The output and section word lengths are the sum of input word length, 64 in this case, and the number of sections, 2. The output and section fraction lengths are 0 since the input is a built-in integer.
Minimum section word lengths
Release the object and change the FixedPointDataType
property to 'Minimum section word lengths'
. Determine the section and output fixed-point information when the input is fixed-point data, fi(randn(8,2),1,24,15)
.
release(cicD);
cicD.FixedPointDataType = 'Minimum section word lengths'
cicD = dsp.CICDecimator with properties: DecimationFactor: 2 DifferentialDelay: 1 NumSections: 2 FixedPointDataType: 'Minimum section word lengths' OutputWordLength: 32
inputF = fi(randn(8,2),1,24,15)
inputF = 3.5784 -0.1241 2.7694 1.4897 -1.3499 1.4090 3.0349 1.4172 0.7254 0.6715 -0.0630 -1.2075 0.7148 0.7172 -0.2050 1.6302 DataTypeMode: Fixed-point: binary point scaling Signedness: Signed WordLength: 24 FractionLength: 15
[WLs, FLs] = getFixedPointInfo(cicD,numerictype(inputF)) %#ok
WLs = 1×5
26 26 26 26 32
FLs = 1×5
15 15 15 15 21
Specify word and fraction lengths
Change the FixedPointDataType
property to 'Specify word and fraction lengths'
. Determine the fixed-point information using the getFixedPointInfo
function.
cicD.FixedPointDataType = 'Specify word and fraction lengths'
cicD = dsp.CICDecimator with properties: DecimationFactor: 2 DifferentialDelay: 1 NumSections: 2 FixedPointDataType: 'Specify word and fraction lengths' SectionWordLengths: [16 16 16 16] SectionFractionLengths: 0 OutputWordLength: 32 OutputFractionLength: 0
[WLs, FLs] = getFixedPointInfo(cicD,numerictype(inputF)) %#ok
WLs = 1×5
16 16 16 16 32
FLs = 1×5
0 0 0 0 0
The section and output word lengths and fraction lengths are assigned as per the respective fixed-point properties of the cicD
object. These values are not determined by the input numeric type. To confirm, call the getFixedPointInfo
function without passing the numerictype
input argument.
[WLs, FLs] = getFixedPointInfo(cicD) %#ok
WLs = 1×5
16 16 16 16 32
FLs = 1×5
0 0 0 0 0
Specify word lengths
To specify the word lengths of the filter section and output, set the FixedPointDataType
property to 'Specify word lengths'
.
cicD.FixedPointDataType = 'Specify word lengths'
cicD = dsp.CICDecimator with properties: DecimationFactor: 2 DifferentialDelay: 1 NumSections: 2 FixedPointDataType: 'Specify word lengths' SectionWordLengths: [16 16 16 16] OutputWordLength: 32
The getFixedPointInfo
function requires the input numeric type because that information is used to compute the section and word fraction lengths.
[WLs, FLs] = getFixedPointInfo(cicD,numerictype(inputF))
WLs = 1×5
16 16 16 16 32
FLs = 1×5
5 5 5 5 21
For more details on how the function computes the word and fraction lengths, see the description for Output Arguments.
Input Arguments
cicObj
— CIC filter System object™
dsp.CICDecimator
| dsp.CICInterpolator
dsp.CICDecimator
dsp.CICInterpolator
CIC filter System object, specified as either a dsp.CICDecimator
or dsp.CICInterpolator
System object.
nt
— Input numeric type
numerictype
Input data numeric type, specified as a numerictype
(Fixed-Point Designer) object.
Specify this input when the System object is unlocked and the FixedPointDataType
property of the CIC filter is set to 'Full precision'
,
'Minimum section word lengths'
, or 'Specify
word lengths'
. If the FixedPointDataType
property is set to 'Specify word and fraction lengths'
,
the word and fraction lengths of the filter sections and the output are
specified through the object parameters. In this case, the
nt
input is optional. Alternatively, if the object
is locked, the fixed-point data input to the object specifies the input word
length and fraction length. The nt
argument in this
case is also optional.
Example: numerictype(1,16,15)
Example: input = fi(randn(16,1),1,32,30); numerictype(input)
Output Arguments
WLs
— Section and output word lengths
row vector
Section and output word lengths, returned as a row vector. The first 2 ×
NumSections
elements in the row vector correspond
to the word lengths of the integrator and comb sections of the CIC filter.
The value of the NumSections
property specifies the
number of sections in either the integrator part or the comb part of the
filter. The last element in the vector corresponds to the word length of the
object output.
The word length of the CIC filter sections and the object output depend on
the FixedPointDataType
property of the CIC filter
object.
Full precision
When the FixedPointDataType
property of the CIC
filter object is set to 'Full precision'
, the section
and output word lengths are computed using the following equation:
where,
WLsection –– Word length of the CIC filter section.
WLoutput –– Word length of the output data.
WLinput –– Word length of the input data.
NumSect –– Number of CIC filter sections specified through the
NumSections
property.
For locked objects, WLinput is
inherited from the data input you pass to the object algorithm. For unlocked
objects, the WLinput is inherited
from the nt
argument.
Minimum section word lengths
When the FixedPointDataType
property is set to
'Minimum section word lengths'
, the section word
length is given by the following equation:
The output word length is the value you specify in
OutputWordLength
property of the CIC filter
object.
Specify word and fraction lengths
When the FixedPointDataType
property is set to
'Specify word and fraction lengths'
, the section
word lengths and output word length are the values you specify in the
SectionWordLengths
and
OutputWordLength
properties of the CIC filter
object.
Specify word lengths
When the FixedPointDataType
property is set to
'Specify word lengths'
, the section word lengths
and the output word length are the values you specify in the
SectionWordLengths
and
OutputWordLength
properties of the CIC filter
object.
Example: [20 20 20 20 20]
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
FLs
— Section and output fraction lengths
row vector
Section and output fraction lengths, returned as a row vector. The first 2
× NumSections
elements in the row vector correspond to
the fraction lengths of the integrator and comb sections of the CIC filter.
The value of NumSections
property specifies the number
of sections in either the integrator part or the comb part of the filter.
The last element in the vector corresponds to the fraction length of the
object output.
The fraction length of the CIC filter sections and the object output
depend on the FixedPointDataType
property of the CIC
filter object.
Full precision
When the FixedPointDataType
property of the CIC
filter object is set to 'Full precision'
, the section
and output fraction lengths are computed using the following
equation:
For inputs of built-in integer data types, the section and output fraction lengths are 0.
Minimum section word lengths
When the FixedPointDataType
property of the CIC
filter object is set to 'Minimum section word lengths'
,
the section and output fraction lengths,
FLsection and
FLoutput are given by the
following equation:
For inputs of built-in integer data types, the section and output fraction lengths are 0.
Specify word and fraction lengths
When the FixedPointDataType
property of the CIC
filter object is set to 'Specify word and fraction
lengths'
, the section and output fraction lengths are the
values you specify in the SectionFractionLengths
and
OutputFractionLength
properties.
Specify word lengths
When the FixedPointDataType
property of the CIC
filter object is set to 'Specify word lengths'
, the
section and output fraction lengths,
FLsection and
FLoutput are given by the
following equation:
Example: [12 12 12 12 12]
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
References
[1] Hogenauer, E.B. "An Economical Class of Digital Filters for Decimation and Interpolation." IEEE Transactions on Acoustics, Speech and Signal Processing. Volume 29, Number 2, 1981, 155–162.
[2] Meyer-Baese, U. Digital Signal Processing with Field Programmable Gate Arrays. New York: Springer, 2001.
[3] Harris, Fredric J. Multirate Signal Processing for Communication Systems. Indianapolis, IN: Prentice Hall PTR, 2004.
Version History
Introduced in R2018a
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