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Fixed-Point Support for MATLAB System Objects in DSP System Toolbox

Get Information About Fixed-Point System Objects

System objects that support fixed-point data processing have fixed-point properties. When you display the properties of a System object™, click show all properties at the end of the property list to display the fixed-point properties for that object. You can also display the fixed-point properties for a particular object by typing dsp.<ObjectName>.helpFixedPoint at the command line.

DSP System Toolbox System Objects That Support Fixed Point

ObjectDescription
Sources
dsp.SignalSource Import a variable from the MATLAB workspace
dsp.SineWaveGenerate discrete sine wave
Sinks
dsp.ArrayPlot

Display vectors or arrays

dsp.AudioFileWriter

Write audio samples to audio file

dsp.SignalSinkLog MATLAB simulation data
dsp.SpectrumAnalyzer

Display frequency spectrum of time-domain signals

dsp.TimeScopeDisplay time-domain signals
Adaptive Filters
dsp.LMSFilterCompute output, error, and weights using LMS adaptive algorithm
Filter Designs
dsp.CICCompensationDecimatorCompensate for CIC filter using a FIR decimator
dsp.CICCompensationInterpolatorCompensate for CIC filter using a FIR interpolator
dsp.Differentiator

Direct form FIR full band differentiator filter

dsp.FIRHalfbandDecimator

Halfband decimator

dsp.FIRHalfbandInterpolator

Halfband interpolator

dsp.HighpassFilter

FIR or IIR highpass filter

dsp.LowpassFilter

FIR or IIR lowpass filter

Filter Implementations
dsp.AllpoleFilterIIR Filter with no zeros
dsp.BiquadFilterModel biquadratic IIR (SOS) filters
dsp.FIRFilterStatic or time-varying FIR filter
dsp.IIRFilterInfinite Impulse Response (IIR) filter
Multirate Filters
dsp.CICDecimatorDecimate inputs using a Cascaded Integrator-Comb (CIC) filter
dsp.CICInterpolator Interpolate inputs using a Cascaded Integrator-Comb (CIC) filter
dsp.FIRDecimatorFilter and downsample input signals
dsp.FIRInterpolatorUpsample and filter input signals
dsp.FIRRateConverterUpsample, filter, and downsample input signals
dsp.HDLFIRRateConverter

Upsample, filter, and downsample—optimized for HDL code generation

dsp.SubbandAnalysisFilterDecompose signal into high-frequency and low-frequency subbands
dsp.SubbandSynthesisFilter Reconstruct a signal from high-frequency and low-frequency subbands
Linear Prediction
dsp.LevinsonSolverSolve linear system of equations using Levinson-Durbin recursion
Transforms
dsp.DCTCompute discrete cosine transform (DCT) of input
dsp.FFTCompute fast Fourier transform (FFT) of input
dsp.HDLFFTCompute fast Fourier transform (FFT) of input — optimized for HDL Code generation
dsp.HDLIFFTCompute inverse fast Fourier transform (IFFT) of input — optimized for HDL Code generation
dsp.IDCTCompute inverse discrete cosine transform (IDCT) of input
dsp.IFFTCompute inverse fast Fourier transform (IFFT) of input
Statistics
dsp.AutocorrelatorCompute autocorrelation of vector inputs
dsp.CrosscorrelatorCompute cross-correlation of two inputs
dsp.HistogramOutput histogram of an input or sequence of inputs
dsp.MaximumCompute maximum value in input
dsp.MeanCompute average or mean value in input
dsp.MedianCompute median value in input
dsp.MinimumCompute minimum value in input
dsp.VarianceCompute variance of input or sequence of inputs
Quantizers
dsp.ScalarQuantizerDecoderConvert each index value into quantized output value
dsp.ScalarQuantizerEncoderPerform scalar quantization encoding
dsp.VectorQuantizerDecoderFind vector quantizer codeword for given index value
dsp.VectorQuantizerEncoderPerform vector quantization encoding
Signal Operations
dsp.ConvolverCompute convolution of two inputs
dsp.DCBlocker

Remove DC component

dsp.Delay

Delay input by specified number of samples or frames

dsp.DigitalDownConverter

Translate digital signal from Intermediate Frequency (IF) band to baseband and decimate it

dsp.DigitalUpConverter

Interpolate digital signal and translate it from baseband to Intermediate Frequency (IF) band

dsp.FarrowRateConverter

Polynomial sample rate converter with arbitrary conversion factor

dsp.HDLNCOGenerate real or complex sinusoidal signals — optimized for HDL code generation
dsp.NCOGenerate real or complex sinusoidal signals
dsp.PeakFinderDetermine extrema (maxima or minima) in input signal
dsp.VariableFractionalDelay

Delay input by time-varying fractional number of sample periods

dsp.VariableIntegerDelay

Delay input by time-varying integer number of sample periods

dsp.WindowWindow object
dsp.ZeroCrossingDetector

Zero crossing detector

Math Operations
dsp.CumulativeProduct Compute cumulative product of channel, column, or row elements
dsp.CumulativeSumCompute cumulative sum of channel, column, or row elements
dsp.HDLComplexToMagnitudeAngle

Compute magnitude and phase angle of complex signal—optimized for HDL code generation

dsp.NormalizerNormalize input
Matrix Operations
dsp.ArrayVectorAdderAdd vector to array along specified dimension
dsp.ArrayVectorDividerDivide array by vector along specified dimension
dsp.ArrayVectorMultiplierMultiply array by vector along specified dimension
dsp.ArrayVectorSubtractorSubtract vector from array along specified dimension
Matrix Factorizations
dsp.LDLFactorFactor square Hermitian positive definite matrices into lower, upper, and diagonal components
dsp.LUFactorFactor square matrix into lower and upper triangular matrices
Linear System Solvers
dsp.LowerTriangularSolverSolve LX = B for X when L is lower triangular matrix
dsp.UpperTriangularSolverSolve UX = B for X when U is upper triangular matrix
Switches and Counters
dsp.CounterCount up or down through specified range of numbers
Buffers
dsp.BufferBuffer an input signal

Set System Object Fixed-Point Properties

Several properties affect the fixed-point data processing used by a System object. Objects perform fixed-point processing and use the current fixed-point property settings when they receive fixed-point input.

You change the values of fixed-point properties in the same way as you change any System object property value. See Component Properties (MATLAB). You also use the Fixed-Point Designer™ numerictype object to specify the desired data type as fixed point, the signedness, and the word- and fraction-lengths. System objects support these values of DataTypeMode: Boolean, Double, Single, and Fixed-point: binary point scaling.

In the same way as for blocks, the data type properties of many System objects can set the appropriate word lengths and scalings automatically by using full precision. System objects assume that the target specified on the Configuration Parameters Hardware Implementation target is ASIC/FPGA.

If you have not set the property that activates a dependent property and you attempt to change that dependent property, a warning message displays. For example, for thedsp.FFT object, before you set CustomOutputDataType to numerictype(1,32,30),set OutputDataType to 'Custom'.

Note

System objects do not support fixed-point word lengths greater than 128 bits.

For any System object provided in the Toolbox, the fimath settings for any fimath attached to a fi input or a fi property are ignored. Outputs from a System object never have an attached fimath.

Full Precision for Fixed-Point System Objects

FullPrecisionOverride is a convenience property that, when you set to true, automatically sets the appropriate properties for an object to use full-precision to process fixed-point input. For System objects, full precision, fixed-point operation refers to growing just enough additional bits to compute the ideal full precision result. This operation has no minimum or maximum range overflow nor any precision loss due to rounding or underflow. It is also independent of any hardware-specific settings. The data types chosen are based only on known data type ranges and not on actual numeric values. Full precision for System objects does not optimize coefficient values.

When you set the FullPrecisionOverride property to true, the other fixed-point properties it controls no longer apply and any of their non-default values are ignored. These properties are also hidden. To specify individual fixed-point properties, first set FullPrecisionOverride to false.

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