System Objects in DSP System Toolbox that Support Fixed-Point Design

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 MATLAB^® command line.

DSP System Toolbox System Objects That Support Fixed Point

Object	Description
Sources
dsp.SignalSource	Import a variable from the MATLAB workspace
dsp.SineWave	Generate discrete sine wave
Sinks
dsp.ArrayPlot	Display vectors or arrays
dsp.AudioFileWriter	Write audio samples to audio file
dsp.SignalSink	Log MATLAB simulation data
dsp.SpectrumAnalyzer	Display frequency spectrum of time-domain signals
timescope	Display time-domain signals
Adaptive Filters
dsp.LMSFilter	Compute output, error, and weights using LMS adaptive algorithm
Filter Designs
dsp.CICCompensationDecimator	Compensate for CIC filter using a FIR decimator
dsp.CICCompensationInterpolator	Compensate 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.AllpoleFilter	IIR Filter with no zeros
dsp.BiquadFilter	Model biquadratic IIR (SOS) filters
dsp.FIRFilter	Static or time-varying FIR filter
dsp.IIRFilter	Infinite Impulse Response (IIR) filter
Multirate Filters
dsp.CICDecimator	Decimate inputs using a Cascaded Integrator-Comb (CIC) filter
dsp.CICInterpolator	Interpolate inputs using a Cascaded Integrator-Comb (CIC) filter
dsp.FIRDecimator	Filter and downsample input signals
dsp.FIRInterpolator	Upsample and filter input signals
dsp.FIRRateConverter	Upsample, filter, and downsample input signals
dsp.HDLFIRRateConverter	Upsample, filter, and downsample—optimized for HDL code generation
dsp.SubbandAnalysisFilter	Decompose signal into high-frequency and low-frequency subbands
dsp.SubbandSynthesisFilter	Reconstruct a signal from high-frequency and low-frequency subbands
Transforms
dsp.FFT	Compute fast Fourier transform (FFT) of input
dsp.HDLFFT	Compute fast Fourier transform (FFT) of input — optimized for HDL Code generation
dsp.HDLIFFT	Compute inverse fast Fourier transform (IFFT) of input — optimized for HDL Code generation
dsp.IFFT	Compute inverse fast Fourier transform (IFFT) of input
Signal Operations
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.HDLNCO	Generate real or complex sinusoidal signals — optimized for HDL code generation
dsp.NCO	Generate real or complex sinusoidal signals
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.ZeroCrossingDetector	Zero crossing detector
Math Operations
dsp.HDLComplexToMagnitudeAngle	Compute magnitude and phase angle of complex signal—optimized for HDL code generation

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 Configure Components. You also use the Fixed-Point Designer™ numerictype (Fixed-Point Designer) 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 the dsp.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.

Related Topics

• Simulink Blocks in DSP System Toolbox that Support Fixed-Point Design