dsp.NCO System object

Generate real or complex sinusoidal signals

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Description

The numerically controlled oscillator, orNCO, object generates real or complex sinusoidal signals. The amplitude of the generated signal is always 1.

To generate real or complex sinusoidal signals:

Define and set up your NCO System object™. SeeConstruction.
Callstepto generate the signals according to the properties ofdsp.NCO. The behavior ofstepis specific to each object in the toolbox.

Note

Starting in R2016b, instead of using thestep卫理公会教徒d to perform the operation defined by the System object, you can call the object with arguments, as if it were a function. For example,y = step(obj)andy = obj()perform equivalent operations.

Construction

nco = dsp.NCOreturns an NCO System object,nco, that generates a multichannel real or complex sinusoidal signal, with independent frequency and phase in each output channel.

nco = dsp.NCO('PropertyName',PropertyValue,...)returns anNCOSystem object,nco, with each specified property set to the specified value.

Properties

`PhaseIncrementSource`	Source of phase increment Indicate how to specify the phase increment:`Property`or`Input port`. The default is`Input port`.
`PhaseIncrement`	Phase increment Specify the phase increment as an integer scalar. This property applies only when you set thePhaseIncrementSourceproperty to`Property`. The default is`100`.
`PhaseOffsetSource`	Source of phase offset Specify the phase offset as`Property`or`Input port`. The default is`Property`.
`PhaseOffset`	Phase offset Specify the phase offset as an integer scalar. This property applies only when you set thePhaseOffsetSourceproperty to`Property`. The default is`0`.
`Dither`	Enable adding internal dithering to NCO algorithm Set this property to`true`to add internal dithering to the NCO algorithm. Dithering is added using thePN Sequence Generatorfrom the Communications System Toolbox™ product. The default is`true`.
`NumDitherBits`	Number of dither bits Specify the number of dither bits as a positive integer. This property applies only when you set the`Dither`property to`true`. The default is`4`.
`PhaseQuantization`	Enable quantization of accumulated phase Set this property to`true`to enable quantization of the accumulated phase. The default is`true`.
`NumQuantizerAccumulatorBits`	Number of quantizer accumulator bits Specify the number of quantizer accumulator bits as an integer scalar greater than 1 and less than the accumulator word length. This property determines the number of entries in the lookup table of sine values. This property applies only when you set thePhaseQuantizationproperty to`true`. The default is`12`.
`PhaseQuantizationErrorOutputPort`	Enable output of phase quantization error Set this property to`true`to output the phase quantization error. This property applies only when you set thePhaseQuantizationproperty to`true`. The default is`false`.
`Waveform`	Type of output signal Specify the type of the output signal:`Sine`,`Cosine`,`Complex exponential`or`Sine and cosine`. The default is`Sine`.
`SamplesPerFrame`	Number of output samples per frame Specify the number of samples per frame of the output signal. This property applies only when you set thePhaseOffsetSourceproperty to`Property`. The default is`1`. When the`PhaseOffsetSource`property is`Input port`, and thePhaseIncrementSourceproperty is`Property`, the number of rows or frame size of the phase offset input determines the number of samples per frame of the output signal. When you set both thePhaseOffsetSourceandPhaseIncrementSourceproperties to`Input port`, the number of rows in the inputs must be 1, and the samples per frame of the output signal is 1.
`OutputDataType`	Output data type Specify the output data type as`double`,`single`or`Custom`. The default is`Custom`. When you select`Custom`you must also set the`CustomOutputDataType`财产。你可以找到的`CustomOutputDataType`property described under`Fixed-Point Properties`on this page.

Fixed-Point Properties

Methods

info	Characteristic information about generated signal
reset	Reset accumulator of NCO object
step	产生多通道真实的或复杂的正弦ignal using NCO (Numerically Controlled Oscillator)

Common to All System Objects
`release`	Allow System object property value changes

Examples

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Design an NCO Source

Open Live Script

Note: This example runs only in R2016b or later. If you are using an earlier release, replace each call to the function with the equivalentstepsyntax. For example, myObject() becomes step(myObject).

Design an NCO source according to given specifications.

df = 0.05;% Frequency resolution = 0.05 HzminSFDR = 96;% Spurious free dynamic range >= 96 dBTs = 1/8000;% Sample period = 1/8000 secdphi = pi/2;% Desired phase offset = pi/2;

Calculate number of accumulator bits required for the given frequency resolution.

Nacc = ceil(log2(1/(df*Ts)));

Actual frequency resolution achieved.

actdf = 1/(Ts*2^Nacc);

Calculate number of quantized accumulator bits required from the SFDR requirement

Nqacc = ceil((minSFDR-12)/6);

Calculate the phase offset

phOffset = 2^Nacc*dphi/(2*pi);

Design the NCO source.

nco = dsp.NCO('PhaseOffset', phOffset,...'NumDitherBits', 4,...'NumQuantizerAccumulatorBits', Nqacc,...'SamplesPerFrame', 1/Ts,...'CustomAccumulatorDataType', numerictype([],Nacc)); san = dsp.SpectrumAnalyzer('SampleRate', 1/Ts,...'PlotAsTwoSidedSpectrum', false);

View the output of the NCO source on a spectrum analyzer. Change the output frequency in the middle of the simulation from 510 Hz to 1520 Hz.

tic;whiletoc < 10iftoc < 5 F0 = 510;elseF0 = 1520;end% Calculate the phase incrementphIncr = int32(round(F0*Ts*2^Nacc)); y = nco(phIncr); san(y);end

Algorithms

This object implements the algorithm, inputs, and outputs described on theNCOblock reference page. The object properties correspond to the block properties, except:

There is no object property that corresponds to theSample timeblock parameter. The objects assumes a sample time of one second.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

SeeSystem Objects in MATLAB Code Generation(MATLAB Coder).

`RoundingMethod`	Rounding method for fixed-point operations This constant property has a value`Floor`.
`OverflowAction`	Overflow action for fixed-point operations This constant property has a value`Wrap`.
`AccumulatorDataType`	Accumulator word and fraction lengths This constant property has a value`Custom`.
`CustomAccumulatorDataType`	Accumulator word and fraction lengths Specify the accumulator fixed-point type as an unscaled`numerictype`object with a`Signedness`of`Auto`. The default is`numerictype([],16)`.
`CustomOutputDataType`	Output word and fraction lengths Specify the output fixed-point type as a scaled`numerictype`object with a`Signedness`of`Auto`. This property applies only when you set theOutputDataTypeproperty to`Custom`. The default is`numerictype([],16,14)`.

Documentation

dsp.NCO System object

Description

Note

Construction

Properties

Methods

Examples

Design an NCO Source

Algorithms

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

See Also

Introduced in R2012a

DSP System Toolbox Documentation

万博1manbetx

Try MATLAB, Simulink, and Other Products

Documentation

dsp.NCO System object

Description

Note

Construction

Properties

Methods

Examples

Design an NCO Source

Algorithms

Extended Capabilities

C/C++ Code GenerationGenerate C and C++ code using MATLAB® Coder™.

See Also

Introduced in R2012a

DSP System Toolbox Documentation

万博1manbetx

Try MATLAB, Simulink, and Other Products

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.