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dsp.HDLComplexToMagnitudeAngle

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

Description

The dsp.HDLComplexToMagnitudeAngle System object™ computes the magnitude and phase angle of a complex signal. It provides hardware-friendly control signals. The System object uses a pipelined coordinate rotation digital computer (CORDIC) algorithm to achieve an HDL-optimized implementation.

To compute the magnitude and phase angle of a complex signal:

  1. Create the dsp.HDLComplexToMagnitudeAngle object and set its properties.

  2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects? (MATLAB).

Creation

Syntax

HCMA = dsp.HDLComplexToMagnitudeAngle
HCMA = dsp.HDLComplexToMagnitudeAngle(Name,Value)

Description

HCMA = dsp.HDLComplexToMagnitudeAngle returns a dsp.HDLComplexToMagnitudeAngle System object, HCMA, that computes the magnitude and phase angle of a complex input signal.

example

HCMA = dsp.HDLComplexToMagnitudeAngle(Name,Value) sets properties of HCMA using one or more name-value pairs. Enclose each property name in single quotes.

Example: cma = dsp.HDLComplexToMagnitudeAngle('AngleFormat','Radians')

Properties

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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 (MATLAB).

Type of output values to return, specified as 'Magnitude and angle', 'Magnitude', or 'Angle'. You can choose for the object to return the magnitude of the input signal, or the phase angle of the input signal, or both.

Format of the phase angle output value from the object, specified as:

  • 'Normalized' — Fixed-point format that normalizes the angle in the range [–1,1].

  • 'Radians' — Fixed-point values in the range [π,−π].

Scale output by the inverse of the CORDIC gain factor, specified as true or false.

Note

If your design includes a gain factor later in the datapath, you can set ScaleOutput to false, and include the CORDIC gain factor in the later gain. For calculation of this gain factor, see Algorithm. The object replaces the first CORDIC iteration by mapping the input value onto the angle range [0,π/4]. Therefore, the initial rotation does not contribute a gain term.

Source of the NumIterations property for the CORDIC algorithm, specified as:

  • 'Auto' — Sets the number of iterations to one less than the input word length. If the input is double or single, the number of iterations is 16.

  • 'Property' — Uses the NumIterations property.

For details of the CORDIC algorithm, see Algorithm.

Number of CORDIC iterations that the object executes, specified as an integer. The number of iterations must be less than or equal to one less than the input word length.

For details of the CORDIC algorithm, see Algorithm.

Dependencies

To enable this property, set NumIterationsSource to 'Property'.

Usage

For versions earlier than R2016b, use the step function to run the System object algorithm. The arguments to step are the object you created, followed by the arguments shown in this section.

For example, y = step(obj,x) and y = obj(x) perform equivalent operations.

Syntax

[mag,angle,validOut] = HCMA(X,validIn)
[mag,validOut] = HCMA(X,validIn)
[angle,validOut] = HCMA(X,validIn)

Description

example

[mag,angle,validOut] = HCMA(X,validIn) converts complex scalar X into its component magnitude and phase angle. validIn and validOut are logical scalars that indicate the validity of the input and output signals, respectively.

[mag,validOut] = HCMA(X,validIn) returns only the component magnitude of X.

To use this syntax, set OutputValue to 'Magnitude'.

Example: HCMA = dsp.HDLComplextoMagnitudeAngle('OutputValue','Magnitude');

[angle,validOut] = HCMA(X,validIn) returns only the component phase angle of X.

To use this syntax, set OutputValue to 'Angle'.

Example: HCMA = dsp.HDLComplextoMagnitudeAngle('OutputValue','Angle');

Input Arguments

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Input signal, specified as a complex scalar value. double and single are allowed for simulation but not for HDL code generation.

Data Types: fi | int8 | int16 | int32 | uint8 | uint16 | uint32 | single | double
Complex Number Support: Yes

Validity of the input signal, specified as a logical scalar.

Data Types: logical

Output Arguments

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Magnitude calculated from the complex input signal, returned as a scalar value with the same data type as the input signal.

Angle calculated from the complex input signal, returned as a scalar value with the same data type as the input signal. The format of this value depends on the AngleFormat property.

Validity of the output components, returned as a logical scalar.

Data Types: logical

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)

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stepRun System object algorithm
releaseRelease resources and allow changes to System object property values and input characteristics
resetReset internal states of System object

Examples

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Use the dsp.HDLComplextoMagnitudeAngle object to compute the magnitude and phase angle of a complex signal. The object uses a CORDIC algorithm for an efficient hardware implementation.

Choose word lengths and create random complex input signal. Then, convert the input signal to fixed-point.

a = -4;
b = 4;
inputWL = 16;
inputFL = 12;
numSamples = 10;
reData = ((b-a).*rand(numSamples,1)+a);
imData = ((b-a).*rand(numSamples,1)+a);
dataIn = (fi(reData+imData*1i,1,inputWL,inputFL));
figure
plot(dataIn)
title('Random Complex Input Data')
xlabel('Real')
ylabel('Imaginary')

Write a function that creates and calls the System object™. You can generate HDL from this function.

Note: This object syntax runs only in R2016b or later. If you are using an earlier release, replace each call of an object with the equivalent step syntax. For example, replace myObject(x) with step(myObject,x).

function [mag,angle,validOut] = Complex2MagAngle(yIn,validIn)
%Complex2MagAngle 
% Converts one sample of complex data to magnitude and angle data.
% yIn is a fixed-point complex number.
% validIn is a logical scalar value.
% You can generate HDL code from this function.

  persistent cma;
  if isempty(cma)
    cma = dsp.HDLComplexToMagnitudeAngle('AngleFormat','Radians');
  end   
  [mag,angle,validOut] = cma(yIn,validIn);
end


The number of CORDIC iterations determines the latency that the object takes to compute the answer for each input sample. The latency is NumIterations+4. In this example, NumIterationsSource is set to the default, 'Auto', so the object uses inputWL-1 iterations. The latency is inputWL+3.

latency = inputWL+3;
mag = zeros(1,numSamples+latency);
ang = zeros(1,numSamples+latency);
validOut = false(1,numSamples+latency);

Call the function to convert each sample. After you apply all input samples, continue calling the function with invalid input to flush remaining output samples.

for ii = 1:1:numSamples
   [mag(ii),ang(ii),validOut] = Complex2MagAngle(dataIn(ii),true);
end
for ii = (numSamples+1):1:(numSamples+latency)
   [mag(ii),ang(ii),validOut(ii)] = Complex2MagAngle(fi(0+0*1i,1,inputWL,inputFL),false);
end
% Remove invalid output values
mag = mag(validOut == 1);
ang = ang(validOut == 1);
figure
polar(ang,mag,'--r')   % Red is output from HDL-optimized System object
title('Output from dsp.HDLComplexToMagnitudeAngle')
magD = abs(dataIn);
angD = angle(dataIn);
figure
polar(angD,magD,'--b') % Blue is output from abs and angle functions
title('Output from abs and angle Functions')

Algorithms

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Introduced in R2014b