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dsphdl.ComplexToMagnitudeAngle

Magnitude and phase angle of complex signal

Description

The dsphdl.ComplexToMagnitudeAngle 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 dsphdl.ComplexToMagnitudeAngle 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?

Creation

Description

magAngle = dsphdl.ComplexToMagnitudeAngle returns a dsphdl.ComplexToMagnitudeAngle System object, magAngle, that computes the magnitude and phase angle of a complex input signal.

example

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

Example: magAngle = dsphdl.ComplexToMagnitudeAngle('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.

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. The object implements this gain factor with either CSD logic or a multiplier, according to the ScalingMethod property.

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'.

When you set this property to 'CSD', the object implements the CORDIC gain scaling by using a shift-and-add architecture for the multiply operation. This implementation uses no multiplier resources and may increase the length of the critical path in your design. When you set this property to 'Multipliers', the object implements the CORDIC gain scaling with a multiplier and increases the latency of the object by four cycles.

Dependencies

To enable this property, set the ScaleOutput property to true.

Usage

Description

example

[mag,angle,validOut] = magAngle(X,validIn) converts a scalar or vector of complex values X into their component magnitude and phase angles. validIn and validOut are logical scalars that indicate the validity of the input and output signals, respectively.

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

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

Example: magAngle = dsphdl.ComplextoMagnitudeAngle('OutputValue','Magnitude');

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

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

Example: magAngle = dsphdl.ComplextoMagnitudeAngle('OutputValue','Angle');

Input Arguments

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Input signal, specified as a scalar, a column vector representing samples in time, or a row vector representing channels. Using vector input increases data throughput while using more hardware resources. The object implements the conversion logic in parallel for each element of the vector. The input vector can contain up to 64 elements.

double and single data types are supported for simulation, but not for HDL code generation.

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

Control signal that indicates if the input data is valid. When validIn is 1 (true), the object captures the values from the dataIn argument. When validIn is 0 (false), the object ignores the values from the dataIn argument.

Data Types: logical

Output Arguments

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Magnitude calculated from the complex input signal, returned as a scalar, a column vector representing samples in time, or a row vector representing channels. The dimensions and data type of this argument match the dimensions of the dataIn argument.

Dependencies

To enable this argument, set the OutputValue property to 'Magnitude and Angle' or 'Magnitude'.

Angle calculated from the complex input signal, returned as a scalar, a column vector representing samples in time, or a row vector representing channels. The dimensions and data type of this argument match the dimensions of the dataIn argument. The format of this value depends on the AngleFormat property.

Dependencies

To enable this argument, set the OutputValue property to 'Magnitude and Angle' or 'Angle'.

Control signal that indicates if the output data is valid. When validOut is 1 (true), the object returns valid data from the mag and/or angle arguments. When validOut is 0 (false), values from the mag and/or angle arguments are not valid.

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 dsphdl.ComplextoMagnitudeAngle 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.

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 = dsphdl.ComplexToMagnitudeAngle('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 System object
title('Output from dsphdl.ComplexToMagnitudeAngle')
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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Extended Capabilities

Version History

Introduced in R2014b

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