Complex to MagnitudeAngle
Compute magnitude and phase angle of complex signal using CORDIC algorithm
Libraries:
DSP HDL Toolbox /
Math Functions
Description
The Complex to MagnitudeAngle block computes the magnitude and phase angle of a complex signal and provides hardwarefriendly control signals. To achieve an efficient HDL implementation, the block uses a pipelined Coordinate Rotation Digital Computer (CORDIC) algorithm.
You can use this block to implement operations such as atan2
in hardware.
Examples
Ports
Input
data — Complex input signal
scalar  vector
Complex 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 block implements the conversion logic in parallel for each element of the vector. The input vector can contain up to 64 elements.
The software supports double
and
single
data types for simulation, but not for HDL code generation.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
 fixed point
Complex Number Support: Yes
valid — Indicates valid input data
scalar
Control signal that indicates if the input data is valid. When
valid is 1
(true
), the
block captures values from the input data port. When
valid is 0
(false
), the
block ignores the values from the input data port.
Data Types: Boolean
Output
Magnitude — Magnitude of the input signal
scalar  vector
Magnitude of the input signal, returned as a scalar, a column vector representing samples in time, or a row vector representing channels. The dimensions of this port match the dimensions of the input data port.
Dependencies
To enable this port, set the Output format parameter to
Magnitude and Angle
or Magnitude
.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
 fixdt([],N,0)
Angle — Angle of the input signal
scalar  vector
Angle of the input signal, returned as a scalar, a column vector representing samples in time, or a row vector representing channels. The dimensions of this port match the dimensions of the input data port.
Dependencies
To enable this port, set the Output format parameter to
Magnitude and Angle
or Angle
.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
 fixdt([],N,0)
valid — Indicates valid output data
scalar
Control signal that indicates if the data from the output
data port is valid. When valid is
1
(true
), the block returns valid data from
the Magnitude and/or Angle ports. When
valid is 0
(false
), the
values from the Magnitude and/or Angle ports
are not valid.
Data Types: Boolean
Parameters
Number of iterations source — Source of number of iterations
Auto
(default)  Property
To set the number of iterations to input WL − 1, select
Auto
. If the input is of data typedouble
orsingle
, the number of iterations is set to 16, by default.To specify the number of iterations by using Number of iterations parameter, select
Property
.
Number of iterations — Number of CORDIC iterations
positive integer
The number of iterations must be less than or equal to input WL − 1. The latency of the block depends on the number of iterations performed. For information about latency, see Latency.
Dependencies
To enable this parameter, set Number of iterations source to
Property
.
Output format — Output signal format
Magnitude and Angle
(default)  Magnitude
 Angle
Use this parameter to specify which output ports are enabled.
To enable the Magnitude and Angle output ports, select
Magnitude and Angle
(default).To enable the Magnitude output port and disable the Angle output port, select
Magnitude
.To enable the Angle output port and disable the Magnitude output port, select
Angle
.
Angle format — Output angle format
Normalized
(default)  Radians
To return the Angle output as a fixedpoint value that normalizes the angles in the range [–1,1], select
Normalized
. For more information see Normalized Angle Format.To return the Angle output as a fixedpoint value in the range [π, π], select
Radians
. When using this block to implement theatan2
function, set this parameter toRadians
.
Scale output — Scales output
on
(default)  off
Select this parameter to multiply the Angle output by the inverse of the CORDIC gain factor. The block implements this gain factor with either CSD logic or a multiplier, according to the Scaling method parameter.
Note
If you clear this parameter and apply the CORDIC gain elsewhere in your design,
you must exclude the π/4 term. Because the quadrant mapping algorithm replaces the
first CORDIC iteration by mapping inputs onto the angle range [0, π/4], the initial
rotation does not contribute a gain term. The gain factor is the product of
cos(atan(2^{n}))
, for
n from 1 to Number of iterations – 1.
Scaling method — Implementation of CORDIC gain scaling
CSD
(default)  Multipliers
When you set this parameter to CSD
, the block implements the
CORDIC gain scaling by using a shiftandadd 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 select Multipliers
, the block
implements the CORDIC gain scaling with a multiplier and increases the latency of the
block by four
cycles.
Dependencies
To enable this parameter, select the Scale output parameter.
Algorithms
CORDIC Algorithm
The CORDIC algorithm is a hardwarefriendly method for performing trigonometric functions. It is an iterative algorithm that approximates the solution by converging toward the ideal point. The block uses CORDIC vectoring mode to iteratively rotate the input onto the real axis.
Givens method for rotating a complex number x+iy by an angle θ is as follows. The direction of rotation, d, is +1 for counterclockwise and −1 for clockwise.
$$\begin{array}{l}{x}_{r}=x\mathrm{cos}\theta dy\mathrm{sin}\theta \\ {y}_{r}=y\mathrm{cos}\theta \text{}+dx\mathrm{sin}\theta \end{array}$$
For a hardware implementation, factor out the cosθ to leave a tanθ term.
$$\begin{array}{l}{x}_{r}=\mathrm{cos}\theta \left(xdy\mathrm{tan}\theta \right)\\ {y}_{r}=\mathrm{cos}\theta \left(y+dx\mathrm{tan}\theta \right)\end{array}$$
To rotate the vector onto the real axis, choose a series of rotations of θ_{n} so that $$\mathrm{tan}{\theta}_{n}={2}^{n}$$. Remove the cosθ term so each iterative rotation uses only shift and add operations.
$$\begin{array}{l}R{x}_{n}={x}_{n1}{d}_{n}{y}_{n1}{2}^{n}\\ R{y}_{n}={y}_{n1}+{d}_{n}{x}_{n1}{2}^{n}\end{array}$$
Combine the missing cosθ terms from each iteration into a constant, and apply it with a single multiplier to the result of the final rotation. The output magnitude is the scaled final value of x. The output angle, z, is the sum of the rotation angles.
$$\begin{array}{l}{x}_{r}=\left(\mathrm{cos}{\theta}_{0}\mathrm{cos}{\theta}_{1}\mathrm{...}\mathrm{cos}{\theta}_{n}\right)R{x}_{N}\\ z={\displaystyle \sum _{0}^{N}{d}_{n}{\theta}_{n}}\end{array}$$
Modified CORDIC Algorithm
The convergence region for the standard CORDIC rotation is ≈±99.7°. To work around this limitation, before doing any rotation, the block maps the input into the [0, π/4] range using this algorithm.
if abs(x) > abs(y) input_mapped = [abs(x), abs(y)]; else input_mapped = [abs(y), abs(x)]; end
Quadrant mapping saves hardware resources and reduces latency by reducing the number of CORDIC pipeline stages by one. The CORDIC gain factor, Kn, therefore does not include the n=0, or cos(π/4)term.
$${K}_{n}=cos{\theta}_{1}\mathrm{...}\mathrm{cos}{\theta}_{n}=\text{cos}(26.565)\cdot \text{cos}(14.036)\cdot \text{cos}(7.125)\cdot \text{cos}(3.576)$$
After the CORDIC iterations are complete, the block adjusts the angle back to its original location. First it adjusts the angle to the correct side of π/4.
if abs(x) > abs(y) angle_unmapped = CORDIC_out; else angle_unmapped = (pi/2)  CORDIC_out; end
if (x < 0) if (y < 0) output_angle =  pi + angle_unmapped; else output_angle = pi  angle_unmapped; else if (y<0) output_angle = angle_unmapped;
Architecture
The block generates a pipelined HDL architecture to maximize throughput. Each CORDIC
iteration is done in one pipeline stage. The gain factor, if enabled, is implemented with
canonical signed digit (CSD) logic by default. Set the Scaling method
parameter to Multipliers
to implement the gain factor with a
multiplier.
If you use vector input, this block replicates this architecture in parallel for each element of the vector.
The following table shows Magnitude and Angle output word length (WL), for particular input word length (WL). FL stands for fractional length used in fixedpoint representation.
Input Word Length  Output Magnitude Word Length 

fixdt(0,WL,FL)  fixdt(0,WL + 2,FL) 
fixdt(1,WL,FL)  fixdt(1,WL + 1,FL) 
Input Word Length  Output Angle Word Length  

fixdt([ ],WL,FL)  Radians  fixdt(1,WL + 3,WL) 
Normalized  fixdt(1,WL + 3,WL+2) 
The CORDIC logic at each pipeline stage implements one iteration. For each pipeline stage, the shift and angle rotation are constants.
When you set Output format to Magnitude
,
the block does not generate HDL code for the angle accumulation and quadrant correction
logic.
Normalized Angle Format
This format normalizes the fixedpoint radian angle values around the unit circle. This use of bits can be more efficient than the use of the range [0, 2π] radians. Also this normalized angle format enables wraparound of angle at 0 or 2π without additional detect and correct logic.
For example, representing the angle with 3 bits results in these normalized values.
The block normalizes the angles across [0, π/4] and maps them to the correct octant at the end of the calculation.
Latency
When the valid input is applied, the block returns valid output after Number of iterations + 4 cycles. The latency is displayed on the block mask.
When you set the Number of iterations source parameter to
Property
, the block shows the latency immediately. When you set
Number of iterations source to Auto
, the block
calculates the latency based on the input port data type and displays the latency when you
update the model.
When you set the Number of iterations source parameter to
Auto
, the number of iterations is input WL − 1, and
the latency is input WL + 3. If the input is of data type
double
or single
, the number of iterations is 16,
and the latency is 20.
Note
When you set the Scaling method parameter to
Multipliers
, the block latency increases by four
cycles.
Performance
Performance was measured for the default configuration, with output scaling disabled and
fixdt(1,16,12)
input. When the generated HDL code is synthesized into
a Xilinx^{®} ZC706 (XC7Z045FFG9002) FPGA, the design achieves 350 MHz
clock frequency. It uses the following
resources.
Resource  Number Used 

LUT  891 
FFS  899 
Xilinx LogiCORE^{®} DSP48  0 
Block RAM (16K)  0 
Critical path  2.792 ns 
When you use a multiplier for the CORDIC gain scaling, the design uses one DSP block and has a shorter critical path. The critical path difference is not significant at this number of bits, but as the size of the data increases, the critical path of the CSD implementation rises faster than the critical path of the multiplier.
Resource  Number Used 

LUT  808 
FFS  956 
Xilinx LogiCORE DSP48  1 
Block RAM (16K)  0 
Critical path  2.574 ns 
Performance of the synthesized HDL code varies depending on your target and synthesis options. When you use vector input, the resource usage is about VectorSize times the scalar resource usage.
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.
This block supports C/C++ code generation for Simulink^{®} accelerator and rapid accelerator modes and for DPI component generation.
HDL Code Generation
Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.
HDL Coder™ provides additional configuration option that affect HDL implementation and synthesized logic.
This block has one default HDL architecture.
ConstrainedOutputPipeline  Number of registers to place at
the outputs by moving existing delays within your design. Distributed
pipelining does not redistribute these registers. The default is

InputPipeline  Number of input pipeline stages
to insert in the generated code. Distributed pipelining and constrained
output pipelining can move these registers. The default is

OutputPipeline  Number of output pipeline stages
to insert in the generated code. Distributed pipelining and constrained
output pipelining can move these registers. The default is

This block supports code generation for complex signals.
Version History
Introduced in R2014bR2022a: Moved to DSP HDL Toolbox from DSP System Toolbox
Before R2022a, this block was named Complex to MagnitudeAngle HDL Optimized and was included in the DSP System Toolbox™ DSP System Toolbox HDL Support library.
R2022a: Option to use multiplier for scale factor
In previous releases, the block implemented the CORDIC gain for hardware by using
shiftandadd logic. To use a multiplier, set the Scaling method
parameter to Multipliers
. To use shiftandadd logic, set this
parameter to CSD
.
R2021b: Highthroughput interface
The block accepts and returns a column vector of elements that represent samples in time. The input vector can contain up to 64 samples.
See Also
Complex to MagnitudeAngle (Simulink)  dsphdl.ComplexToMagnitudeAngle
 atan2
Topics
 HDL QAM Transmitter and Receiver (Communications Toolbox)
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