DC Blocker
Block DC component
Libraries:
DSP System Toolbox /
Signal Operations
DSP System Toolbox HDL Support /
Signal Operations
Description
The DC Blocker block removes the DC component of the input signal. This block supports SIMD code generation. For details, see Code Generation.
Ports
Input
Input — Input signal
scalar  vector  matrix
Specify the input signal that contains the DC component as a scalar, vector, or a matrix. When the input is fixedpoint, it is signed only.
Data Types: single
 double
 int8
 int16
 int32
 fixed point
Complex Number Support: Yes
Output
Output — Output signal with no DC component
scalar  vector  matrix
Output signal with the DC component removed. When the output is fixedpoint, it is signed only.
The size, data type, and complexity of the output signal are the same as that of the input signal.
Data Types: single
 double
 int8
 int16
 int32
 fixed point
Complex Number Support: Yes
Parameters
Algorithm for estimating DC offset — Algorithm for estimating DC offset
IIR
(default)  FIR
 CIC
 Subtract mean
Specify the algorithm used for estimating the DC offset. Select from the following:
IIR
uses a recursive estimate based on a narrow, lowpass elliptic filter. This algorithm typically uses less memory than FIR and is more efficient.FIR
uses a nonrecursive, movingaverage estimate. This algorithm typically uses more memory than IIR and is less efficient.CIC
uses a lowpass filter that does not employ any multipliers. If the algorithm isCIC
, then fixedpoint data must be input to the DC Blocker.Subtract mean
computes the means of the columns of the input matrix and subtracts the means from the input. This method does not retain state between inputs. For example, if the input is[1 2 3 4; 3 4 5 6]
, then the DC Blocker block inSubtract mean
mode outputs[1 1 1 1; 1 1 1 1]
.
Normalized bandwidth of lowpass IIR or CIC filter — Normalized bandwidth
0.001
(default)  real scalar in the range (0 1)
Specify the normalized filter bandwidth as a real scalar greater than 0 and less than 1.
Dependencies
The DC Blocker uses this parameter only when the
estimation algorithm is set to IIR
or
CIC
.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
Order of lowpass IIR elliptic filter — Order of lowpass IIR elliptic filter
6
(default)  integer greater than 3
Specify the filter order of the lowpass IIR elliptic filter as an integer greater than 3.
Dependencies
The DC Blocker uses this parameter only when the
estimation algorithm is set to IIR
.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
Number of past input samples for FIR algorithm — Number of past input samples for FIR algorithm
50
(default)  positive integer
Specify, as a positive integer, the number of samples to use when the
estimation algorithm is set to FIR
.
Dependencies
The DC Blocker uses this parameter only when the
estimation algorithm is set to FIR
.
Data Types: single
 double
View Filter Response — Visualize frequency response
button
Opens the fvtool
and displays the magnitude response
of the DC Blocker. The response is based on the block
parameters. Changes made to these parameters update
fvtool
.
To update the magnitude response while fvtool
is
running, modify the block parameters and click
Apply.
Simulate using — Type of simulation to run
Code generation
(default)  Interpreted execution
Specify the type of simulation to run as one of the following:
Code generation
–– Simulate model using generated C code. The first time you run a simulation, Simulink^{®} generates C code for the block. The C code is reused for subsequent simulations, as long as the model does not change. This option requires additional startup time but provides faster simulation speed thanInterpreted execution
.Interpreted execution
–– Simulate model using the MATLAB^{®} interpreter. This option shortens startup time but has slower simulation speed thanCode generation
.
Block Characteristics
Data Types 

Direct Feedthrough 

Multidimensional Signals 

VariableSize Signals 

ZeroCrossing Detection 

^{a} 
Algorithms
The DC blocker subtracts the DC component from the input signal. You can estimate the DC component by using the IIR, FIR, CIC, or subtract mean algorithm.
IIR
Pass the input signal through an IIR lowpass elliptical filter.
The elliptical IIR filter has a passband ripple of 0.1 dB and a stopband attenuation of 60 dB. You specify the normalized bandwidth and the filter order.
FIR
Pass the input signal through an FIR filter that uses a nonrecursive moving average from a finite number of past input samples.
The FIR filter coefficients are given as ones(1,Length)/Length
, where Length
is the number of past input samples for FIR algorithm. The FIR filter structure is a direct form I transposed structure.
CIC
Pass the input signal through a CIC filter. Because the CIC filter amplifies the signal, the filter gain is estimated and subtracted from the DC estimate.
The Cascaded IntegratorComb (CIC) filter consists of two integratorcomb pairs. These pairs help to ensure that the peak of the first sidelobe of the filter response is attenuated by at least 25 dB relative to the peak of the main lobe. The normalized 3 dB bandwidth is used to calculate the differential delay. The delay is used to determine the gain of the CIC filter. The inverse of the filter gain is used as a multiplier, which is applied to the output of the CIC filter. This ensures that the aggregate gain of the DC estimate is 0 dB.
The following equation characterizes the aggregate magnitude response of the filter and the multiplier:
$$\leftH({e}^{j\omega})\right={\left\frac{\mathrm{sin}(M{\scriptscriptstyle \frac{\pi}{2}}{B}_{norm})}{M\mathrm{sin}({\scriptscriptstyle \frac{\pi}{2}}{B}_{norm})}\right}^{N}$$
B_{norm} is the normalized bandwidth such that 0 < B_{norm} < 1.
M is the differential delay in samples.
N is the number of sections, equal to 2.
Set the differential delay, M, to the smallest integer such that H(e^{jω}) < 1/√2. Once M is known, the gain of the CIC filter is calculated as M^{N}. Therefore, to precisely compensate for the filter gain, the multiplier is set to (1/M)^{N}.
Subtract mean
Compute the mean value of each column of the input signal and subtract the mean from the input. For example, if the input is [1 2 3 4; 3 4 5 6], then a DC Blocker set to this mode outputs [1 1 1 1; 1 1 1 1].
References
[1] Nezami, M.K. “Performance Assessment of Baseband Algorithms for Direct Conversion Tactical Software Defined Receivers: I/Q Imbalance Correction, Image Rejection, DC Removal, and Channelization.” In MILCOM 2002. Proceedings, 369–76. Anaheim, CA, USA: IEEE, 2002.
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.
The DC Blocker block supports SIMD code generation using Intel AVX2
technology when the input signal has a data type of single
or
double
.
The SIMD technology significantly improves the performance of the generated code.
HDL Code Generation
Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.
Note
For a DC Blocker optimized for HDL code generation, see High Performance DC Blocker for FPGA (DSP HDL Toolbox). The DSP HDL Toolbox™ block provides an HDLoptimized algorithm with hardwarefriendly control signals and simulates the latency of the HDL algorithm in Simulink.
HDL Coder™ provides additional configuration options 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.
FixedPoint Conversion
Design and simulate fixedpoint systems using FixedPoint Designer™.
If the input is fixed point, it must be a signed integer or a signed fixed point value with a poweroftwo slope and zero bias.
Version History
Introduced in R2014a
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