Windowed FIR filter (frequency controlled)#

The Windowed FIR filter (frequency controlled) block implements the filter model with final pulse characteristic (FIR filter) with window filter overlay to smooth the amplitude-frequency response (AFC) of FIR filter. The transfer function of FIR filter is as follows (1):

(1)#\[ H(z)\ =\ b_0+b_1z^{-1}+...\ +b_nz^{-n}=\ \sum_{i=0}^{N}{b_iz^{-i}} \]

where:

\(b_N\) – direct connection coefficients that are applied to the input signal;

\(N\) – is the number of delay lines for the input signal;

\(z^{-i}\) – signal delay for i-samples.

The order of FIR filter is always one less than the number of coefficients in the filter transfer function and equal to N.

The structural diagram of FIR filter is shown in the Fig. 1 :

The block allows to select one of the types of filtering:

Bandpass filter - passes the frequency band between the lower and upper cut-off frequencies.

Band-stop filter - does not pass frequencies between the lower and upper cut-off frequencies, but passes vibrations that go beyond these frequencies.

Note

The cut-off frequency shall be less than the Nyquist frequency (half the design sampling frequency).

On the Fig. 2 shows AFC for different types of filtration.

The block allows to specify three different types of sampling:

Fundamental project frequency decimation - the output signal has a sampling rate k times less than the sampling rate of the project (the inverse of the integration step). Here, k is a given design fundamental sampling rate decimation factor, k ≥ 1.

Sample time is the interval between time points at which the input signal values are sampled. The value of the specified sampling period shall be a multiple of the integration step specified in the project.

Sampling frequency - sampling rate of input signal values. The value of the specified sampling frequency shall be a divider of the sampling frequency specified in the design (the value opposite to the integration step).

1. Properties#

Property	Default Value	Description	Units of measurement
Filter order	2	-	-
Sampling type: Fundamental project frequency decimation; Sample time; Sampling frequency	Fundamental project frequency decimation	-	-
Decimation factor of project fundamental discretization frequency, available when selecting `Sampling type` - `Fundamental project frequency decimation`	2	-	-
Sample time, available when selecting `Sampling type` - `Sample time`	0.05	-	s
Sampling frequency, available when selecting `Sampling type` - `Sampling frequency`	5.0	-	Hz
Filter type: Low-pass filter; High pass filter; Band-pass filter; Band-stop filter	Low-pass filter	-	-
High cutoff frequency, available when selecting `Filter type` - `Low-pass filter` or `Band-pass filter`, or `Band-stop filter`	5.0	-	Hz
Initial output signal value	0.0	-	-
Kaiser window width, available when selecting `Sampling type` - `Sampling frequency`	3.0	-	-
Low cutoff frequency, available when selecting `Filter type` - `High pass filter` or `Band-pass filter`, or `Band-stop filter`	2.0	-	Hz

Parameters	Input/Output	Description	Units of measurement	Port type
Original signal	Input	-	-	Automation
Output signal	Output	-	-	Automation

In order to see the connection capabilities of the block, you need to go to page Description of block ports