Discrete Butterworth filter with varying coefficients
Control System Toolbox / Linear Parameter Varying
The block implements the Tustin discretization of a continuous-time Nth-order Butterworth filter. The result is a digital filter with unit DC gain and varying cutoff frequency.
Use this block and the other blocks in the Linear Parameter Varying library to implement common control elements with variable parameters or coefficients. For more information, see Model Gain-Scheduled Control Systems in Simulink.
u— Filter input
Lowpass filter input signal.
freq— Cutoff frequency
Continuous-time value of the cutoff frequency, specified in rad/s.
y— Filter output
Lowpass filter output signal.
Filter order— Lowpass filter order
Lowpass filter order, specified as a positive integer.
Pre-warping frequency w0 (rad/s)— Pre-warping frequency
Pre-warping frequency, specified as a positive scalar. Discretization of
the continuous-time Butterworth filter can shift the cutoff frequency when
it is close to the Nyquist frequency. To ensure that the analog and digital
filters have matching frequency response near a particular frequency
w0, set this parameter to
w0 = 0 corresponds to the bilinear (Tustin)
transformation without pre-warp:
where Ts is the block sample time, specified with the Sample time Ts parameter.
Sample time Ts— Sample time
Block sample time, specified as a positive scalar. This block does not support inherited sample time, because it requires a specified sample time to compute the discretization of the Butterworth filter.