upsample

Upsample discrete-time models

Syntax

sysl = upsample(sys,L)


Description

sysl = upsample(sys,L) resamples the discrete-time dynamic system model sys at a sampling rate that is L-times faster than the sample time of sys (Ts₀). L must be a positive integer. When sys is a TF model, H(z), upsample returns sysl as H(z^L) with the sample time Ts₀ / L.

The responses of models sys and sysl have the following similarities:

• The time responses of sys and sysl match at multiples of Ts₀.

• The frequency responses of sys and sysl match up to the Nyquist frequency π / Ts₀.

Note

sysl has L times as many states as sys.

Examples

Upsample Discrete-Time Transfer Function

Create a transfer function with sample time 2.25 seconds.

sys = tf(0.75,[1 10 2],2.25)

sys =
 
       0.75
  --------------
  z^2 + 10 z + 2
 
Sample time: 2.25 seconds
Discrete-time transfer function.

Create a transfer function with a sample time that is 14 times faster than sys.

L = 14;
sys1 = upsample(sys,L)

sys1 =
 
         0.75
  ------------------
  z^28 + 10 z^14 + 2
 
Sample time: 0.16071 seconds
Discrete-time transfer function.

The sample time of sys1 is 0.16071 seconds, which is 14 times faster than the sample time of sys.