Hi this is a general question about z-transform and block diagram:(adsbygoogle = window.adsbygoogle || []).push({});

Suppose Y(z) is the output, U(z) is the input, and H(z) is the transfer function, then:

Y(z) = H(z) U(z).

Suppose we start with an open-loop transfer function G(s) under unity feedback, then to go from s to z, say we assume a zero-order-hold component in the open loop path. and obtain G(z) of that path. Then, we compute H(z) by H(z) = G(z) /( 1+G(z) ). Now, we transform the input from U(s) to U(z). We multiply H(z) by U(z) to get Y(z). Once we get Y(z), we could transform it back to Y(s) or to y(t).

Is this correct so far?

My question is, suppose you have two transfer functions in cascade A(s) and B(s), such that the combined transfer function is AB(s), we know that AB(z) does not equal to A(z)B(z), why could I multiply H(z) and U(z) to get Y(z)? Why am I allowed to multiply there?

Is there something wrong in what I said?

- Thanks

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Block diagram in z-domain

Can you offer guidance or do you also need help?

Draft saved
Draft deleted

**Physics Forums | Science Articles, Homework Help, Discussion**