- #1

Razvan

- 53

- 0

One method is to design the controller in the continuous time domain, arriving at a transfer function (in the s-domain). After that, a transfer function for the ADC system must be taken into consideration. I will suppose a zero order hold circuit is used. So, before finding the transfer function in the z-domain, we multiply our initial transfer function with the transfer function of the ZOH circuit (##G_{ZOH}(s) = \frac{1-e^{-sT}}{s}##). After that, we can transform the overall transfer function from the s-domain to the z-domain. After we have the z transfer function, we can design an algorithm to compute the current output based on past input and/or output.

My question is why do we need the ZOH circuit. I think it is because adding it to the system (in the s-domain) we get a simulation of how the discrete system will behave. We force the continuous transfer function to have a constant input throughout one "sampling period". Is this correct? But why do we keep it when converting from s-domain to z-domain?