Note that since the NTF is a discrete-time transfer function, it’s only defined for frequencies from dc to f s /2, whereas the STF is a continuous-time function, and is defined for all frequencies.

Week 2: time/frequency response, mappings between s- and z-planes; Week 3: digitizations of analog designs, limitations on sampling period; Week 4: sampled-data systems, ideal sampler, starred ...

Note that since the NTF is a discrete-time transfer function, it’s only defined for frequencies from dc to f S /2, whereas the STF is a continuous-time function, and is defined for all frequencies.