Determine Frequency Response of Zero Order Hold and First Order Hold using Actual Transfer Functions and Pade Approximations 
References
Books
Katsuhiko Ogata - Discrete-Time Control Systems (Second Edition, Prentice Hall)
M. Gopal - Digital Control and State Variable Methods (Second Edition, Tata McGraw-Hill)
Video Lectures
Click here for NPTEL Lecture on Digital Control Systems
("Lecture 4: Data Reconstruction", Module 1: Introduction to Digital Control)