Signal Demodulation
Michael B. Feldman · 2011
Chapter 3 presents the two methods for obtaining the Hilbert transformer: frequency domain and time domain. In the frequency domain the Fast Fourier transform is used, and in the time domain the phase shift can be implemented by a convolution filter, obtainable by the convolution theorem relating convolution to multiplication in the frequency domain. The chapter describes some modern digital-processing procedures for estimating the instantaneous frequency and instantaneous amplitude of real signals. It deals with two demodulation techniques: the envelope with instantaneous frequency extraction and synchronous signal detection. It also describes the realization of the digital Hilbert transformers in the frequency and time domains. The sources and characteristics of possible distortions, errors, and end-effects are discussed with examples.