A digital envelope detection filter for real-time operation

A time-domain method to extract the envelope of an amplitude modulated signal at high speed is presented. This method, the envelope detection filter (EDF), is based on a nonlinear function of two consecutive samples of the input sequence. In spite ofits simplicity, EDF provides a quite good approximation to the analytical signal magnitude for a wide range of signals and conditions. The paper presents the basis of the technique and analyzes the sources of error and its sensitivity to noise and signal bandwidth. Results of experiments with simulated signals are in good agreement with the theoretical model. Furthermore, EDF allows a straightforward implementation using a pipeline of two registers and a memory look-up table. The hardware implementation of EDF has been tested at a 10 MS/s, although current technology could achieve several times this throughput rate. Results obtained with EDF for real data of nondestructive testing experiments, are compared with those provided by the full precision analytical signal magnitude obtained by a software Hilbert transform. In all cases, no significant differences are appreciated between the analytical signal magnitude and the EDF output, which is computed in much less time.