Ringing signal generator employing delta-modulation power amplification

Abstract

A ringing signal generator is disclosed in which a low-level reference ringing signal, generated by a reference waveform generator (101), is amplified by a delta-modulation power amplifier (106, 108). The low-level reference signal is digitally encoded using delta-modulation techniques to generate a high-level digital signal. The high-level digital signal is filtered (421) to remove the high-frequency components therefrom and to decode the digital signal to form the high-level ringing signal that has the same shape and frequency as the reference signal. The delta-modulation power amplifier generates the ringing signal by comparing (401) the reference ringing signal (E.sub.i) with an analog feedback signal (E.sub.f) reconstructed from the high-level digital signal. The resultant binary error signal (E.sub..epsilon.), representing the polarity of the difference between the reference and the feedback signals, is applied to a logic circuit (405) which samples the error signal at a clock rate substantially higher than the frequency of the ringing signal, and generates two binary control signals (+SW, -SW) based upon the error signal at multiple clock instants. These control signals open and close the switching elements (411, 412, 413, 414) in a bridge switch (410) to generate the high-level digital signal.