Circuit and method for detecting ac voltage pulses

Abstract

A detection circuit and method for detecting AC voltage pulses at a defined frequency relate to first transforming an input signal to a low-frequency signal by multiplying the input signal by a mixing frequency. This down-mixed signal can then be filtered and evaluated. The circuit is particularly suitable for identifying charge unit signals in the telephone network.

Description

PRIORITY INFORMATION [0001] This application is a Continuation of U.S. Application Ser. No. 10 / 431,901, filed May 8, 2003, now published as U.S. Patent Application Publication No. 2003 / 0207677 A1 on Nov. 6, 2003, which application and publication are incorporated herein by reference.BACKGROUND Field of the Invention [0002] The invention relates to a circuit for detecting AC voltage pulses at a defined frequency, to a telephone having such a circuit, and to a method for identifying AC voltage pulses at a defined frequency. [0003] In the European analog telephone network, charge unit pulses are transmitted to the subscriber terminals, in order to allow the accumulating charges to be detected at the subscriber end. The charge unit pulses are short AC voltage pulses at a frequency of 16 kHz, or in some countries at about 12 kHz. These charge pulses must be identified and counted in the subscriber device. [0004] Originally, the charge unit signals were output from the reception path by a...

AI Technical Summary

Benefits of technology

[0007] In particular, it is an object of the invention to further reduce the number of discrete components required to detect AC voltage pulses at a defined frequency.

[0043] The inventive method allows completely digital selective identification of various types of AC voltage pulses. In the method, the input signal is down-mixed to low frequencies by being multiplied by different mixing frequency signals. First, this has the advantage that the signal can be filtered considerably more easily in the low-frequency intermediate frequency band than in the original input signal frequency band. A further advantage is that it is possible to use considerably lower signal rates once the input signal has been transformed to the low-frequency band. This means that less powerful signal processors can be used and that the power consumption of the circuit is reduced.

Problems solved by technology

This solution has the disadvantage of requiring a relatively large number of discrete components for outputting and bandpass filtering the charge unit signals.

Discrete components are expensive and impede further miniaturization of the subscriber terminals.

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