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

[0014] The use of the superheterodyne principle for detecting AC voltage pulses at a defined frequency means that there is no need for filter arrangements with discrete components. The signal processing is carried out completely digitally and can be carried out by digital signal processors, thus allowing the evaluation circuit to be implemented in a space-saving and cost-effective manner.

[0015] According to one advantageous embodiment of the invention, the circuit for detecting AC voltage pulses has at least one decimation stage, which reduces the signal rate by omitting sample values. Decimation stages such as these allow the sampling rate for the sample values to be reduced in steps; the actual signal processing can then be carried out at a lower sampling frequency. More processing time is thus available for signal processing for each sample value, and the requirements for the performance of the digital signal processor or of the digital evaluation circuit can therefore be made less stringent. A further advantage of a low processing frequency is that the power consumption of the DSP or of the evaluation 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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