CMX673 Просмотр технического описания (PDF) - CML Microsystems Plc

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CMX673

Call Progress Tone Detector

CML Microsystems Plc 

1.5 General Description

1.5.1 Overall Function Description

The CMX673 Call Progress Tone Detector uses different tone detection methods from those

commonly found with other products.

Many traditional devices from other suppliers use a bandpass filter followed by an energy

detector. The filter is usually designed to pass input signals with a frequency between about

300Hz and 700Hz, and the amplitudes of signals in this range are then checked against a level

threshold. Any signal of acceptable level in this frequency band is classed as a Call Progress

tone, including signals due to speech and noise. False outputs caused by speech are a common

feature with these products, and background noise may lead to a stuck “detect” output.

The CMX673, by contrast, uses a stochastic signal processing technique based on analysis in

both the frequency and time domains, with signal amplitude forming part of the decision process.

This analysis includes checks on whether the signal has a “profile” which matches international

standards for Call Progress tone, or a profile more likely to match that of speech, noise or no

signal.

The following Glossary, and the Decode Truth Table in Section 1.5.4 provide a simple

explanation of the decoding functions and features offered by the CMX673.

1.5.2 Glossary

Call Progress Tones: The single and dual frequency tones in the range 350Hz to 620Hz

specified widely for call progress signalling.

Call Progress Band: The nominal range 315Hz to 650Hz within which the CMX673 will detect

Call Progress tones. The detection algorithm requires that the tones have the characteristics

typical of Call Progress Tones.

No Signal:

The absence of an input signal or

A signal below 250Hz or

A signal between 750Hz and 10kHz.

Note that signals above 10kHz should be at a level below -38dBm so as to avoid

aliasing.

Nominal: Subject to dynamic tolerances within the signal analysis process. Absolute values are

not material or adverse to performance.

© 2001 Consumer Microcircuits Limited

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D/673/5

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