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CMX673

Call Progress Tone Detector

MX-COM Inc  

Call Progress Tone Detector

Page 6 of 11

CMX673 Preliminary Information

4.2 Glossary

The following Glossary, and the Decode Truth Table in Section 4.4 provide an explanation of the decoding

functions and features offered by the CMX673.

Call Progress Tones:

Call Progress Band:

No Signal:

Nominal:

The single and dual frequency tones in the range 350Hz to 620Hz specified

widely for call progress signaling.

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 is classified by the absence of an input signal, a signal below 250Hz, or

a signal between 750Hz and 10kHz

Note: Signals above 10kHz should be at a level below -38dBm to avoid aliasing.

Subject to dynamic tolerances within the signal analysis process. Absolute

values are not material or adverse to performance.

4.3 Block Diagram Description

Amplifier:

Signal Analyzer:

Control Logic:

Level Detector:

Xtal/Clock Oscillator:

The input signal is amplified by a self-biased inverting amplifier. The DC bias of

this input is internally set at VDD/2.

The frequency range, quality and consistency of the input signal is analyzed by this

functional block. To be classified as a call progress signal the input signal

frequencies should lie between 315Hz and 650Hz. The signal to noise ratio must

be 16dB or greater. The signal must be consistent over a period of about 80ms.

These decode criteria are continuously monitored and the assessment is updated

every 6ms; reference Figure 4.

This block categorizes the nature of the signal into two decoded output states and

controls the output pin. See the Decode Output Truth Table in Section 4.4.

The level detector operates by measuring the level of the amplified input signal and

comparing it with a preset threshold. The level detector output goes to the Control

and Output Logic block. The data output is gated with the level detector’s output.

The data output is valid only if the level detector output is true.

If the on-chip Xtal oscillator is to be used, then external component X1 is required.

If an external clock source is to be used, then it should be connected to the

XTAL/CLOCK input pin and the XTAL pin should be left unconnected.

4.4 Decode Output Truth Table

“DETECT”

0

1

CONDITIONS

No Signal

Call Progress Band:

Will detect 350+440, 400+450, 440+480

400, 425,440, 450, 480+620, 600 and 620Hz tones

Note: DETECT responds to the whole range of call progress tones from 315Hz to 650Hz.

Table 3: Decode Output Truth Table

ã2001 MX-COM, Inc

www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054

Doc. # 20480182.007

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All Trademarks and service marks are held by their respective companies.

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