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CMX673D4

Call Progress Tone Detector

CML Microsystems Plc 

1.5.3 Block Diagram Description

Amplifier

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

internally set at ½VDD.

Signal Analyser

The frequency range, quality and consistency of the input signal is analysed 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.

Control Logic

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

output pin. See the Decode Output Truth Table in Section 1.5.4.

Level Detector

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.

Xtal/Clock Oscillator

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

XTALN pin should be left unconnected.

1.5.4 Decode Output Truth Table

“DETECT”

CONDITIONS

0

No Signal

1

Call Progress Band:

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

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

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

Table 1 Decode Output Truth Table

© 2001 Consumer Microcircuits Limited

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D/673/5

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