Call Progress Tone Detector

FX633

© 1996 Consumer Microcircuits Limited

7

D/633/3

1.5.3

Block Diagram Description

(reference Figure 1)

Slicer

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

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 340Hz and

650Hz. The signal to noise ratio must be 16dB or greater. The signal must be consistent over a period

of about 140 ms. These decode criteria are continuously monitored and the assessment is updated

every 7 ms, reference Figure 3.

The analyser samples the call progress signal at 9.3kHz; so care should be taken to avoid high

frequency signals (e.g. 18kHz) aliasing into the call progress band.

Control Logic

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

output pins. See the Decode Output Truth Table in section 1.5.4.

Xtal/Clock Oscillator

If the on-chip Xtal oscillator is to be used, then external components X1, R1, C1 and C2 are 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

DETECT2

DETECT1

CONDITIONS

0

0

No Signal

0

1

Call Progress Low Band:

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

400, 425, 440, and 450Hz tones

1

1

Call Progress High Band:

Will detect 480+620, 600 and 620Hz tones

1

0

Non Call Progress signal, e.g. Voice Activity

Note that DETECT1 responds to the whole range of call progress tones from 340Hz to 650Hz.

1.6

Application Notes

1.6.1

General

On power-up, a logic "0" at the ENABLE input may be used to disable and initialise the

device.