VIII - TONE DETECTORS

VIII.1 - Overview

The general purpose TS75C520 tone detectors

block is a powerful module that covers a lot of

applications :

- call progress tone detection, fully programmable

for all countries,

- DTMF detection,

- FAX, voice, data automatic detection,

- call waiting detection,while in voice or data mode.

VIII.2 - Description

The tone detectorblock is a set of 16 identical Cells.

Each cell is composed of a Double Biquadratic

Filter, a Power estimator section, a Static level and

a Level comparator.

Each Biquadratic Filter, Power Estimator and Static

Level can be programmed using a complete set of

Commands (TDRC, TDRW, TDWC, TDWW, TDZ).

The wiring between the different Cells can be de-

fined by the user, using the associatedCommand

allowing a wide range of applications.

The 16 Comparator Outputs give, on a baud basis,

the information into two 8 bits words TONEDET0

(for cells number 0 to 7) and TONEDET1 (for cells

number 8 to F). These TONEDET variables can be

accessed using a MR command or, more easily,

monitored on a baud basis using the DOSR com-

mand.

VIII.2.1 - Biquadratic Filters

Each Biquadratic Filter is a double regular section

that can perform any Transfer function with 4 Poles

and 4 Zeros. This routine is run on a sample basis.

Z -1

C0

C5

2

2

CB

C7

C8

C9

CA

C1

C2

C3

C4

Z -1

IN

OUT

C6

Figure 2 : Biquadratic IIR Filter

The corresponding transfer function is :

Out

Input

C5

1

CB

1

± 2 ⋅ C7

Note :

All coefficients are coded on 16 bits 2’s complement in the range +1, -1 (Q15). To avoid the possibility of overflow the user must check

that the internal node must not be higher that 0.5 (in Q15 representation).

ST75C520

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