TEA1064AT View Datasheet(PDF) - Philips Electronics

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TEA1064AT

Low voltage versatile telephone transmission circuit with dialler interface and transmit level dynamic limiting

Philips Electronics 

Philips Semiconductors

Low voltage versatile telephone transmission circuit

with dialler interface and transmit level dynamic limiting

Product specification

TEA1064A

R2, R3, R8, R9 and Zbal (see Fig.18). Maximum

compensation is obtained when the following conditions

are fulfilled:

a) R9 × R2 = R1 × (R3 + [R8//Zbal])

b) (Zbal/[Zbal + R8]) = (Zline/[Zline + R1])

If fixed values are chosen for R1, R2, R3 and R9, then

condition a) is always fulfilled provided R8//Zbal << R3.

To obtain optimum sidetone suppression, condition b) has

to be fulfilled, resulting in:

Zbal = (R8/R1) × Zline = k × Zline

where k is a scale factor; k = (R8/R1).

The scale factor k (value of R8) is chosen to meet the

following criteria:

• compatibility with a standard capacitor from the E6 or

E12 range for Zbal;

• Zbal//R8  << R3 to fulfil condition a) and thus ensure

correct anti-sidetone bridge operation;

• Zbal + R8  >> R9 to avoid influencing the transmit gain.

In practice Zline varies considerably with the line length and

line type. Therefore the value chosen for Zbal should be for

an average line length giving satisfactory sidetone

suppression with short and long lines. The suppression

also depends on the accuracy of the match between

Zbal and the impedance of the average line.

Example

The line impedance for which optimum suppression is to

be obtained can be represented by

210 Ω + (1265 Ω // 140 nF). This represents a 5 km line of

0.5 mm diameter copper twisted-pair cable matched with

600 Ω (176 Ω/km; 38 nF/km).

With k = 0.64 this results in: R8 = 390 Ω;

Zbal = 130 Ω + (820 Ω // 220 nF).

The anti-sidetone network for the TEA1060 family shown

in Fig.18 attenuates the signal received from the line by

32 dB before it enters the receiving amplifier. The

attenuation is almost constant over the whole

audio-frequency range.

Alternatively a conventional Wheatstone bridge can be

used as an anti-sidetone circuit (Fig.19). Both bridge types

can be used with either resistive or complex set

impedances. (More information on the balancing of

anti-sidetone bridges can be obtained in our publication

“Versatile speech transmission ICs for electronic

telephone sets”, order number 9398 341 10011).

Notes

1. The reference used for the MUTE, DTMF and PD

inputs is SLPE.

2. A LOW level for any of these pins is defined by

connection to SLPE, a HIGH level is defined as a

voltage greater than VSLPE + 1.5 V and smaller than

VCC1 + 0.4 V.

March 1994

15

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