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TEA1111AT

Speech circuit with dialler interface,regulated supply and earpiece volume control

Philips Electronics 

Philips Semiconductors

Speech circuit with dialler interface, regulated

supply and earpiece volume control

Product specification

TEA1111A

Sidetone suppression

The TEA1111A anti-sidetone network comprising

RCC // Zline, Rast1, Rast2, Rast3, RSLPE and Zbal (see Fig.10)

suppresses the transmitted signal in the earpiece.

Maximum compensation is obtained when the following

conditions are fulfilled:

RSLPE × Rast1 = RCC × (Rast2 + Rast3 )

k = -R----a---s--t-2--R--×---a--(s--R-t-1---a-×-s---t-R3----+S---L--R-P---ES----L---P---E----)

Zbal = k × Zline

The scale factor k is chosen to meet the compatibility with

a standard capacitor from the E6 or E12 range for Zbal.

In practice, Zline varies considerably with the line type and

the line length. Therefore, the value of Zbal should be for an

average line length, which gives 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.

The anti-sidetone network for the TEA1111A attenuates

the receive signal from the line by 32 dB before it enters

the receive stage. The attenuation is almost constant over

the whole audio frequency range.

A Wheatstone bridge configuration (see Fig.11) may also

be used.

More information on the balancing of an anti-sidetone

bridge can be obtained in our publication “Semiconductors

for Wired Telecom Systems; Applications Handbook

IC03b”.

For ordering information, please contact the Philips

Semiconductors sales office.

handbook, full pagewidth

Zline

VEE

LN

RCC

Rast1

RSLPE

Im

IR

Rast2

Rast3

SLPE

Zbal

Zir

MBE787

Fig.10 Equivalent circuit of TEA1111A anti-sidetone bridge.

1999 Nov 22

10

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