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UBA2050

One-chip telephone ICs with speech, dialler and ringer functions

Philips Electronics 

Philips Semiconductors

One-chip telephone ICs with speech,

dialler and ringer functions

Product specification

UBA2050(A); UBA2051(A;C)

SIDETONE SUPPRESSION

The anti-sidetone network for the UBA205xx, comprising

RCC in parallel with Zline, Rast1, Rast2, Rast3, RSLPE and Zbal

(see Fig.16), 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(--tR-1----a×--s---tR-3----S+---L--RP---E-S---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

chosen 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 UBA205xx attenuates

the received 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.17) may also

be used.

More information on the balancing of an anti-sidetone

bridge can be obtained in our publication “Application

Handbook for Wired Telecom Systems, IC03b”.

handbook, full pagewidth

Zline

GND

LN

RCC

Rast1

RSLPE

Im

IR

Zir

Rast2

Rast3

SLPE

Z bal

MGT046

Fig.16 Equivalent circuit of UBA205xx anti-sidetone bridge.

2000 May 19

16

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