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UBA1707

Cordless telephone, answering machine line interface

Philips Electronics 

Philips Semiconductors

Cordless telephone, answering machine

line interface

Product specification

UBA1707

handbook, full pagewidth

Bit names are given in italics.

RXI

2Vd

RXM

VI

2Vd

from AGC

IV

RXO

UBA1707

MGK711

Fig.9 Receive amplifier.

SIDETONE SUPPRESSION

The UBA1707 anti-sidetone network comprising

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

suppresses the transmitted signal in the received signal.

Maximum compensation is obtained when the following

conditions are fulfilled:

RSLPE × Rast1 = ZSET × (Rast2 + Rast3)

k = --(--R-----a--s--t--2(--R--×---a--s-(--tR-1----a×--s--t-R-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 chosen for 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 UBA1707 (see Fig.18)

attenuates the receiving signal from the line by 38 dB

before it enters the receiving amplifier. 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 “Applications

Handbook for Wired Telecom Systems, IC03b”.

handbook, full pagewidth

1999 Feb 17

LN

Zline

GND

ZSET

Rast1

RSLPE

Im

RXI

ZRXI

Rast2

Rast3

SLPE

Zbal

MGL216

Fig.10 Equivalent circuit of UBA1707 anti-sidetone bridge.

12

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