UBA1707TS datasheet(12/36 Pages) PHILIPS

12 / 36 page

1999 Feb 17

Philips Semiconductors

Product speciﬁcation

Cordless telephone, answering machine

line interface

UBA1707

Fig.9 Receive amplifier.

handbook, full pagewidth

MGK711

RXM

2Vd

from AGC

RXI

RXO

UBA1707

Bit names are given in italics.

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)

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.

ast2

ast3

SLPE

()

ast1

SLPE

()

--------------------------------------------------------------------

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

MGL216

ZRXI

RXI

Rast1

Rast3

Rast2

SLPE

RSLPE

GND

Zline

ZSET

Zbal

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

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