TEA1069 datasheet(13/44 Pages) PHILIPS

13 / 44 page

1998 Jan 08

Philips Semiconductors

Product speciﬁcation

Versatile speech/dialler/ringer with

music-on-hold

TEA1069; TEA1069A

SIDETONE SUPPRESSION

Suppression of the transmitted signal in the earpiece is

obtained by the anti-sidetone network comprising R1//Zline,

R2, R3, R8, R9 and Zbal (see Fig.10). The maximum

compensation is obtained when the following conditions

are fulfilled:

(1)

(2)

(3)

The scale factor k is chosen to meet the compatibility with

a standard capacitor from the E6 or E12 series for Zline.

In practice, Zline varies considerably with the line type and

length. Therefore, the value chosen for Zbal should be for

an average line length thus giving optimum setting for

short or long lines.

Example: the balance impedance Zbal at which the

optimum suppression is present can be calculated as

()

kR3

()

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

bal

line

follows:

suppose Zline = 210 Ω + (1265 Ω//140 nF) representing a

5 km line of 0.5 mm diameter, copper, twisted-pair cable

matched to 600

Ω (176 Ω/km; 38 nF/km).

When k = 0.64 then R8 = 390

Ω;

Zbal = 130 Ω + (820 Ω//220 nF).

The anti-sidetone network for the TEA1069 and

TEA1069A shown in Fig.10 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. Figure 11 shows a conventional

Wheatstone bridge anti-sidetone circuit that can be used

as an alternative. Both bridge types can be used with

either resistive or complex set impedances. More

information on the balancing of anti-sidetone bridges can

be found in our publication

“Applications Handbook for

Wired telecom systems, IC03b”, order number

9397 750 00811.

Fig.10 Equivalent circuit of TEA1069 and TEA1069A anti-sidetone bridge.

handbook, full pagewidth

MSA500 - 1

SLPE

Zline

VEE

Zbal

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