TEA7092 datasheet(24/57 Pages) STMICROELECTRONICS

24 / 57 page

II - SPEECH FEATURES (continued)

0dB

kIL

kIL = 0 for I

L =ISL

kIL = 1 for I

L =ILL

1 - kIL

AGC

21 to 15dB

(Code +6dB

not activated)

+6dB Code

20 REOUT

ZAL = K x ZALL + (1 - K) x ZASL

RECIN

ITX

SNSL

SNLL

C12

ZASL

R5+R6//C5

R13

TEA7092

R11

0.6V

Figure 37

II.4.2 - One Sidetone Network Principle

Figure 37 gives the sidetone connection.

The sidetone is optimized if :

V1 - V2 = VRECIN(19) -VSNSL/SNLL(15/16) =0

ZAL

R27

R11

⋅ ZB

With ZB = ZT//CR1//ZL.

Figure 38 gives the sidetone efficiency versus the

line length.

In receive mode the signal V1-V2 is amplified

through the receive path.

The attenuationdue to the external components of

the sidetone stage is :

Gsid

− V2

R11

+ R27

R11

+ R27 + ZAL

If, R27 = K1 x R11 and K1 >> 1 :

Gsid

− V2

R11

+ ZB

Thesidetoneattenuationis proportionalto R11andZB.

II.4.3 - Line Tracking Sidetone Principle

Figure 39 gives the sidetone connection.

The sidetone are optimized if : V1 - V2 = 0

- On long line connection :

V1 - V2 = VRECIN (19) -VSNLL (16) =0

⇒ ZALL =

R27

R11a

+ R11b ⋅

ZBL

with ZBL = ZT//CR1//ZLL.

- On short line connection :

V1 - V2 = VRECIN (19) -VSNSL (15) =0

⇒ ZASL =

R13

R11a

⋅ ZBS

with ZBS = ZT//CR1//ZSL.

ZLL is the long line length impedance and ZSL is

the short line length impedance.

Figure 40 gives the sidetone efficiency versus the

line length for a one sidetone network principle and

a tracking sidetone network principle.

Vear

High

Low

01234

Line (Km)

Figure 38

TEA7092 - TELEPHONE SET INTEGRATED CIRCUIT

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