TEA7092 datasheet(18/57 Pages) STMICROELECTRONICS

18 / 57 page

II - SPEECH FEATURES (continued)

II.2 - Impedance

TEA7092

SLPE

AGND

R11a

R11b

RECIN

SNLL

SNSL

C27

C12

R10

LDC

LAC

R29

ZASL

ZALL

R13

R27

Zimp =

LAC

LDC +ILAC

Figure 22 : TEA7092 Application Impedance

Allows the user to adjust the set impedance

by changing the value of R10, R9 and C9 ;

In this way the impedance can be adjusted

as a real one (only R10) or as a complex one

(R10, R9, C9).

ZALL

ZALS

Sidetone networks which are in parallel with

ZT, if the ratio : R13/R11a>>1 and

R27/(R11a+R11b)>>1, ZALL and ZASL are

negligible for the impedance calculation.

ZIC

Is the internal impedance of TEA7092.

It includes the impedance of the transmit

path which is equivalent to a current source

in parallel with Cpc (3nF), the impedance of

all the other stages which are equivalent to

Rpc (15k

Ω) and the impedance of the shunt

regulator stage (AC/DC decoupling stage)

made on Pin 30 (VS).

TEA7092 application impedance is :

Zimp = ZT//ZIC//(ZALL + R11a + R11b)

//(ZASL + R11a)//CR1

As it will be describe in Section II.4, the sidetone

networks are equal to :

ZALL

R27

R11a

+ R11b

⋅ (ZT//CR1//ZLL)

ZASL

R13

R11a

⋅ (ZT//CR1//ZSL)

Where ZLL is the long line impedance, and ZSL is

the short line impedance.

If R27/(R11a+R11b) and R13/R11a are higher than

100 (R27 and R13 = 3.3k

Ω):

ZALL and ZASL >> ZT and : Zimp = ZT//ZIC//CR1

Figure 24 and the Table 1 give the TEA7092 appli-

cation characteristics at IL = 40mA.

Table 1 (RI

= 20 ⋅ log

[Zimp

+ 600]

[Zimp

− 600]

)

Frequency

(Hz)

Real

Part ()

Imaginary

Part ()

Module ()

Phase

(deg)

Return

Loss

[Rl] (dB)

200

550

556

21.7

300

573

577

24.2

800

604

605

34.6

1 000

606

607

38.8

1 500

608

-5

608

42.1

2 500

606

-28

607

-3

32.6

3 500

603

-43

605

-4

28.8

5 000

597

-67

601

-6

7 000

589

-94

596

-9

9 000

579

-119

591

-12

19.8

12 000

560

-154

581

-15

17.3

0.1

0.2 0.3

0.5

f (kHz)

L = 20mA

L = 100mA

Country Limit

Request

Figure 24 : Return Loss

Rslp

Lsh

Zsh =

R3 + (j x 2 x

π x f x R3 x R12 x C11)

Regulator Shunt

Impedance

Figure 23 : Zsh Impedance

TEA7092 - TELEPHONE SET INTEGRATED CIRCUIT

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