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TA0313

STMicroelectronics Solutions for ADSL Line Interfaces

A good impedance matching assumes:

Equation 5

From Equation 3 and Equation 5 we derive:

Equation 6

By fixing an arbitrary value for R2 in Equation 6, we arrive at:

Finally, the values of R2 and R3 allow us to extract R1 from Equation 1 so that:

Equation 7

Capabilities

The table below shows the calculated components for different values of k for a differential load of 25

Ω.

In all cases, R2=1000

Ω and the gain=16dB. The last column displays the maximum amplitude level on

the line regarding the TS613 maximum output capabilities (18Vp-p diff.) and a 1:2 line transformer ratio.

Measurement of power consumption in application

Conditions:

R1

R2 (=R4)

Arbitrarily fixed

R3 (=R5)

R2/(1-Rs/0.5RL)

Rs

0.5RL(k-1)

Active matching

k

R1

(

Ω)

R3

(

Ω)

Rs

(

Ω)

TS613 Output Level to get

12.4Vpp on the line with a

turn ratio of 2.

(Vp-p diff)

Maximum Line Level

(Vp-p diff)

1.3

953

1400

3.75 (3.9//100)

8.06

27.5

1.4

590

1620

5 (10//10)

8.68

25.7

1.5

422

2000

6.36 (6.8//100)

9.35

25.3

1.6

316

2490

7.57 (8.2//100)

9.95

23.7

1.7

261

3300

8.71 (10//68)

10.52

22.3

Passive matching

12.4

18

Ro

1

2

--- RL

=

R2

R3

-------

1

2Rs

RL

-----------

–

=

R3

R2

1

2Rs

RL

-----------

–

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

=

R 1

2R2

21

R2

R3

-------

–



 G

L

1

–

R2

R3

-------

–

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

=