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TA0313

STMicroelectronics Solutions for ADSL Line Interfaces

STMicroelectronics 

TA0313

STMicroelectronics Solutions for ADSL Line Interfaces

A good impedance matching assumes:

Equation 5

R o = 1-- RL

2

From Equation 3 and Equation 5 we derive:

Equation 6

R-----2-- = 1 – 2----R-----s-

R3

RL

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

R3 = -------R-----2-------

1 – 2----R-----s-

RL

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

Equation 7

R 1 = -----------------------2----R-----2------------------------

2  1

–

RR-----23--

GL

–

1

–

R-----2--

R3

with GL the required gain.

GL (gain for the loaded system)

R1

R2 (=R4)

R3 (=R5)

Rs

GL is fixed for the application requirements

GL=Vo/Vi=0.5(1+2R2/R1+R2/R3)/(1-R2/R3)

2R2/[2(1-R2/R3)GL-1-R2/R3]

Arbitrarily fixed

R2/(1-Rs/0.5RL)

0.5RL(k-1)

Capabilities

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

In all cases, R2=1000Ω 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.

Active matching

k

R1

R3

(Ω)

(Ω)

TS613 Output Level to get

Rs

12.4Vpp on the line with a Maximum Line Level

(Ω)

turn ratio of 2.

(Vp-p diff)

(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

Measurement of power consumption in application

Conditions:

l Passive impedance matching

l Transformer turns ratio: 2

l Maximum level required on the line: 12.4Vpp

l Maximum output level of the driver: 12.4Vpp

8/9

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