AN1281

3/3

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By identification of both equations (2) and (3), the

synthesized impedance is, with Rs1=Rs2=Rs:

Unlike the level Vo° required for a passive imped-

ance, Vo° will be smaller than 2Vo in our case. Let

us write Vo°=kVo with k the matching factor vary-

ing between 1 and 2. Assuming that the current

through R3 is negligeable, it comes the following

resistance divider:

After choosing the k factor, Rs will equal to

1/2RL(k-1).

A good impedance matching assumes:

From (4) and (5) it becomes:

By fixing an arbitrary value for R2, (6) gives:

Finally, the values of R2 and R3 allow us to extract

R1 from (1), and it comes:

with GL the required gain.

CAPABILITIES

The table below shows the calculated compo-

nents

for different values of k. In this case

R2=1000

Ω and the gain=16dB. The last column

displays the maximum amplitude level on the line

regarding the TS613 maximum output capabilities

(18Vpp diff.) and a 1:2 line transformer ratio.

MEASUREMENT OF THE POWER

CONSUMPTION IN THE ADSL APPLICATION

Conditions:

Passive impedance matching

Transformer turns ratio: 2

Maximun level required on the line: 12.4Vpp

Maximum output level of the driver: 12.4Vpp

Crest factor: 5.3 (Vp/Vrms)

The TS613 power consumption during emission

on 900 and 4550 meter twisted pair telephone

lines: 360mW

Figure 5 : Equivalent schematic. Ro is the syn-

thesized impedance

Ro

Rs

1

R2

R3

-------

–

----------------- 4

()

,

=

Ro

Vi.Gi

Iout

1/2

RL

Ro

kVoRL

RL

2Rs1

+

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

=

Ro

1

2

---RL 5

()

,

=

R2

R3

-------

1

2Rs

RL

---------- 6

()

,

–

=

R3

R2

1

2Rs

RL

----------

–

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

=

R1

2R2

21

R2

R3

-------

–





GL

1

–

R2

R3

-------

–

--------------------------------------------------------- 7

()

,

=

GL (gain for the

loaded system)

GL is fixed for the application requirements

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

R1

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

R2 (=R4)

Abritrary 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

(Vpp diff)

Maximum

Line level

(Vpp diff)

1.3

820

1500

3.9

8

27.5

1.4

490

1600

5.1

8.7

25.7

1.5

360

2200

6.2

9.3

25.3

1.6

270

2400

7.5

9.9

23.7

1.7

240

3300

9.1

10.5

22.3

Passive matching

12.4

18