TA0313 Datasheet, PDF (8/9 Pages) STMicroelectronics – STMicroelectronics Solutions for ADSL Line Interfaces

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--}
G_L
–
1
–
R_-----2--
R3
with G_L the required gain.
G_L (gain for the loaded system)
R1
R2 (=R4)
R3 (=R5)
Rs
G_L is fixed for the application requirements
G_L=Vo/Vi=0.5(1+2R2/R1+R2/R3)/(1-R2/R3)
2R2/[2(1-R2/R3)G_L-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
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