TS615IPWT datasheet(34/36 Pages) STMICROELECTRONICS

34 / 36 page

TS615

Increasing the Line Level Using Active Impedance Matching

34/36

Let us write Vo°=kVo, where k is the matching factor varying between 1 and 2. If we assume that the

current through R3 is negligible, we can calculate the output resistance, Ro:

After choosing the k factor, Rs will equal to 1/2RL(k-1).

For a good impedance matching we assume that:

Equation 10

From Equation 9 and Equation 10, we derive:

Equation 11

By fixing an arbitrary value of R2, Equation 11 becomes:

Finally, the values of R2 and R3 allow us to extract R1 from Equation 6, so that:

Equation 12

with GL the required gain.

Table 7.

Components calculation for impedance matching implementation

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)

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

R2 (=R4)

Arbitrarily fixed

R3 (=R5)

R2/(1-Rs/0.5RL)

0.5RL(k-1)

Load viewed by each

driver

kRL/2

kV oRL

2R s1

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

---RL

--------1

2Rs

-----------

–

2Rs

-----------

–

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

2R2

--------

–



 GL 1

–

--------

–

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

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