TS616IDW datasheet(33/36 Pages) STMICROELECTRONICS

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TS616

Increasing the line level using active impedance matching

33/36

Figure 70.

Equivalent schematic - Ro is the synthesized impedance

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 be 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 6.

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

Vi.Gi

Iout

1/2

kVoRL

2Rs1

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

---RL

--------

2Rs

-----------

–

2Rs

-----------

–

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

2R2

--------

–

⎝⎠

⎛⎞ GL 1

–

--------

–

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

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