TS616 datasheet(25/27 Pages) STMICROELECTRONICS

25 / 27 page

TS616

25/27

Component Calculation

Let us consider the equivalent circuit for a sin-

gle-ended configuration as shown in Figure 69.

Figure 69: Single ended equivalent circuit

Let us consider the unloaded system. Assuming

the currents through R1, R2 and R3

are respectively:

as Vo° equals Vo without load, the gain in this

case becomes :

The gain, for the loaded system will be (eq1):

As shown in Figure70, this system is an ideal gen-

erator with a synthesized impedance as the inter-

nal impedance of the system. From this, the out-

put voltage becomes:

with Ro the synthesized impedance and Iout the

output current. On the other hand Vo can be ex-

pressed as:

By identification of both equations (eq2) and

(eq3),

the

synthesized

impedance

is,

with

Rs1=Rs2=Rs:

Figure 70: Equivalent schematic. Ro is the

synthesized impedance.

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 negligible, (eq4) becomes the fol-

lowing :

After choosing the k factor, Rs will equal to

1/2RL(k-1).

A good impedance matching assumes:

(eq4) and (eq5) give :

By fixing an arbitrary value of R2, (eq6) becomes :

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

R1 from (eq1), and it becomes:

Rs1

-1

Vo°

-1

½ RL

½ R1

Rs1

-1

Vo°

-1

½ RL

½ R1

2Vi

---------

–

()

--------------------------- and

()

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

Vo noload

()

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

2R2

-----------

--------

–

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

Vo with load

()

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

---

2R2

-----------

--------

–

------------------------------------ eq1

()

ViG

()

RoIout

()

–

eq2

()

Vi 1

2R2

-----------

--------





--------

–

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

Rs1Iout

--------

–

----------------------- eq3

()

–

--------

–

----------------- eq4

()

Vi.Gi

Iout

1/2

kV oRL

2R s1

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

--- RL eq5

()

--------1

2Rs

----------- eq6

()

–

2Rs

-----------

–

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

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