MT91600
Step 2: Impedance Matching (R11, R18, R19, C8)
a)
Z
o
/ ( R1+R2) = kZ
o
/ R11
600/(220+220) = (k*600)/R11
let k = 125
∴
R11 = 55kΩ.
b)
In general,
kZ
o
= Z
LZ
where:
Z
LZ
= R18, for a resistive load.
Z
LZ
= [R18 + (R19 // C8)], for a complex load.
Since we are dealing with a resistive load in this example Z
LZ
= R18, and therefore:
kZ
o
= R18
(125 * 600)= R18
∴
R18 = 75kΩ.
Step 3: Network Balance Impedance (R16, R17)
R17 = [1.782 * Z
o
/ ( Z
o
+Z
NB
) * ( R13 / R12 )]
R17 + R16
[1 + R13 / R12)]
R17 = 0.4199
R17 + R16
set R17 = 100kΩ, R16 becomes 138kΩ.
∴
R16 = 138kΩ, R17 = 100kΩ.
Complex Line Impedance, Z
o
Data Sheet
In situations where the characteristic impedance of the line Z
o
is a complex value, determining the component
values for impedance matching (R11, R18, R19, C8) is as follows:
Given Z
o
= 220Ω + (820Ω // 120nF)
Z
o
/ ( R1+R2) = kZ
o
/ R11
where, kZ
o
= [R18 + (R19 // C8)]
Choose a standard value for C8 to find a suitable value for k.
Since 1nF exists, let C8 = 1nF then,
k = 120nF / C8
k = 120nF / 1nF
∴
k =120
R18 = k * 220Ω
R18 = 120 * 220Ω
R18 = 26400
R19 = k * 820Ω
R19 = 120 * 820
R19 = 98400
∴
R18 = 26k4Ω, R19 = 98k4Ω
(Equation 1)
8
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