MICRF211 datasheet(9/18 Pages) MICREL

9 / 18 page

Micrel

MICRF211

March 2007

M9999-030107

(408) 944-0800

Freq (MHz)

C3 (pF)

L2(nH)

Z device (

Ω)

390.0

1.5

22.5 – j198.5

418.0

1.5

21.4 – j186.1

433.92

1.5

18.6 – j174.2

Table 4: matching values for the most used frequencies

For the frequency of 433.92MHz, the input impedance

is Z = 18.6 – j174.2

Ω, then the matching components

are calculated by,

Equivalent parallel = B = 1/Z = 0.606 + j5.68 msiemens

Rp = 1 / Re (B);

Xp = 1 / Im (B)

Rp = 1.65k

Ω;

Xp = 176.2

Ω

Q = SQRT (Rp/50 + 1)

Q = 5.831

Xm = Rp / Q

Xm = 282.98

Ω

Resonance Method For L-shape Matching Network

Lc = Xp / (2×Pi×f);

Lp = Xm / (2×Pi×f)

L2 = (Lc×Lp) / (Lc + Lp);

C3 = 1 / (2×Pi×f×Xm)

L2 = 39.8nH

C3 = 1.3pF

Doing the same calculation example with the Smith

Chart, it would appear as follows,

First, we plot the input impedance of the device,

(Z = 18.6 – j174.2)

Ω @ 433.92MHz.(Figure 4).

Figure 4: device’s input impedance, Z = 18.6 – j174.2

Ω

Second, we plot the shunt inductor (39nH) and the

series

capacitor

(1.5pF)

for

the

desired

input

impedance (Figure 5). We can see the matching

leading to the center of the Smith Chart or close to

Ω.

Figure 5. Plotting the Shunt Inductor and Series

Capacitor.

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