MICRF211AYQS View Datasheet(PDF) - Micrel

Part Name

Description

MFG CO.

MICRF211AYQS

3V, QwikRadio® 433.92 MHz Receiver

Micrel 

Micrel

Freq (MHz)

390.0

418.0

433.92

C3 (pF)

1.5

1.5

1.5

L2(nH)

47

43

39

Z device (Ω)

22.5 – j198.5

21.4 – j186.1

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 – j174.2Ω, 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 = 1.65kΩ; Xp = 176.2Ω

Q = SQRT (Rp/50 + 1)

Q = 5.831

Xm = Rp / Q

Xm = 282.98Ω

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).

MICRF211

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

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

50Ω.

March 2007

Figure 5. Plotting the Shunt Inductor and Series

Capacitor.

9

M9999-030107

(408) 944-0800

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