micrf213 Micrel Semiconductor, micrf213 Datasheet - Page 9

• Manufacturer Part Number: micrf213
• Description: Micrf213 3.3v, Qwikradio 315mhz Receiver
• Manufacturer: Micrel Semiconductor

Please keep in mind that these suggested values may
be different if the layout is not exactly the same as the
one depicted here.
For the frequency of 315MHz, the input impedance is
Z = 32.5 – j235Ω, then the matching components are
calculated by:
Equivalent parallel = B = 1/Z = 0.577 + j4.175
msiemens
Rp = 1 / Re (B);
Rp = 1.733 kΩ;
Q = SQRT (Rp/50 + 1)
Q = 5.972
Xm = Rp / Q
Xm = 290.21 Ω
Resonance Method For L-shape Matching Network
Lc = Xp / (2.Pi.f);
L2 = (Lc.Lp) / (Lc + Lp);
L2 = 66.3nH
C3 = 1.74pF
Doing the same calculation example with the Smith
Chart, it would appear as follows,
First, we plot the input impedance of the device,
(Z = 32.5 – j235)Ω @ 315MHz.(Figure 4).
Micrel, Inc.
May 2007
Freq (MHz)
303.825
315
345
Figure 4. Device’s Input Impedance, Z = 32.5 – j235 Ω
Table 4. Matching Values for the
Most Used Frequencies
C3 (pF)
1.8
1.8
1.8
L2 (nH)
72
68
56
Xp = 1 / Im (B)
Xp = 239.5 Ω
Lp = Xm / (2.Pi.f)
C3 = 1 / (2.Pi.f.Xm)
Z device (Ω)
34.6– j245.1
32.5 – j235
25.3 – j214
9
Second, we plot the shunt inductor (68nH) and the
series capacitor (1.8pF) for the desired input
impedance (Figure 5). We can see the matching
leading to the center of the Smith Chart or close to
50Ω.
Crystal Y1 or Y1A (SMT or leaded respectively) is the
reference clock for all the device internal circuits.
Desired
capacitance, 30ppm, ESR < 50Ω and a -40ºC to
+105ºC temperature range. Table 5 shows the crystal
frequencies and one of Micrel’s approved crystal
manufactures (www.hib.com.br).
The oscillator of the MICRF213 is a Colpitts type. It is
very sensitive to stray capacitance loads. Thus, very
good care must be taken when laying out the printed
circuit board. Avoid long traces and ground plane on
Figure 5. Plotting the Shunt Inductor
crystal
and Series Capacitor
characteristics
are:
M9999-052307-A
[phone]
10pF
MICRF213
load