MICRF218_11 MICREL [Micrel Semiconductor], MICRF218_11 Datasheet - Page 14

• Manufacturer Part Number: MICRF218_11
• Description: 3.3V, 315/433MHz Wide-IF Bandwidth ASK Receiver
• Manufacturer: MICREL [Micrel Semiconductor]

November 2011
Application Information
The MICRF218 can be fully tested by using one of
many evaluation boards designed at Micrel for this
device. As simple demonstrator, the QR218HE1
(Figure 7) offers a good start for most applications. It
has a helical PCB antenna with its matching network,
a bandpass-filter front-end as a pre-selector filter,
matching network and the minimum components
required to make the device work, which are a crystal,
Cagc, and Cth capacitors.
The matching network of the helical PCB antenna (C9
and L3) can be removed and a whip antenna (ANT2)
or a RF connector (J2) can be used instead. Figure 7
shows the entire schematic of it for 433.92MHz. Other
frequencies can be used. Matching network values
for other frequencies are listed in the tables below.
Capacitor C9 and inductor L3 are the passive
elements for the helical PCB matching network. Tight
tolerance is recommended for these devices, like 2%
for the inductor and 0.1pF for the capacitor. PCB
variations may require different component values and
optimization. Table 2 shows the matching elements
for the device frequency range. For additional
information look for Small PCB Antennas for Micrel RF
Figure 7. QR218HE1 Application Example, 433.92 MHz, Narrow Band
14
Products application note.
If whip antenna is used, remove C9 and place the
whip antenna in the hole provided in the PCB. Also,
RF signal can be injected there (add RF connector).
L1 and C8 form the pass-band-filter front-end. Its
purpose is to attenuate undesired outside band noise
which reduces the receiver performance. It is
calculated by the parallel resonance equation:
Table 2. Matching Values for the Helical PCB Antenna
f
Freq (MHz)

433.92
(2
315.0
390.0
418.0
*

1
L1
*
C8)
C9 (pF)
1.2
1.2
1.2
1.5
[phone]
M9999-111111
L3(nH)
75
43
36
30