MICRF213 Ver la hoja de datos (PDF) - Micrel
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MICRF213 Datasheet PDF : 16 Pages
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Micrel, Inc.
MICRF213
Application Information
ANT1
Helical PCB Antenna Pattern
C9
ANT2
L3
75nH 2%
J2
(np)SMA
C3
1.8pF
L1
39nH 5%
C8
6.8pF
+3.3V
L2
68nH 5%
C5
0.1µF
JP3
open
Y1
9.81563MHz
JP1
short
U1 MICRFAYQS
1 RO1
RO2 16
2 GNDRF
NC 15
3 ANT
RSSI 14
4 GNDRF
CAGC 13
5 VDD
CTH 12
6 SQ
SEL1 11
7 SEL0
DO 10
8 SHDN
GND 9
R3
RSSI
DO
+3.3V 1
GND 2
D0 3
NC 4
SH 5
RSSI 6
+3.3V
DO
SH
RSSI
JR2
short
+3.3V
R1
(np)
C6
C4
R2
0.47µF 4.7µF (np)
Figure 3. QR213HE1 Application Example, 315MHz
The MICRF213 can be fully tested by using one of the
many evaluation boards designed by Micrel and
intended for use with this device. As an entry level,
the QR213HE1 (reference Figure 3) offers a good
start for most applications. It has a helical PCB
antenna with its matching network, a band-pass-filter
front-end as a pre-selector filter, matching network
and the minimum components required to make the
device work. The minimum components are a crystal,
Cagc, and Cth capacitors. By removing the matching
network of the helical PCB antenna (C9 and L3), a
whip antenna (ANT2) or a RF connector (J2) can be
used instead. Figure 3 shows the entire schematic for
315MHz. Other frequencies can be used and the
values needed are listed in the tables below.
Capacitor C9 and inductor L3 are the passive
elements for the helical PCB matching network. It is
recommended that a tight tolerance be used for these
devices; such as 2% for the inductor and 0.1pF for the
capacitor. PCB variations may require different values
and optimization. Table 2 shows the matching
elements for the device frequency range. For
additional information, reference the: Small PCB
Antennas for Micrel RF Products application note.
Freq (MHz)
303.825
315
345
C9 (pF)
1.2
1.2
1.2
L3 (nH)
82
75
62
Table 2. Matching Values for the Helical PCB Antenna
To use another antenna, such as the whip kind, remove
C9 and place the whip antenna in the hole provided in
the PCB. Also, a RF signal can be injected there.
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
f = 1/(2*PI*(SQRT(L1*C8)). Table 3 shows the most
used frequency values.
Freq (MHz)
303.825
315
345
C8 (pF)
6.8
6.8
5.6
L1 (nH)
39
39
39
Table 3. Band-Pass-Filter Front-End Values
There is no need for the band-pass-filter front-end for
applications where it is proven the outside band noise
does not cause a problem. The MICRF213 has image
reject mixers which improve significantly the selectivity
and rejection of outside band noise.
Capacitor C3 and inductor L2 form the L-shape
matching network. The capacitor provides additional
attenuation for low frequency outside band noise and
the inductor provides additional ESD protection for the
antenna pin. Two ways can be used to find these
values, which are matched close to 50Ω. One method
is done by calculating the values using the equations
below and another by using a Smith chart. The latter
is made easier by using software that plots the values
of the components C8 and L1, like WinSmith by Noble
Publishing.
To calculate the matching values, one needs to know
the input impedance of the device. Table 4 shows the
input impedance of the MICRF213 and the suggested
matching values used for the most frequencies.
May 2007
8
M9999-052307-A
(408) 944-0800
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