December 2006
9
MICRF102
MICRF102
Micrel
Design Examples
Complete reference designs including gerber les can be
downloaded from Micrels website at: www.micrel.com/prod-
uct-info/qwikradio.shtml.
Antenna Characteristics
In this design, the desired loop inductance value is determined
according to the table below.
Freq.
R
XL
Ind
Q
K
(MHz)     (&)
(&)
(nH)
(XL/R)
  300
1.7
84.5
44.8
39.72
0.83
  315
2.34     89.3
45.1
39.65
0.85
  390
3.2
161
47.4
52.00
0.90
  434
2.1
136
50.0
78.33
0.96
The reference design, shown in Figure 7, has an antenna
meeting this requirement.
Figure 7. Demo Board PCB.
Loop antennas are often considered highly directional. In
fact small loop antennas can achieve transmit patterns close
in performance to a Dipole antenna. The radiation pattern
below is the theoretical radiation pattern for the antenna, as
shown in Figure 8.
E-total, phi = 0?/DIV>
E-total, phi = 90?/DIV>
(180-phi) direction
phi direction
30.0
180.0
60.0
120.0
150.0
150.0
120.0
60.0
30.0
0.0
Figure 8. Polar Elevation Pattern at 315MHz.
The 0 degree plot is the radiation pattern in the plane of the
transmitter PCB, the 90 degree plot represents the plane
perpendicular to the PCB. Micrels evaluation of the perfor-
mance of the board in Figure 8 indicates an even more uniform
radiation pattern that the theoretical plot shown here.
Supply Bypassing
Supply bypassing consists of three capacitors; C3 = 4.7礔,
C4 = 0.1礔and C5 = 100pF
C4
0.1礔
16V
C5
100pF
50V
C3
4.7礔
16V
+5VTX
VDD
V
SS
MICRF102
2
3
PC
1
ASK   8
ANTP   7
ANTM   6
SB   5
REFOSC
4
Figure 9. Supply Bypassing
Example to Calculate C
S
and C
P
Antenna Inductance
Calculation
Length_mils = 2815
dmils = 70
k = 0.85
Length
Length_mils  25.4
1000
Length  71.501
=
?/DIV>
(
)
=
d
dmils
d
=
?/DIV>
(
)
=
25 4
1000
1 778
.
.
L   0.2  Length  ln
Length
d
1.6    10
k
L   44  10
9
9
=
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
=    ?/DIV>
Where Length and d are in mm and L is in H;
Where k is a constant dependent on PCB material, copper
thickness, etc.
MICRF102 Series Capacitor Calculation:
f = 315 ?10
6
L = 46 ?10
-9
C
VAR
= 5 ?10
-12
C
P
= 12 ?10
-12
C
f    L
C
T
T
=
?nbsp   ?nbsp  ?/DIV>
=
?/DIV>
1
4
2 587  10
2
2
12
??/DIV>
.
C
C
C
C
SERIES
T
V AR
SERIES
=
=
?/DIV>
1
1
1
8 2  10
12
.
MICRF102 Series Capacitor Calculation:
f = 433.92 ?10
6
L = 52 ?10
-9
C
VAR
= 5 ?10
-12
C
P
= 2.7 ?10
-12
C
f    L
C
T
T
=
?nbsp   ?nbsp  ?/DIV>
=
?/DIV>
1
4
2 587  10
2
2
12
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制造商:MICREL 制造商全稱:Micrel Semiconductor 功能描述:QwikRadio UHF ASK Transmitter |
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MICRF103YM |
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MICRF103YM TR |
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