Micrel MICRF010
June 2005
11
M9999-063005
(408) 955-1690
Additional Applications Information
In addition to the basic operation of the MICRF010, the
following enhancements can be made. In particular, it is
strongly recommended that the antenna impedance is
matched to the input of the IC.
Antenna Impedance Matching
Figure 7. Antenna Pin Input Impedance
Figure 7 and Table 2 presents the antenna pin input
impedance. The Antenna pin can be matched to 50Ω with
a high pass circuit as shown in Figure 8. That is, a shunt
inductor from the ANT Pin to ground and a series capacitor
from ANT Pin to the antenna.
Figure 8. Antenna with Matching Network to ANT Pin
Inductor values may be different from Table 2, depending
on PCB material, PCB thickness, ground configuration, and
how long the traces are in the layout. Values shown were
characterized for a 0.031 inch thickness, FR4 board, solid
ground plane on bottom layer, and very short traces.
MuRata and Coilcraft wire-wound 0603 or 0805 surface
mount inductors were tested, however, any wire-wound
inductor with high SRF (self-resonance frequency) should
do the job.
Frequency
(Mhz)
S11
Mag, angle
Z11, ohms C3, pF L2, nH
300 0.944,-36.65 14.45-j150 2.2 47
305 0.940,-37.499 14.84-j145 2.2 47
310 0.942,-37.579 14.28-j145 2.2 47
315 0.945, -37.66 13.48-j145 2.2 47
320 0.943,-38.237 13.58-j143 2 47
325 0.942, -38.814 13.43-j140 1.8 47
330 0.94, -39.39 13.5-j138 1.8 47
335 0.938, -39.967 13.59-j136 1.8 43
340 0.937, -40.544 13.44-j134 1.8 43
345 0.935, -41.12 13.51-j132 1.8 43
350 0.933, -41.697 13.57-j130 2 39
355 0.931, -42.274 13.62-j123 2.2 36
360 0.93, 42.85 13.48-j126 2.2 36
365 0.928, -43.427 13.52-j124 2 36
370 0.926, -44.004 13.57-j122 1.8 36
375 0.925, -44.581 13.42-j120 2.2 33
380 0.923, -45.157 13.46-j118 2 33
385 0.921, -45.734 13.49-j117 1.8 33
390 0.92, -46.311 13.35-j115 1.8 33
395 0.917, -46.729 13.6-j114 1.8 33
400 0.914, -47.148 13.89-j113 2 30
405 0.912, -47.566 14.00-j112 1.8 30
410 0.909, -47.985 14.25-j110 1.8 30
415 0.907, -48.403 14.34-j109 2.2 27
420 0.906, -48.797 14.28-j108 2 27
425 0.909, -49.152 13.63-j107 2 27
430 0.911, -49.507 13.15-j107 1.8 27
435 0.911, -49.925 12.94-j106 1.8 27
440 0.904, -50.571 13.66-j104 1.8 27
L2
C3
ANT Pin
Table 2
Shutdown Function
Duty-cycled operation of the MICRF010 (often referred to
as polling) is achieved by turning the MICRF010 on and off
via the SHUT pin. The shutdown function is controlled by a
logic state applied to the SHUT pin. When VSHUT is high,
the device goes into low-power standby mode. This pin is
pulled high internally, and it must be externally pulled low
to enable the receiver.
