Two SMA connectors (E.F. Johnson 142‑0701‑631 or
equivalent), a high‑Q capacitor (ATC 100A101MCA50 or
equivalent), miscellaneous hardware and an HSMS‑286B
are added to create the test circuit shown in Figure 16.
The calculated input impedance for this network is
shown in Figure 17.
2.45 GHz
FREQUENCY (GHz): 2.3-2.6
Figure 19. Input Impedance. Modified 2.45 GHz Circuit.
This does indeed result in a very good match at midband,
as shown in
HSMS-0005 fig 23 was 20
Figure 20.
0
FREQUENCY (GHz): 2.3-2.6
Figure 17. Input Impedance, 3 µA Bias.
The corresponding input match is shown in Figure 18. As
was the case with the lower frequency design, bandwidth
HSMS-0005 fig 21 was 18
is more than adequate for the intended RFID application.
0
RETURN LOSS (dB)
-5
-10
-15
RETURN LOSS (dB)
-5
-20
2.3
2.45
FREQUENCY (GHz)
2.6
-10
Figure 20. Input Return Loss. Modified 2.45 GHz Circuit.
-15
-20
2.3
2.45
FREQUENCY (GHz)
2.6
Figure 18. Input Return Loss, 3 µA Bias.
However, bandwidth is narrower and the designer runs
the risk of a shift in the midband frequency of his circuit
HSMS-285X fig 24 was 21
if there is any small deviation in circuit board or diode
characteristics due to lot‑to‑lot variation or change in
temper‑ature. The matching technique illustrated in
Figure 17 is much less sensitive to changes in diode and
circuit board processing.
A word of caution to the designer is in order. A glance
HSMS-285X
the fact
at Figure 17 will reveal
fig 22 was 19
that the circuit does
not provide the optimum impedance to the diode at
2.45 GHz. The temptation will be to adjust the circuit
elements to achieve an ideal single frequency match, as
illustrated in Figure 19.
5.8 GHz Detector Circuit
A possible design for a 5.8 GHz detector is given in Figure
21.
RF
INPUT
WIDTH = 0.016"
LENGTH = 0.037"
WIDTH = 0.045"
LENGTH = 0.073"
TRANSMISSION LINE
DIMENSIONS ARE FOR
Figure 21. 5.8 GHz Matching Network for the HSMS-286x Series at 3 µA Bias.
MICROSTRIP ON
0.032" THICK FR-4.
VIDEO
OUT
20 pF
9
AVAGO [ AVAGO TECHNOLOGIES LIMITED ]
