HSMS-286R Datasheet, PDF (8/18 Pages) Broadcom Corporation. – Surface Mount Microwave Schottky Detector Diodes

915 MHz Detector Circuit
Figure 11 illustrates a simple impedance matching network
for a 915 MHz detector.
RF
INPUT
65nH
VIDEO
OUT
WIDTH = 0.050"
LENGTH = 0.065"
WIDTH = 0.015"
LENGTH = 0.600"
100 pF
TRANSMISSION LINE
DIMENSIONS ARE FOR
MICROSTRIP ON
0.032" THICK FR-4.
Figure 11. 915 MHz Matching Network for the HSMS-286x Series at 3 µA Bias.
A 65 nH inductor rotates the impedance of the diode to
a point on the Smith Chart where a shunt inductor can
pull it up to the c^He^Sn^Mt^Se^-2r⁸.⁵T^Ah^/6Ae^fis^gh¹o⁴ rt length of 0.065” wide
microstrip line is used to mount the lead of the diode’s
SOT‑323 package. A shorted shunt stub of length <λ/4
provides the necessary shunt inductance and simul­
taneously provides the return circuit for the current
generated in the diode. The impedance of this circuit is
given in Figure 12.
The HSMS-282x family is a better choice for 915 MHz ap‑
plications—the foregoing discussion of a design using
the HSMS-286B is offered only to illustrate a design
approach for technique.
RF
INPUT
VIDEO
OUT
WIDTH = 0.017"
LENGTH = 0.436"
WIDTH = 0.078"
LENGTH = 0.165"
100 pF
TRANSMISSION LINE
DIMENSIONS ARE FOR
MICROSTRIP ON
0.032" THICK FR-4.
Figure 14. 2.45 GHz Matching Network.
0.094" THROUGH, 4 PLACES
FINISHED
BOARD
SIZE IS
1.00" X 1.00".
MATERIAL IS
1/32" FR-4
EPOXY/
FIBERGLASS,
1 OZ. COPPER
BOTH SIDES.
FREQUENCY (GHz): 0.9-0.93
Figure 12. Input Impedance.
The input match, expressed in terms of return loss, is
given in FiguHreSM1S3-.285A/6A fig 15
0
-5
0.030" PLATED THROUGH HOLE,
3 PLACES
Figure 15. Physical Realization.
2.45 GHz Detector Circuit
HSMS-2860 fig 15
At 2.45 GHz, the RF impedance is closer to the line of
constant susceptance which passes through the center
of the chart, resulting in a design which is realized
entirely in distributed elements — see Figure 14.
In order to save cost (at the expense of having a larger
circuit), an open circuit shunt stub could be substituted
for the chip capacitor. On the other hand, if space is at a
premium, the long series transmission line at the input
to the diode can be replaced with a lumped inductor. A
possible physical realization of such a network is shown
in Figure 15, a demo board is available from Avago.
HSMS-2860
-10
RF IN
VIDEO OUT
-15
-20
0.9
0.915
0.93
FREQUENCY (GHz)
Figure 13. Input Return Loss.
As can be seen, the band over which a good match is
achieved is more^HSt^Mh^Sa^-n²⁸⁵a^Ad^/6e^Aq^fu^iga¹t⁶e for 915 MHz RFID ap‑
plications.
CHIP CAPACITOR, 20 TO 100 pF
Figure 16. Test Detector.
HSMS-285X fig 20 was 17
8