DEMO-HSMS285-0 Datasheet, PDF (7/13 Pages) Broadcom Corporation. – Surface Mount Zero Bias Schottky Detector Diodes

The most difficult part of the ­design of a detector circuit
is the input impedance matching ­ network. For very
broadband ­detectors, a shunt 60 Ω resistor will give good
input match, but at the expense of detection ­sensitivity.
When maximum sensitivity is ­ required over a narrow
band of frequencies, a reactive matching network
is optimum. Such net­works can be realized in either
lumped or distributed elements, depending upon fre-
quency, size constraints and cost limitations, but certain
general design ­ principals exist for all types.^[3] ­ Design
work begins with the RF impedance of the HSMS-285x
­series, which is given in Figure 9.
FREQUENCY (GHz): 0.9-0.93
Figure 11. Input Impedance.
0.2 0.6
1
6
2
5
1 GHz
2
3
4
5
Figure 9. RF Impedance of the HSMS‑285x Series at-40 dBm.
The inpHuStMmS-a2t8c5hA,/6eAxfpigr1e5ssed in terms of return loss, is
given in Figure 12.
0
-5
-10
-15
915 MHz Detector Circuit
HSMS-285A/6A fig 13
Figure 10 illustrates a simple ­ impedance matching
-20
0.9
0.915
0.93
FREQUENCY (GHz)
network for a 915 MHz detector.
Figure 12. Input Return Loss.
RF
INPUT
65nH
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As can be s_He_Se_Mn_S,_-2t₈h₅e_A/6b_Aa_fn_igd₁₆over which a good match is
achieved is more than adequate for 915 MHz RFID ap-
plications.
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 10. 915 MHz Matching Network for the HSMS-285x Series at Zero Bias.
Voltage Doublers
To this point, we have restricted our discus­sion to single
diode ­ detectors. A glance at Figure 8, however, will lead
to the suggestion that the two types of single diode de-
tectors be combined into a two diode voltage doubler^[4]
(known also as a full wave rectifier). Such a detector is
shown in Figure 13.
A 65 nH inductor rotates the ­impedance of the diode to
a point on th_He_SMS_Sm_-28it₅h_A/6C_Ah_fia_gr₁t₄ where a shunt inductor can
pull it up to the ­center. The short length of 0.065" wide
RF IN
Z-MATCH
NETWORK
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 ^{Figure 13. Voltage Doubler Circuit.}
generated in the diode. The impedance of this circuit is
given in Figure 11.
HSMS-285X fig 11 was 7
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[2] _{Avago Application Note 969, An Optimum Zero Bias Schottky Detector Diode.}
[3] _{Avago Application Note 963, Impedance Matching Techniques for Mixers}
and Detectors.