HSMS-2850-TR1 Avago Technologies US Inc., HSMS-2850-TR1 Datasheet - Page 7

• Manufacturer Part Number: HSMS-2850-TR1
• Description: DETECTOR DIODE,1MHZ F(TEST),SOT-23
• Manufacturer: Avago Technologies US Inc.

Specifications of HSMS-2850-TR1

• Rohs Compliant: NO
• Diode Type: Schottky - Single
• Voltage - Peak Reverse (max): 2V
• Capacitance @ Vr, F: 0.3pF @ 1V, 1MHz
• Package / Case: SOT-23-3, TO-236-3, Micro3™, SSD3, SST3
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Max: -
• Power Dissipation (max): -
• Resistance @ If, F: -
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Since no external bias is used
with the HSMS-285x series, a
single transfer curve at any given
frequency is obtained, as shown in
Figure 2.
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 net-
works can be realized in either
lumped or distributed elements,
depending upon frequency, size
constraints and cost limitations,
but certain general design
principals exist for all types.
Design work begins with the RF
impedance of the HSMS-285x
series, which is given in Figure 9.
Figure 9. RF Impedance of the
HSMS-285x Series at -40 dBm.
915 MHz Detector Circuit
Figure 10 illustrates a simple
impedance matching network for
a 915 MHz detector.
[3]
[4]
[5]
0.2
Agilent Application Note 963, Impedance Matching Techniques for Mixers and Detectors.
Agilent Application Note 956-4, Schottky Diode Voltage Doubler.
Agilent Application Note 965-3, Flicker Noise in Schottky Diodes.
0.6
6
1
2
5
5
4
[3]
3
2
1 GHz
Figure 10. 915 MHz Matching
Network for the HSMS-285x Series
at Zero 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
center. The short 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
simultaneously provides the
return circuit for the current gen-
erated in the diode. The imped-
ance of this circuit is given in
Figure 11.
Figure 11. Input Impedance.
The input match, expressed in
terms of return loss, is given in
Figure 12.
INPUT
RF
FREQUENCY (GHz): 0.9-0.93
65nH
TRANSMISSION LINE
DIMENSIONS ARE FOR
MICROSTRIP ON
0.032" THICK FR-4.
WIDTH = 0.015"
LENGTH = 0.600"
WIDTH = 0.050"
LENGTH = 0.065"
100 pF
VIDEO
OUT
Figure 12. Input Return Loss.
As can be seen, the band over
which a good match is achieved is
more than adequate for 915 MHz
RFID applications.
Voltage Doublers
To this point, we have restricted
our discussion to single diode
detectors. A glance at Figure 8,
however, will lead to the sugges-
tion that the two types of single
diode detectors be combined into
a two diode voltage doubler
(known also as a full wave recti-
fier). Such a detector is shown in
Figure 13.
Figure 13. Voltage Doubler Circuit.
Such a circuit offers several
advantages. First the voltage
outputs of two diodes are added
in series, increasing the overall
value of voltage sensitivity for the
network (compared to a single
diode detector). Second, the RF
impedances of the two diodes are
added in parallel, making the job
of reactive matching a bit easier.
RF IN
-10
-15
-20
-5
0
7
0.9
NETWORK
Z-MATCH
FREQUENCY (GHz)
0.915
VIDEO OUT
[4]
0.93