ETC HSMS-286ASERIES

Surface Mount Microwave
Schottky Detector Diodes in
SOT-323 (SC-70)
Technical Data
HSMS-285A Series
HSMS-286A Series
Features
• Surface Mount SOT-323
Package
• High Detection Sensitivity:
Up to 50 mV/µW at 915 MHz
Up to 35 mV/µW at 2.45 GHz
Up to 25 mV/µW at 5.80 GHz
• Low Flicker Noise:
-162 dBV/Hz at 100 Hz
Package Lead Code
Identification
(Top View)
Description
SINGLE
SERIES
B
COMMON
ANODE
C
COMMON
CATHODE
E
F
Hewlett-Packard’s HSMS-285A
family of zero bias Schottky detector
diodes and the HSMS-286A family of
DC biased detector diodes have been
designed and optimized for use from
915 MHz to 5.8 GHz. They are ideal
for RF/ID and RF Tag, cellular and
other consumer applications
requiring small and large signal
detection, modulation, RF to DC
conversion or voltage doubling.
• Low FIT (Failure in Time)
Rate*
• Tape and Reel Options
Available
* For more information see the
Surface Mount Schottky
Reliability Data Sheet.
DC Electrical Specifications, TC = +25°C, Single Diode
Part
Number
HSMS-
Package
Marking
Code[1]
Lead
Code
285B
285C
286B
286C
286E
286F
P0
P2
T0
T2
T3
T4
B
C
B
C
E
F
Configuration
Single [2]
Series Pair [2,3]
Single [4]
Series Pair [2,3]
Common Anode [2,3]
Common Cathode [2,3]
Test Conditions
Notes:
1. Package marking code is laser marked.
2. ∆VF for diodes in pairs is 15.0 mV maximum at 1.0 mA.
3. ∆CT for diodes in pairs is 0.05 pF maximum at -0.5 V.
Available in various package
configurations, these two families of
detector diodes provide low cost
solutions to a wide variety of design
problems. Hewlett-Packard’s
manufacturing techniques assure
that when two diodes are mounted
into a single SOT-323 package, they
are taken from adjacent sites on the
wafer, assuring the highest possible
degree of match.
Maximum Forward
Voltage VF
(mV)
Typical
Capacitance CT
(pF)
150
250
0.30
250
350
0.25
IF = 0.1 mA IF = 1.0 mA
VR = 0.5 V to -1.0 V
f = 1 MHz
2
RF Electrical Parameters, TC = +25oC, Single Diode
Part
Number
Typical Tangential Sensitivity Typical Voltage Sensitivity γ
TSS (dBm) @ f =
(mV/ µW) @ f =
HSMS-
915 MHz 2.45 GHz
285B
285C
Test
Conditions
286B
286C
286E
286F
Test
Conditions
-57
-56
5.8 GHz
-55
Typical Video
Resistance Rv (KΩ)
915 MHz 2.45 GHz 5.8 GHz
40
30
22
8.0
Video Bandwidth = 2 MHz
Zero Bias
-57
-56
-55
Power in = 40 dBm
RL = 100 LW, Zero Bias
50
35
25
5.0
Video Bandwidth = 2 MHz
I b = 5 µA
Power in = – 40 dBm
RL = 100 KΩ, I b = 5 µA
Absolute Maximum Ratings, Ta = 25ºC, Single Diode
Symbol
PIV
TJ
TSTG
TOP
θjc
Absolute Maximum[1]
HSMS-285x HSMS-286x
Peak Inverse Voltage
V
2.0
4.0
Junction Temperature
°C
150
150
Storage Temperature
°C
-65 to 150
-65 to 150
Operating Temperature
°C
-65 to 150
-65 to 150
[2]
Thermal Resistance
°C/W
150
150
Parameter
Unit
ESD WARNING: Handling
Precautions Should Be Taken
To Avoid Static Discharge.
Notes:
1. Operation in excess of any one of these conditions may result in
permanent damage to the device.
2. TC = +25°C, where TC is defined to be the temperature at the package pins where contact is made to the circuit board.
Equivalent Circuit Model
HSMS-285B, HSMS-286B
0.08 pF
Singles
Rj
2 nH
RS
0.18 pF
RS = series resistance (see Table of SPICE parameters)
Rj =
8.33 X 10-5 nT
Ib + Is
where
Ib = externally applied bias current in amps
Is = saturation current (see table of SPICE parameters)
T = temperature, °K
n = identity factor (see table of SPICE parameters)
SPICE Parameters
Parameter
BV
CJO
EG
IBV
IS
N
RS
PB (VJ)
PT (XTI)
M
Units
V
pF
eV
A
A
Ω
V
HSMS-285A
3.8
0.18
0.69
3 x 10E - 4
3 x 10E - 6
1.06
25
0.35
2
0.5
HSMS-286A
7.0
0.18
0.69
10E - 5
5 x 10E - 8
1.08
5.0
0.65
2
0.5
3
1
0.1
TA = +85°C
TA = +25°C
TA = –55°C
10
1
.1
.01
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
VF – FORWARD VOLTAGE (V)
10
5.8 GHz
5.8 GHz
1
0.3
-50
0
-10
-20
-40
-30
Figure 5. +25°C Expanded Output
Voltage vs. Input Power. See Figure 4.
3.1
40
2.9
OUTPUT VOLTAGE (mV)
35
30
25
20
Input Power =
–30 dBm @ 2.45 GHz
Data taken in fixed-tuned
FR4 circuit
10
.1
1
2.5
2.3
2.1
1.9
1.7
1.5
1.3
MEASUREMENTS MADE USING A
0.9
10
FREQUENCY = 2.45 GHz
PIN = -40 dBm
RL = 100 KΩ
1.1 FR4 MICROSTRIP CIRCUIT.
RL = 100 KΩ
5
2.7
100
BIAS CURRENT (µA)
Figure 7. Voltage Sensitivity as a
Function of DC Bias Current,
HSMS-286A.
10 µA
1000
5 µA
100
Frequency = 2.45 GHz
Fixed-tuned FR4 circuit
10
RL = 100 KΩ
DIODES TESTED IN FIXED-TUNED
FR4 MICROSTRIP CIRCUITS.
POWER IN (dBm)
Figure 4. +25°C Output Voltage vs.
Input Power, HSMS-285A Series at Zero
Bias, HSMS-286A Series at 3 µA Bias.
OUTPUT VOLTAGE (mV)
20 µA
2.45 GHz
DIODES TESTED IN FIXED-TUNED
FR4 MICROSTRIP CIRCUITS.
-30
1
0.25
10,000
10
POWER IN (dBm)
15
0.20
Figure 3. Forward Voltage Match,
HSMS-286C, E and F Pairs.
VOLTAGE OUT (mV)
VOLTAGE OUT (mV)
VOLTAGE OUT (mV)
915 MHz
-40
0.15
915 MHz
2.45 GHz
-50
0.10
RL = 100 KΩ
1000
0.3
∆VF (right scale)
FORWARD VOLTAGE (V)
30
RL = 100 KΩ
1
10
1
0.05
Figure 2. Forward Current vs. Forward
Voltage at Temperature, HSMS-286A
Series.
10000
10
IF (left scale)
FORWARD VOLTAGE (V)
Figure 1. +25°C Forward Current vs.
Forward Voltage, HSMS-285A Series.
100
FORWARD CURRENT (µA)
10
0.01
100
100
FORWARD CURRENT (mA)
IF – FORWARD CURRENT (mA)
100
FORWARD VOLTAGE DIFFERENCE (mV)
Typical Parameters, Single Diode
0 10 20 30 40 50 60 70 80 90 100
TEMPERATURE (°C)
Figure 8. Output Voltage vs.
Temperature, HSMS-285A Series.
1
–40
–30
–20
–10
0
10
POWER IN (dBm)
Figure 6. Dynamic Transfer
Characteristic as a Function of DC Bias,
HSMS-286A.
4
Applications Information
Introduction
Hewlett-Packard’s family of
HSMS-285A zero bias Schottky
diodes have been developed
specifically for low cost, high
volume detector applications
where bias current is not available.
The HSMS-286A family of DC
Schottky diodes have been
developed for low cost, high
volume detector applications
where stability over temperature is
an important design consideration.
Schottky Barrier Diode
Characteristics
Stripped of its package, a Schottky
barrier diode chip consists of a
metal-semiconductor barrier
formed by deposition of a metal
layer on a semiconductor. The
most common of several different
types, the passivated diode, is
shown in Figure 9, along with its
equivalent circuit.
8.33 X 10-5 n T
R j = –––––––––––– = R V – R s
IS + I b
0.026
= ––––– at 25°C
IS + I b
where
n = ideality factor (see table of
SPICE parameters)
T = temperature in °K
IS = saturation current (see
table of SPICE parameters)
Ib = externally applied bias
current in amps
IS is a function of diode barrier
height, and can range from
picoamps for high barrier diodes
to as much as 5 µA for very low
barrier diodes.
The Height of the Schottky
Barrier
The current-voltage characteristic
of a Schottky barrier diode at
room temperature is described by
the following equation:
(with high values of IS, suitable for
zero bias applications) are realized
on p-type silicon. Such diodes
suffer from higher values of RS
than do the n-type. Thus, p-type
diodes are generally reserved for
detector applications (where very
high values of RV swamp out high
RS) and n-type diodes are used for
mixer applications (where high
L.O. drive levels keep RV low).
Measuring Diode Parameters
The measurement of the five
elements which make up the
equivalent circuit for a packaged
Schottky diode (see Figure 10) is a
complex task. Various techniques
are used for each element. The
task begins with the elements of
the diode chip itself.
CP
LP
RV
RS
RS
METAL
PASSIVATION
N-TYPE OR P-TYPE EPI
V - IR
I = IS (exp ––––––S - 1)
0.026
(
PASSIVATION
LAYER
SCHOTTKY JUNCTION
Cj
Rj
N-TYPE OR P-TYPE SILICON SUBSTRATE
CROSS-SECTION OF SCHOTTKY
BARRIER DIODE CHIP
EQUIVALENT
CIRCUIT
Figure 9. Schottky Diode Chip.
RS is the parasitic series resistance
of the diode, the sum of the
bondwire and leadframe
resistance, the resistance of the
bulk layer of silicon, etc. RF
energy coupled into RS is lost as
heat — it does not contribute to
the rectified output of the diode.
CJ is parasitic junction capacitance
of the diode, controlled by the
thickness of the epitaxial layer and
the diameter of the Schottky
contact. R j is the junction
resistance of the diode, a function
of the total current flowing
through it.
)
On a semi-log plot (as shown in
the HP catalog) the current graph
will be a straight line with inverse
slope 2.3 X 0.026 = 0.060 volts per
cycle (until the effect of RS is seen
in a curve that droops at high
current). All Schottky diode curves
have the same slope, but not
necessarily the same value of
current for a given voltage. This is
determined by the saturation
current, IS, and is related to the
barrier height of the diode.
Through the choice of p-type or
n-type silicon, and the selection of
metal, one can tailor the
characteristics of a Schottky
diode. Barrier height will be
altered, and at the same time CJ
and RS will be changed. In general,
very low barrier height diodes
CJ
FOR THE HSMS-285A or HSMS-286A SERIES
CP = 0.08 pF
LP = 2 nH
CJ = 0.18 pF
RS = 25 Ω
RV = 9 KΩ
Figure 10. Equivalent Circuit of a
Schottky Diode.
RS is perhaps the easiest to
measure accurately. The V-I curve
is measured for the diode under
forward bias, and the slope of the
curve is taken at some relatively
high value of current (such as
5 mA). This slope is converted into
a resistance Rd.
0.026
RS = Rd – ––––––
If
RV and CJ are very difficult to
measure. Consider the impedance
of CJ = 0.16 pF when measured at
1 MHz — it is approximately 1 MΩ.
5
For a well designed zero bias
Schottky, RV is in the range of 5 to
25 KΩ, and it shorts out the
junction capacitance. Moving up to
a higher frequency enables the
measurement of the capacitance,
but it then shorts out the video
resistance. The best measurement
technique is to mount the diode in
series in a 50 Ω microstrip test
circuit and measure its insertion
loss at low power levels (around
-20 dBm) using an HP8753C
network analyzer. The resulting
display will appear as shown in
Figure 11.
-10
50 Ω
INSERTION LOSS (dB)
-15
0.16 pF
50 Ω
-20
-25
50 Ω 9 KΩ
-30
50 Ω
-35
-40
3
10
100
1000 3000
FREQUENCY (MHz)
Figure 11. Measuring CJ and R V.
linear analysis program having the
five element equivalent circuit
with RV, CJ and RS fixed. The
optimizer can then adjust the
values of LP and CP until the
calculated S11 matches the
measured values. Note that
extreme care must be taken to deembed the parasitics of the 50 Ω
test fixture.
Detector Circuits
When DC bias is available,
Schottky diode detector circuits
can be used to create low cost RF
and microwave receivers with a
sensitivity of -55 dBm to
-57 dBm.[1] Moreover, since
external DC bias sets the video
impedance of such circuits, they
display classic square law
response over a wide range of
input power levels[2,3]. These
circuits can take a variety of
forms, but in the most simple case
they appear as shown in Figure 12.
This is the basic detector circuit
used with the HSMS-286A family
of diodes.
At frequencies below 10 MHz, the
video resistance dominates the
loss and can easily be calculated
from it. At frequencies above 300
MHz, the junction capacitance sets
the loss, which plots out as a
straight line when frequency is
plotted on a log scale. Again,
calculation is straightforward.
Where DC bias is not available, a
zero bias Schottky diode is used to
replace the conventional Schottky
in these circuits, and bias choke L1
is eliminated. The circuit then is
reduced to a diode, an RF
impedance matching network and
(if required) a DC return choke
and a capacitor. This is the basic
detector circuit used with the
HSMS-285A family of diodes.
LP and CP are best measured on
the HP8753C, with the diode
terminating a 50 Ω line on the
input port. The resulting tabulation
of S11 can be put into a microwave
In the design of such detector
circuits, the starting point is the
equivalent circuit of the diode, as
shown in Figure 10.
[1]
Of interest in the design of the
video portion of the circuit is the
diode’s video impedance — the
other four elements of the equivalent circuit disappear at all
reasonable video frequencies. In
general, the lower the diode’s
video impedance, the better the
design.
DC BIAS
L1
RF
IN
Z-MATCH
NETWORK
VIDEO
OUT
DC BIAS
L1
RF
IN
Z-MATCH
NETWORK
VIDEO
OUT
Figure 12. Basic Detector
Circuits.
The situation is somewhat more
complicated in the design of the
RF impedance matching network,
which includes the package
inductance and capacitance
(which can be tuned out), the
series resistance, the junction
capacitance and the video
resistance. Of these five elements
of the diode’s equivalent circuit,
the four parasitics are constants
and the video resistance is a
function of the current flowing
through the diode.
Hewlett-Packard Application Note 923, Schottky Barrier Diode Video Detectors.
Hewlett-Packard Application Note 986, Square Law and Linear Detection.
[3] Hewlett-Packard Application Note 956-5, Dynamic Range Extension of Schottky Detectors.
[2]
6
26,000
RV ≈ ––––––
IS + Ib
where
IS = diode saturation current
in µA
Ib = bias current in µA
Saturation current is a function of
the diode’s design,[4] and it is a
constant at a given temperature.
For the HSMS-285A series, it is
typically 3 to 5 µA at 25°C. For the
medium barrier HSMS-2860 family,
saturation current at room
temperature is on the order of
50 nA.
constraints and cost limitations,
but certain general design
principals exist for all types.[5]
Design work begins with the RF
impedance of the HSMS-285A
series, which is given in Figure 13.
Note that the impedance of the
HSMS-286A series is very similar
when bias current is set to 3 µA.
2
0.2
0.6
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 generated in
the diode. The impedance of this
circuit is given in Figure 15.
5
1
1 GHz
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 networks can be realized in either
lumped or distributed elements,
depending upon frequency, size
[4]
[5]
3
4
5
6
FREQUENCY (GHz): 0.9-0.93
Figure 13. RF Impedance of the
HSMS-285A Series at -40 dBm.
915 MHz Detector Circuit
Figure 14 illustrates a simple
impedance matching network for a
915 MHz detector.
65nH
RF
INPUT
VIDEO
OUT
WIDTH = 0.050"
LENGTH = 0.065"
100 pF
WIDTH = 0.015"
LENGTH = 0.600"
TRANSMISSION LINE
DIMENSIONS ARE FOR
MICROSTRIP ON
0.032" THICK FR-4.
Figure 14. 915 MHz Matching
Network for the HSMS-285A
Series at Zero Bias or the
HSMS-286A 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
center. The short length of 0.065"
Figure 15. Input Impedance.
The input match, expressed in
terms of return loss, is given in
Figure 16.
0
RETURN LOSS (dB)
Together, saturation and (if used)
bias current set the detection
sensitivity, video resistance and
input RF impedance of the
Schottky detector diode. Since no
external bias is used with the
HSMS-285A series, a single
transfer curve at any given
frequency is obtained, as shown in
Figure 4. Where bias current is
used, some tradeoff in sensitivity
and square law dynamic range is
seen, as shown in Figure 6 and
described in reference [3].
-5
-10
-15
-20
0.9
0.915
0.93
FREQUENCY (GHz)
Figure 16. 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.
Hewlett-Packard Application Note 969, An Optimum Zero Bias Schottky Detector Diode.
Hewlett-Packard Application Note 963, Impedance Matching Techniques for Mixers and Detectors.
WIDTH = 0.017"
LENGTH = 0.436"
0.00 REF.
0.138
VIDEO
OUT
0.900
1.000
HSMS-285A
RF
INPUT
0.00 REF.
0.100
7
#2-56 TAP
0.40 MIN.,
4 PLACES
1.000
0.900
100 pF
WIDTH = 0.078"
LENGTH = 0.165"
0.670
TRANSMISSION LINE
DIMENSIONS ARE FOR
MICROSTRIP ON
0.032" THICK FR-4.
Figure 17. 2.45 GHz Matching
Network for the HSMS-285A
Series.
0.330
0.100
0.00 REF.
#2-56 TAP
THROUGH,
4 PLACES
0.00 REF.
MATERIAL:
0.250" H.H.
BRASS PLATE
Figure 19. Mounting Plate.
0.094" THROUGH, 4 PLACES
0.030" PLATED THROUGH HOLE,
3 PLACES
FREQUENCY (GHz): 2.3-2.6
Figure 21. Input Impedance.
HSMS-2850
0
RF IN
VIDEO OUT
H
CHIP CAPACITOR, 20 TO 100 pF
Figure 18. Physical Realization.
Figure 20. Test Detector.
2.45 GHz Detector Circuit
At 2.45 GHz, the RF impedance of
the HSMS-285A series 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 17.
Two SMA connectors (E.F.
Johnson 142-0701-631 or
equivalent), a high-Q capacitor
(ATC 100A101MCA50 or
equivalent), miscellaneous
hardware and an HSMS-285B are
added to create the test circuit
shown in Figure 20.
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 18.
This board is mounted on the
brass or aluminum mounting plate
shown in Figure 19.
The calculated input impedance
for this network is shown in
Figure 21.
The corresponding input match is
shown in Figure 22. As was the
case with the lower frequency
design, bandwidth is more than
adequate for the intended RFID
application. Note that this same
design applies to the HSMS-286A
series when it is used with 3 to
5 µA of external bias.
A word of caution to the designer
is in order. A glance at Figure 21
will reveal the fact that the circuit
does not provide the optimum
RETURN LOSS (dB)
H
FINISHED
BOARD
SIZE IS
1.00" X 1.00".
MATERIAL IS
1/32" FR-4
EPOXY/
FIBERGLASS,
1 OZ. COPPER
BOTH SIDES.
NOTE THAT
THE BACK SIDE
OF THE BOARD
IS A GROUND
PLANE.
-5
-10
-15
-20
2.3
2.45
2.6
FREQUENCY (GHz)
Figure 22. Input Return Loss.
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 23.
This does indeed result in a very
good match at midband, as shown
in Figure 24.
However, bandwidth is narrower
and the designer runs the risk of a
shift in the midband frequency of
his circuit if there is any small
deviation in circuit board or diode
characteristics due to lot-to-lot
variation or change in temperature. The matching technique
illustrated in Figure 21 is much
less sensitive to changes in diode
and circuit board processing.
8
5.8 GHz Detector Circuit
A possible design for a 5.8 GHz
detector is given in Figure 25.
HSMS-285A SERIES
VIDEO
OUT
RF
INPUT
WIDTH = 0.016"
LENGTH = 0.037"
20 pF
As was the case at 2.45 GHz, the
circuit is entirely distributed
element, both low cost and
compact. Input impedance for this
network is given in Figure 26.
WIDTH = 0.045"
LENGTH = 0.073"
TRANSMISSION LINE
DIMENSIONS ARE FOR
MICROSTRIP ON
0.032" THICK FR-4.
Figure 25. 5.8 GHz Matching
Network for the HSMS-285A
Series at Zero Bias or the
HSMS-286A Series at 3 µA Bias.
Input return loss, shown in
Figure 27, exhibits wideband
match.
Voltage Doublers
To this point, we have restricted
our discussion to single diode
detectors. A glance at Figure 12,
however, will lead to the
suggestion that the two types of
single diode detectors be
combined into a two diode voltage
doubler[6] (known also as a full
wave rectifier). Such a detector is
shown in Figure 28.
RF IN
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.
Such a circuit can easily be
realized using the two series
diodes in the HSMS-285C or the
HSMS-286C.
FREQUENCY (GHz): 2.3-2.6
FREQUENCY (GHz): 5.6-6.0
Figure 26. Input Impedance.
0
0
-5
-5
RETURN LOSS (dB)
RETURN LOSS (dB)
Figure 23. Input Impedance.
Modified 2.45 GHz Circuit.
-10
-15
2.45
FREQUENCY (GHz)
Figure 24. Input Return Loss.
Modified 2.45 GHz Circuit.
[6]
VIDEO OUT
Figure 28. Voltage Doubler
Circuit.
2.45 GHz
-20
2.3
Z-MATCH
NETWORK
2.6
-10
-15
-20
5.6
5.7
5.8
5.9
FREQUENCY (GHz)
Figure 27. Input Return Loss.
Hewlett-Packard Application Note 956-4, Schottky Diode Voltage Doubler.
6.0
The “Virtual Battery”
The voltage doubler can be used
as a virtual battery, to provide
power for the operation of an I.C.
or a transistor oscillator in a tag.
Illuminated by the CW signal from
a reader or interrogator, the
Schottky circuit will produce
power sufficient to operate an I.C.
or to charge up a capacitor for a
burst transmission from an
oscillator. Where such virtual
batteries are employed, the bulk,
cost, and limited lifetime of a
battery are eliminated.
9
NOISE TEMPERATURE RATIO (dB)
dBV/Hz
Thus, for a diode with RV = 9 KΩ,
the noise voltage is 12.2 nV/Hz or
-158 dBV/Hz. On the graph of
Figure 26, -158 dBV/Hz would
replace the zero on the vertical
scale to convert the chart to one of
absolute noise voltage vs.
frequency.
Temperature Compensation
The compression of the detector’s
transfer curve is beyond the scope
of this data sheet, but some
general comments can be made.
As was given earlier, the diode’s
video resistance is given by
10-5
8.33 X
nT
RV = ––––––––––––
IS + I b
where T is the diode’s temperature in °K.
As can be seen, temperature has a
strong effect upon RV, and this
will in turn affect video bandwidth
and input RF impedance. A glance
at Figure 7 suggests that the
proper choice of bias current in
the HSMS-286A series can minimize variation over temperature.
10
5
0
-5
10
20 log10 v
100
1000
10000
100000
FREQUENCY (Hz)
Figure 29. Typical Noise
Temperature Ratio.
Noise temperature ratio is the
quotient of the diode’s noise
power (expressed in dBV/Hz)
divided by the noise power of an
ideal resistor of resistance R = RV.
For an ideal resistor R, at 300°K,
the noise voltage can be computed
from
It should be noted that curves
such as those given in Figures 30
and 31 are highly dependent upon
the exact design of the input
impedance matching network.
The designer will have to experiment with bias current using his
specific design.
120
INPUT POWER = –30 dBm
3.0 µA
100
80
1.0 µA
10 µA
60
40
-55
0.5 µA
-35
-15
5
25
45
65
85
TEMPERATURE (°C)
Figure 30. Output Voltage vs.
Temperature and Bias Current in the
915 MHz Voltage Doubler using the
HSMS-286C.
35
The detector circuits described
earlier were tested over temperature. The 915 MHz voltage doubler
using the HSMS-286C series pair
produced the output voltages as
shown in Figure 30. The use of
3 µA of bias resulted in the highest
voltage sensitivity, but at the cost
of a wide variation over temperature. Dropping the bias to 1 µA
produced a detector with much
less temperature variation.
v = 1.287 X 10-10 √R volts/Hz
[7]
A similar experiment was conducted with the HSMS-286B in the
5.8 GHz detector. Once again,
reducing the bias to some level
under 3 µA stabilized the output of
the detector over a wide temperature range.
OUTPUT VOLTAGE (mV)
15
which can be expressed as
Hewlett-Packard Application Note 965-3, Flicker Noise in Schottky Diodes.
INPUT POWER = –30 dBm
OUTPUT VOLTAGE (mV)
Flicker Noise
Reference to Figure 5 will show
that there is a junction of metal,
silicon, and passivation around the
rim of the Schottky contact. It is in
this three-way junction that flicker
noise[7] is generated. This noise
can severely reduce the sensitivity
of a crystal video receiver utilizing
a Schottky detector circuit if the
video frequency is below the noise
corner. Flicker noise can be
substantially reduced by the
elimination of passivation, but
such diodes cannot be mounted in
non-hermetic packages. p-type
silicon Schottky diodes have the
least flicker noise at a given value
of external bias (compared to ntype silicon or GaAs). At zero bias,
such diodes can have extremely
low values of flicker noise. For the
HSMS-285A series, the noise
temperature ratio is given in
Figure 29.
3.0 µA
25
10 µA
1.0 µA
15
0.5 µA
5
-55
-35
-15
5
25
45
65
85
TEMPERATURE (°C)
Figure 31. Output Voltage vs.
Temperature and Bias Current in the
5.80 GHz Voltage Detector using the
HSMS-286B Schottky.
10
Diode Burnout
Any Schottky junction, be it an RF
diode or the gate of a MESFET, is
relatively delicate and can be
burned out with excessive RF
power. Many crystal video
receivers used in RFID (tag)
applications find themselves in
poorly controlled environments
where high power sources may be
present. Examples are the areas
around airport and FAA radars,
nearby ham radio operators, the
vicinity of a broadcast band
transmitter, etc. In such
environments, the Schottky diodes
of the receiver can be protected by
a device known as a limiter
diode.[8] Formerly available only in
radar warning receivers and other
high cost electronic warfare
applications, these diodes have
been adapted to commercial and
consumer circuits.
Hewlett-Packard offers a complete
line of surface mountable PIN
limiter diodes. Most notably, our
HSMP-4820 (SOT-23) can act as a
very fast (nanosecond) powersensitive switch when placed
between the antenna and the
Schottky diode, shorting out the
RF circuit temporarily and
reflecting the excessive RF energy
back out the antenna.
reflow type of surface mount
assembly process.
0.026
0.07
0.035
0.016
Figure 32. PCB Pad Layout
(dimensions in inches).
SMT Assembly
Reliable assembly of surface
mount components is a complex
process that involves many
material, process, and equipment
factors, including: method of
heating (e.g., IR or vapor phase
reflow, wave soldering, etc.)
circuit board material, conductor
thickness and pattern, type of
solder alloy, and the thermal
conductivity and thermal mass of
components. Components with a
low mass, such as the SOT-323
package, will reach solder reflow
temperatures faster than those
with a greater mass.
HP’s SOT-323 diodes have been
qualified to the time-temperature
profile shown in Figure 33. This
profile is representative of an IR
After ramping up from room
temperature, the circuit board
with components attached to it
(held in place with solder paste)
passes through one or more
preheat zones. The preheat zones
increase the temperature of the
board and components to prevent
thermal shock and begin evaporating solvents from the solder paste.
The reflow zone briefly elevates
the temperature sufficiently to
produce a reflow of the solder.
The rates of change of temperature for the ramp-up and cooldown zones are chosen to be low
enough to not cause deformation
of the board or damage to components due to thermal shock. The
maximum temperature in the
reflow zone (TMAX) should not
exceed 235 °C.
These parameters are typical for a
surface mount assembly process
for HP SOT-323 diodes. As a
general guideline, the circuit board
and components should be exposed
only to the minimum temperatures
and times necessary to achieve a
uniform reflow of solder.
250
TMAX
Assembly Instructions
200
TEMPERATURE (°C)
SOT-323 PCB Footprint
A recommended PCB pad layout
for the miniature SOT-323 (SC-70)
package is shown in Figure 32
(dimensions are in inches). This
layout provides ample allowance
for package placement by automated assembly equipment
without adding parasitics that
could impair the performance.
150
Reflow
Zone
100
Preheat
Zone
Cool Down
Zone
50
0
0
60
120
180
TIME (seconds)
Figure 33. Surface Mount Assembly Profile.
[8]
Hewlett-Packard Application Note 1050, Low Cost, Surface Mount Power Limiters.
240
300
11
Package Dimensions
Outline SOT-323 (SC-70, 3 Lead)
1.30 (0.051)
REF.
2.20 (0.087)
2.00 (0.079)
1.35 (0.053)
1.15 (0.045)
0.650 BSC (0.025)
0.425 (0.017)
TYP.
2.20 (0.087)
1.80 (0.071)
0.10 (0.004)
0.00 (0.00)
0.30 REF.
0.25 (0.010)
0.15 (0.006)
1.00 (0.039)
0.80 (0.031)
10°
0.30 (0.012)
0.10 (0.004)
DIMENSIONS ARE IN MILLIMETERS (INCHES)
Part Number Ordering Information
No. of
Devices
Container
HSMS-285A-BLK [1]
3000
100
7" Reel
antistatic bag
HSMS-286A-TR1[2]
HSMS-286A-BLK
3000
100
7" Reel
antistatic bag
Part Number
HSMS-285A-TR1[1]
Notes:
1. “A” = B or C only
2. “A” = B, C, E or F
0.20 (0.008)
0.10 (0.004)
Device Orientation
REEL
TOP VIEW
END VIEW
4 mm
CARRIER
TAPE
USER
FEED
DIRECTION
8 mm
##
##
##
##
Note: “##” represents Package Marking Code.
COVER TAPE
Tape Dimensions and Product Orientation
For Outline SOT-323 (SC-70 3 Lead)
P
P2
D
P0
E
F
W
C
D1
t1 (CARRIER TAPE THICKNESS)
Tt (COVER TAPE THICKNESS)
K0
8° MAX.
A0
DESCRIPTION
5° MAX.
B0
SYMBOL
SIZE (mm)
SIZE (INCHES)
CAVITY
LENGTH
WIDTH
DEPTH
PITCH
BOTTOM HOLE DIAMETER
A0
B0
K0
P
D1
2.24 ± 0.10
2.34 ± 0.10
1.22 ± 0.10
4.00 ± 0.10
1.00 + 0.25
0.088 ± 0.004
0.092 ± 0.004
0.048 ± 0.004
0.157 ± 0.004
0.039 + 0.010
PERFORATION
DIAMETER
PITCH
POSITION
D
P0
E
1.55 ± 0.05
4.00 ± 0.10
1.75 ± 0.10
0.061 ± 0.002
0.157 ± 0.004
0.069 ± 0.004
CARRIER TAPE
WIDTH
THICKNESS
W
t1
8.00 ± 0.30
0.255 ± 0.013
0.315 ± 0.012
0.010 ± 0.0005
COVER TAPE
WIDTH
TAPE THICKNESS
C
Tt
5.4 ± 0.10
0.062 ± 0.001
0.205 ± 0.004
0.0025 ± 0.00004
DISTANCE
CAVITY TO PERFORATION
(WIDTH DIRECTION)
F
3.50 ± 0.05
0.138 ± 0.002
CAVITY TO PERFORATION
(LENGTH DIRECTION)
P2
2.00 ± 0.05
0.079 ± 0.002
www.hp.com/go/rf
For technical assistance or the location of
your nearest Hewlett-Packard sales office,
distributor or representative call:
Americas/Canada: 1-800-235-0312 or
408-654-8675
Far East/Australasia: Call your local HP
sales office.
Japan: (81 3) 3335-8152
Europe: Call your local HP sales office.
Data subject to change.
Copyright © 1998 Hewlett-Packard Co.
Obsoletes 5965-8838E
Printed in U.S.A.
5966-4282E (3/98)