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BA T15 -04 W
BDTIC
The Lo w Bar ri er Sc hottk y Di o de
BA T15 -04 W as a Mi xe r f or Ku -Ba nd
LN Bs
Appl i c ati o n N ote A N 198
Revision: Rev. 1.0
2010-09-29
RF and P r otec ti on D evi c es
www.BDTIC.com/infineon
BDTIC
Edition 2010-09-29
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2010 Infineon Technologies AG
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BAT15-04W
BAT15-04W LNB Mixer
Application Note AN198
Revision History: 2010-09-29
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Application Note AN198, Rev. 1.0
3 / 12
2010-09-29
BAT15-04W
BAT15-04W LNB Mixer
List of Content, Figures and Tables
Table of Content
1
Introduction ........................................................................................................................................ 5
2
RF Schottky Diode ............................................................................................................................. 6
3
3.1
Design concept of a singly balanced mixer .................................................................................... 8
Simulation results ................................................................................................................................. 9
Author
11
List of Figures
BDTIC
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Blockdiagram of a universal Ku-Band LNB .......................................................................................... 5
Specified Frequencies for LNB (Ku-Band) ........................................................................................... 6
The serial resistance Rs causes at high currents (Ih) a voltage drop ∆U between the extrapolated
straight line and the measured I(U) curve. The ideality factor n corresponds to the gradient of the
IU-characteristic in forward operation and can be extracted within the linear region of the log(I(U))
diagram ................................................................................................................................................ 7
Mixer Topology ..................................................................................................................................... 8
Conversion Gain over RF frequency with LO Power at 10.6 GHz as a parameter. ............................ 9
Conversion Gain over LO power at 10.6 GHz, RF power is -30 dBm at 12.1 GHz ............................. 9
Conversion Gain vs RF power at 12.1 GHz, LO power is 0 dBm at 10.6 GHz .................................. 10
List of Tables
Table 1
Universal LNB specification ................................................................................................................. 5
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Application Note AN198, Rev. 1.0
4 / 12
2010-09-29
BAT15-04W
BAT15-04W LNB Mixer
Introduction
1
Introduction
This application note shows Infineon’s BAT15-04W low barrier Schottky diode used in a singly balanced mixer
for Ku-band applications. The frequency band covered in this report is the high band from 11.55 GHz to 12.75
GHz.
A functional block diagram of a universal LNB is shown in Figure 1. The building blocks for which Infineon offers
devices are depicted in red.
The abbreviation H (horizontal) and V (vertical) represents the electrical polarization of the electromagnetic
wave transmitted by the satellite. At first the received linearly polarized wave is amplified via a multistage
amplifier chain and afterwards down converted by the active mixer. The IF signal is further amplified so that the
following data processing can be applied.
BDTIC
DRO1
LNA1
9.75 GHz
H
LNA2
LNA3
IF Amplifiers
10.7 – 12.75 GHz
IF
950-2150MHz
V
10.6 GHz
DRO2
Figure 1
Blockdiagram of a universal Ku-Band LNB
An overview of the occupied frequencies is shown in Table 1. A graphical view of the frequency bands is
depicted in Figure 2 which visualizes also the down conversion of the received RF signal bands from the RFLowband / RF-Highband to the IF-Band (0.95GHz to 2.15GHz). These received bands include the TV-channels
which are transmitted from the geostationary satellites.
Table 1
Universal LNB specification
Lowband
Highband
Switching Mode
LO
9.75 GHz
10.6 GHz
RF
(10.70 – 11.9) GHz
(11.55 – 12.75)GHz
- Switching between the two frequency bands
(local oscillators) is done by a 22kHz tone
generated by the receiver when selecting a
certain channel
- Switching between horizontal and vertical
polarization is done by the voltage of the power
supply when selecting a certain channel
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Application Note AN198, Rev. 1.0
5 / 12
2010-09-29
BAT15-04W
BAT15-04W LNB Mixer
RF Schottky Diode
BDTIC
Figure 2
Specified Frequencies for LNB (Ku-Band)
2
RF Schottky Diode
The device characteristic of the Schottky diode is similar to a typical one sided abrupt pn diode which follows the
same current voltage characteristic as being shown in equation (1). However, there are some magnificent
differences between the pn junction diode and the Schottky diode. For example, the Schottky diode exhibits a
lower forward voltage drop (0.15V to 0.45V) than the pn diode (0.7V to 1.7V). Furthermore, the voltage drop of
Schottky diodes in forward direction can be adjusted by the applied contact material and also zero biased
Schottky diodes can be processed based on p-doped materials.
Moreover, pn junction diodes belong to minority semiconductor devices suffering on the recombination velocity
of the minority carriers in the space charge region, whereas, the Schottky diodes are controlled by the charge
transport over the barrier from the majority carriers. This leads to very fast switching action of the Schottky
diodes and makes it very attractive for RF application in the mm wave range like mixers.

 qU d  
 − 1
I = I S (T ) ⋅  exp
n
k
T

 

(1)
(k: Boltzmann factor, n: ideality factor, IS: saturation current, Ud: voltage, T: temperature)
17
In normal forward operation at room temperature and moderate doping concentration (Nd < 10
following charge transports can be identified:
−
−
−
−
-3
cm ) the
Transport of electrons from semiconductor over the barrier to the metal
Tunneling of electrons through the barrier
Recombination in the space charge region
Injection of holes from the metal to the semiconductor
The ideality factor n corresponds to the gradient of the IU-characteristic in forward operation and can be
extracted within the linear region of the log(I(U)) diagram as shown in Figure 3Figure 3. Furthermore, the
nonlinear behavior of the device corresponds to the fast switching from the conductive state to the nonconductive state by the LO signal. As the ideality factor n increases, the nonlinearity of the device is reduced
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Application Note AN198, Rev. 1.0
6 / 12
2010-09-29
BAT15-04W
BAT15-04W LNB Mixer
RF Schottky Diode
and the capability for frequency mixing is reduced, as well. Therefore, for mixer applications the ideality factor of
the Schottky diode should be as small as possible, typically, smaller than 1.1.
The voltage dependent junction capacitance Cj follows the equation (2) with the model parameter Uj which
refers to the junction voltage and M as the grading coefficient (Μ = 0.5 for a uniformly doped diode).

U 
C j (U d ) = C j 0 ⋅ 1 − d 

U j 

−M
(2)
Based on the small signal equivalent circuit the frequency conversion is also directly influenced by the serial
resistance Rs and the junction capacitance Cj as shown in equation (3). Both Cj0 and Rs should be as small as
possible and this characteristic figure of merit is represented by the cutoff frequency fc which should be as high
as possible (3). The serial resistance Rs decreases and the junction capacitance Cj0 increases by increasing the
device area A so that a first order analysis shows that the cut off frequency is independent of the junction area.
However, second order effects reveal that the cut off frequency can be increased by decreasing the junction
area.
BDTIC
These and the non-linear junction capacitance Cj affect the mixer performance directly so that we have to
optimize the Schottky diode appropriately in order to meet the mixer specification.
Figure 3
The serial resistance Rs causes at high currents (Ih) a voltage drop ∆U between the
extrapolated straight line and the measured I(U) curve. The ideality factor n corresponds to
the gradient of the IU-characteristic in forward operation and can be extracted within the
linear region of the log(I(U)) diagram
www.BDTIC.com/infineon
Application Note AN198, Rev. 1.0
7 / 12
2010-09-29
BAT15-04W
BAT15-04W LNB Mixer
Design concept of a singly balanced mixer
3
Design concept of a singly balanced mixer
The topology of the mixer used in this concept study is shown in Figure 4. It is a simplified schematic of the
schematic actually used in simulation.
The amplified RF signal and the LO signal are applied at the sum port and the delta port of a 180°-hyb rid (e.g. a
rat-race coupler). The balanced LO signal at the hybrid’s output drives (“pumps”) the two Schottky diodes
included in the BAT15-04W package. The IF signal is fed from the common pin of the two diodes though a
lowpass filter to the IF output pin. Additionally a radial open stub suppresses the RF and LO signal at the IF
output
Two shorted stubs are used to shorten the IF mixing products on the “RF side” of the mixer while providing a
high impedance at LO and RF frequency. Shortening unwanted signal at the single ports reduces conversion
loss significantly.
BDTIC
W=0.2 mm
L=2.2 mm
P=1
Z=50 Ohm
2
RF
1
P=2
Z=50 Ohm
3
0
0
2
IND
ID=L1
L=4.2 nH
1
0
180
P=3
Z=50 Ohm
IF
NET="BAT1504W"
4
LO
3
CAP
ID=C1
C=0.8 pF
CAP
ID=C2
C=0.8 pF
W=0.2 mm
L=2.2 mm
Figure 4
Mixer Topology
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Application Note AN198, Rev. 1.0
8 / 12
2010-09-29
BAT15-04W
BAT15-04W LNB Mixer
Design concept of a singly balanced mixer
3.1
Simulation results
Conversion Gain vs. RF frequency
-4
p6
-5
p5
Gconv (dB)
-6
p4
p3
p2
BDTIC
-7
p1
-8
-9
p1: P_LO = 0
p2: P_LO = 2
p3: P_LO = 4
p4: P_LO = 6
p5: P_LO = 8
p6: P_LO = 10
-10
11.6 11.7 11.8 11.9
Figure 5
12 12.1 12.2 12.3 12.4 12.5 12.6 12.7
Frequency (GHz)
Conversion Gain over RF frequency with LO Power at 10.6 GHz as a parameter.
Conversion Gain vs. P_LO
-4
-5
Gconv (dB)
-6
-7
-8
-9
-10
-4
0
4
8
12
16
Power (dBm)
Figure 6
Conversion Gain over LO power at 10.6 GHz, RF power is -30 dBm at 12.1 GHz
www.BDTIC.com/infineon
Application Note AN198, Rev. 1.0
9 / 12
2010-09-29
BAT15-04W
BAT15-04W LNB Mixer
Design concept of a singly balanced mixer
Conversion Gain vs. P_RF
-5
Gconv (dB)
-6
-7
BDTIC
-8
-9
-10
-30
Figure 7
-25
-20
-15
Power (dBm)
-10
-5
0
Conversion Gain vs RF power at 12.1 GHz, LO power is 0 dBm at 10.6 GHz
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Application Note AN198, Rev. 1.0
10 / 12
2010-09-29
BAT15-04W
BAT15-04W LNB Mixer
Author
Author
Dietmar Stolz, Staff Engineer of Business Unit “RF and Protection Devices”
BDTIC
www.BDTIC.com/infineon
Application Note AN198, Rev. 1.0
11 / 12
2010-09-29
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AN198