Application Note, AN55132B - Aeroflex Microelectronic Solutions

Application Note AN55132B
Design of LOW COST High Isolation
20W and 50W Transmit and Receive
Antenna Switches
DESCRIPTION
This paper describes a high isolation 20 W transmit
and receive antenna switch for use in 500 MHz to
4 GHz wireless infrastructure applications such as
cellular GSM, CDMA, 3G and 4G-WCDMA, TDSCDMA; 802.11a, 802.11b, 802.11g WLAN / WiFi;
WiMax; ATSC and DVB-T Digital TV; and others
using low cost high performance discrete
MSWSSB-020-40 (D1 and D3) series-shunt and
MEST2G-020-15 (D2) series heat-shunt PIN diode
switch components. On the receive side, the circuit
uses a 2 GHz quarter wave transmission line
between the two series-shunt elements and on the
transmit side it uses a single series. It was optimized over the 500 MHz to 3.8 GHz bandwidth. It
requires no negative supply voltage. It uses 0.020
inch thick Rogers RO4350B substrate material with
1 oz copper clad and the component values and
part numbers can be found in table 2.
In the receive mode, with 50 mA bias and in the
frequency bands of most interest; the circuit provides the following performance over the 500 MHz
to 3.8 GHz bandwidth: less then 0.8 dB insertion
loss, better then 16 dB antenna port return loss and
an antenna-to-transmitter isolation of 27 dB at
2 GHz and 20 dB at 3.8 GHz.
The 50 W design can be accomplished with similar
performance as the 20W design by changing the
D2 diode. This design concept is very versatile and
can accompany different power levels and frequency bands by changing the D2 switch diode. Please
refer to the Switch Elements Matrix Table 3 for proper choice of D2, D1 and D3.
Table 1. 0.5 - 3.5 GHz Typical Performance 50 mA
At high power levels greater then 5 watts, the
reverse bias voltage values shown in figure 1 will
need to be increased. For example, at 20W and
500 MHz, the reverse bias voltage will need to be
greater then 45 volts.
Mode
Parameter
Tx
Insertion Loss
Return Loss
Isolation
0.5
17
70
0.5
19
62
0.7
30
62
Rx
Insertion Loss
Return Loss
Isolation
0.45
29
31
0.55
23
26
0.7
19
20
In the transmit mode and with 50 mA bias, the circuit provides the following performance over the
500 MHz - 3.8 GHz bandwidth: less then 0.75 dB
insertion loss, better then 17 dB transmitter port
return loss and less then 48 dB antenna-to-receiver isolation.
1 GHz 2 GHz 3.5 GHz
0V Rx
28V Tx
5V
28V Rx
0V Tx
R1
R5
R4
NO C10
C1
C12
Rx
D3
L6
D2
D1
L1
L4
¼λ
C2
C11
L3
L5
C17
Tx
L2
C9
C13, 14, 15, 16
R6
25V
C3, 4, 6, 7
C5
C18
R3
C8
R2
25V
Ant
5V
Figure 1. Schematic Diagram
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metelics-sales@aeroflex.com • www.aeroflex.com/metelics
Revision Date: 10/12/2011
Application Note
AN55132B
BOARD OUTLINE AND DIMENSIONS
Dimensions: 1.50 in (3.81 cm) x 2.10 in (5.33 cm)
Table 2. Parts List
Component
QTY
Description
Manufacture
P/N
R1, R4
2
0 Ω, 1 Amp, 0603 pkg
R2, R6
2
100 Ω, 1/10 W, 0603 chip Resistor, +5% KOA Speer or equivalent
RK73B1JTTE101J
R3, R5
2
82 Ω, 1/2 W, 1210 chip Resistor, +5%
KOA Speer or equivalent
RK73B2ETTE820J
C3, C15
2
10 pF, 250 VDC Capacitor, 0603 pkg
ATC
600S100JW 250XT
KOA Speer or equivalent
RK73Z1JTTE
C2, C8, C11
3
15 pF, 250VDC Capacitor, 0603 pkg
ATC
600S150JW 250XT
C6, C7, C13, C14
4
47pF, 250VDC Capacitor, 0603 pkg
ATC
600S470JW 250X
C1, C4, C5, C9,
C12, C16, C17
7
100 pF, 250VDC Capacitor, 0603 pkg
ATC
600S101JW 250XT
C18
2
0.2 pF, 250VDC Capacitor, 0603 pkg
ATC
600S0R2AW 250XT
L1 thru L6
6
47 nH, 600mA chip Inductor, 0603 pkg
Coilcraft
0603CS-47NXGLW
T1 thru T5
5
RF coax to co-planar edge connector
Johnson-Emerson
142-0761-831
J1 thru J6
6
Break Away Header on 0.100 centers
MOLEX or equivalent
22-28-4363
D2
1
Series PIN Diode in 2012 pkg
Aeroflex / Metelics
MEST2G-020-15
D1, 3
2
Series-Shunt PIN Diodes in 2012 pkg
Aeroflex / Metelics
MSWSSB-020-30
PCB
1
SPDT 2GHz QRT-W Ant SW Demo BD
Aeroflex / Metelics
A55132B, rev 2
2
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Revision Date: 10/12/2011
Application Note
AN55132B
Typical RF Performance at TA = 25 °C, Zo = 50 Ω, Small Signal P = -10 dBm
TRANSMIT MODE
Insertion Loss, Ant-Tx
Isolation, Ant-Rx
0
0
-10
-0.5
20 mA
-20
S21, dB
S21, dB
-1
20 mA
-1.5
50 mA
-2
50 mA
-30
-40
-50
-60
-70
-2.5
-80
-90
-3
0
1
2
3
0
4
1
2
3
4
Frequncy, GHz
Frequency, GHz
Return Loss, Tx Port
Return Loss, Ant Port
0
0
-5
20 mA
-5
-10
50 mA
50 mA
-15
S22, dB
S11, dB
-15
20 mA
-10
-20
-25
-30
-20
-25
-30
-35
-35
-40
-40
-45
-45
-50
-50
0
0
1
2
3
4
1
2
3
4
Frequncy, GHz
Frequncy, GHz
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Revision Date: 10/12/2011
3
Application Note
AN55132B
Typical RF Performance at TA = 25 °C, Zo = 50 Ω, Small Signal P = -10 dBm
RECEIVE MODE
Insertion Loss, Ant-Rx
Isolation, Ant-Tx
0
0
-10
-0.5
-20
S21, dB
S21, dB
-1
20 mA
-1.5
50 mA
-2
-30
20 mA
-40
50 mA
-50
-60
-2.5
-70
-80
-3
0
1
2
3
0
4
1
2
3
4
Frequncy, GHz
Frequncy, GHz
Return Loss, Rx Port
Return Loss, Ant Port
0
0
-5
-5
20 mA
50 mA
50 mA
-15
S11, dB
S22, dB
-15
20 mA
-10
-10
-20
-25
-30
-35
-20
-25
-30
-35
-40
-40
-45
-45
-50
0
1
2
Frequncy, GHz
3
4
-50
0
1
2
3
4
Frequncy, GHz
4
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Revision Date: 10/12/2011
Application Note
AN55132B
Table 3. Summary of Aeroflex / Metelics’ Surface Mount Switch Elements Products
Part Number
MEST2G-010-20
Configuration
Maximum
Power Watts
1.0
Insertion Loss
2.0 3.5
5.8
1.0
Isolation
2.0 3.5
5.8
Return Loss
1.0 2.0 3.5 5.8
18
30
Series 2012
10
0.30 0.30 0.35 0.35 31
26
MEST G-020-15
Series 2012
20
0.20 0.20 0.25 0.30 26
20
15
12
MEST2GFC-010-25
Series Chip
10
0.25
0.25 0.25 0.25 34
28
23
19
2
2
20
30
20 17
29
27
29 20
31
30
28 25
MEST G-080-25
Series CM27
80
0.20 0.22 0.25 0.45 30
25
20
18
30
30
22 14
MEST2G-150-20
Series CM26
150
0.20 0.25 0.30 0.40 26
21
17
13
30
34
16 17
MSWSE-005-15
Series 0503
4
0.20
0.21 0.28 0.48 24
18
14
11
32
28
22 14
MSWSE-010-15
Series 0503
10
0.25
0.25 0.25
--
17
12
7
--
22
27
25
--
MSWSE-010-16S
Series 0402P
10
0.05 0.08 0.10
--
21
15
11
--
34
29
25
--
MSWSE-20-05
Series 0503
20
0.03
--
9
--
--
--
37
--
--
--
MSWSE-040-10
Series 0805P
40
0.10
0.10 0.20
--
--
19
14
8
--
34
24
18
--
MSWSE-044-10
Series 0805P
40
0.12
0.20 0.35
--
15
10
5
--
39
30
19
--
MSWSE-050-10
Series 0805P
70
0.10
--
--
13
--
--
--
30
--
--
--
MSWSE-050-17
Series 0805P
40
0.05 0.06
--
--
19
12
--
--
30
25
--
--
MSWSER-070-10
Series 3023
80
0.04
--
--
--
8
--
--
--
22
--
--
--
MSWSER-100-05
Series 3023
80
0.21
--
--
--
10
--
--
--
24
--
--
--
MSWSH-020-30
Shunt 2012
20
0.05
0.10 0.20 0.35 35
32
30
28
34
25
18 15
0.03 0.07 0.12
--
--
MSWSH-040-30
Shunt 2012
40
0.28 37
34
30
26
30
24
20 15
MSWSH-100-30
Shunt CM22
300
0.10
0.12 0.20 0.32 33
30
30
28
30
24
20 15
MSWSHB-020-30
Shunt 2012
40
0.08
0.10 0.15 0.20 38
42
35
30
35
38
35 28
MSWSHC-040-40
Shunt 2615
40
0.10
0.18 0.22 0.38 40
50
52
53
30
27
22 19
MSWSS-020-40
Series Shunt 2012
20
0.15
0.20 0.35 0.55 63
52
45
35
30
25
18 13
0.11 0.13
MSWSS-040-30
Shunt Series 2012
20
0.09
58
50
43
36
38
35
33 30
MSWSSB-020-30
Series Shunt 2012
20
0.20 0.25 0.30 0.40 70
0.18
60
50
35
35
40
25 25
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Revision Date: 10/12/2011
5
Application Note
AN55132B
Thermal Considerations
This analysis starts from the diode junction and ends at
the heat sink. The heat sink design is left to the design
engineer, since system requirements may vary depending
on the specifics of the application and environment.
In the transmit mode, the MEST2G-020-15 series diode
power dissipation is equal to the input power minus the
reflected power (RL) and the insertion loss (IL) which are
both a function of frequency. At 2 GHz, the MEST2G-020-
Goal: Keep top of board temperature under 2012 package below this value
Looking at the diode by itself and from equation 3, the
de-rating curve shown in Figure 3 can be referenced for
board and heat sink thermal designs.
MEST 2G-020-15 Derating
(Freq = 2 GHz, IL = 0.2 dB)
25.00
15.00
10.00
5.00
15 insertion loss is 0.2 dB [1].
0.00
25
Mathematically and neglecting RL,
Pdis = Pin - Pout (W)
De-rate 15.4mW/°C
TC >113 °C
20.00
Pin, W
For long term reliability, the maximum diode junction temperature should never be exceeded; therefore, if the circuit is going to operate at the maximum transmit power
rating, then thermal design issues and possible heat sinking requirements need to be considered. To calculate
junction temperature, the power dissipation of the series
diode (D2) and the combined thermal resistance of the
diode, circuit board and heat sink need to be known.
50
(1)
75
100
125
150
175
200
Tcase , °C
Pin = 20 W g43 dBm
Figure 3
Need to calculate Pout (W),
Pout = Pin – Insertion Loss
(2)
Figure 4 below is another way of viewing the same information and can be used to track junction temperature. In
this figure, the case temperature is held steady at 25 °C.
= 43 dBm – 0.2 dB
= 42.8 dBm g 19.05 W
Junction Temperature vs Input Power
Then,
25
Pdis = 20 – 19.05 = 0.95 W
(2012 package ground lead) thermal resistance is 65
°C/W and the maximum junction temperature is 175 °C
[1].
Mathematically,
TJ = Tboard + Pdis x θJC (3)
= Tboard + 61.8 °C
Keep TJ < 175 °C then from equation 3,
Tboard < TJ - Pdis x θJC
< 175 – 61.8 °C
20
Pin, W
Given the maximum junction temperature, power dissipation and junction-to-case diode thermal resistance; the
maximum top-of-board temperature just below the metal
belly of the 2012 package can be calculated. Referring to
the data sheet, the MEST2G-020-15 junction-to-case
(Freq = 2 GHz, IL = 0.2 dB, Tc = 25 °C)
15
10
5
0
20.0
40.0
60.0
80.0
100.0
T J, °C
Figure 4. Junction temperature versus Pin while holding
case temperature at 25 °C
(4)
< 113.2 °C
6
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Revision Date: 10/12/2011
Application Note
AN55132B
Thermal Resistance Model and
θBH Calculation
The thermal resistance from the top of the board to the
heat sink for this circuit is primarily determined by the two
solder filled via holes just beneath the metal belly of the
2012 package and the two non-solder filled via holes just
adjacent to the package foot print as shown in Figure 6. The
diameter of the via holes are 0.010 inches and for this
example use 96.5Sn-3.5Ag solder whose thermal conductivity is 0.33 W/cm-C (0.84 W/in-C [2]. The via walls are plated with 1 oz copper (0.0014 inches) and the thermal conductivity for copper is 4 W/cm-C (10.2 W/in-C) [3]. The
height of the board is 0.020 inches.
Mathematically and for a solder filled via,
θSF_via = θsolder in parallel with θcopper (5)
Where,
θsolder = L / (A x σsolder)
(6)
= L / (π r2 * σsolder)
r solder = 0.005 – 0.0014,
(7)
θsolder = 0.02 / (π * 0.0036^2 * 0.84)
= 585 °C / W
Cross sectional area of copper going down via walls,
Figure 6. 2012 pkg foot print over PCB vias.
θcopper,
θcopper = L / (A x σCOPPER)
Now solve for θcopper,
θcopper = 0.02 / (3.78E-5 *10.2)
= 52 °C / W
Now calculate θSF_VIA from equation 4,
θSF_VIA = 52 in parallel with 585
= 48 °C / W
Acopper = AOD_hole – AID_copper_wall (8)
= π rh2 - π rs2
(9)
= π ( 0.005^2 – 0.0036^2)
To calculate board-to-heat sink thermal resistance, θBH,
have two solder filled vias and 2 unfilled 1 oz copper plated
vias all in parallel,
θBH
= 3.78E-5 in2
TJ
P
(10)
= (θSF_VIA || θSF_VIA) || (θCU || θCU) (11)
= (48 || 48) || (52 || 52)
= 12.5 °C / W
Combining the diode junction-to-case thermal resistance
with the board thermal resistance,
θJC
θJH
TTop of BD
θBH
TTop of HS
θHA
Tamb
= (θJC + θBH ) (12)
= 65 + 12.5
= 77.5 °C / W
And again, to keep TJ < 175 °C and using a modified form
of equation 3,
THS
< TJ - Pdis x θJH
< 175 – 73.6 °C
(13)
< 101 °C
Figure 5. Thermal resistance model.
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Revision Date: 10/12/2011
7
Application Note
AN55132B
If using this board in combination with the MEST2G-020-15
and if operating the transmitter at the maximum power
level, then the temperature between the board and heat
sink (THS) needs to be kept below the final number calculated above. This number, the power dissipation and the
maximum ambient temperature will determine the heat sink
requirements as shown in equation 14 below.
REFERANCES
[1] Aeroflex Metelics Inc., “MEST2G-020-15 Data Sheet”
[2] Microwaves101.com, “Solder for Microwave
Assemblies”
[3] The Engineering Tool Box, “Thermal Conductivity of
Some Common Materials”
θHA < (TJ - Pdis ( θJC + θBH)) – TAMB_max (14)
Pdis
Equations 12 & 13 have already been solved,
θHA < 101 – TAMB_max
Pdis
SUMMARY
A 20W and 50W 500 MHz to 4 GHz antenna transmit and
receive generic switch design has been presented that
uses Aeroflex-Metelics’ low cost high performance discrete
MSWSS-020-40 series-shunt and MEST2G-020-15 shunt
PIN diode switch elements. The 20W design provides very
low insertion loss along with high antenna-to-receiver isolation making it ideal for most wireless infrastructure applications. In addition, a thermal analysis was provided that
shows that this switch design can conservatively handle its
maximum rated power provided sufficient heat sinking is
incorporated into the system design.
United States
TEL: 408-737-8181
Fax: 408-733-7645
www.aeroflex.com/metelics
metelics-sales@aeroflex.com
Aeroflex / Metelics, Inc. reserves the right to make changes to any products
and services herein at any time without notice. Consult Aeroflex or an
authorized sales representative to verify that the information in this data
sheet is current before using this product. Aeroflex does not assume any
responsibility or liability arising out of the application or use of any product
or service described herein, except as expressly agreed to in writing by
Aeroflex; nor does the purchase, lease, or use of a product or service from
Aeroflex convey a license under any patent rights, copyrights, trademark
rights, or any other of the intellectual rights of Aeroflex or of third parties.
Copyright 2008 Aeroflex / Metelics. All rights reserved.
Revision Date: 10/12/2011
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