Application Note AN55131B Design of LOW COST High Performance 20W and 50W Transmit and Receive Antenna Switches DESCRIPTION Figure 1. This paper describes a 20 W SPDT switch for use in 500 MHz to 4 GHz wireless infrastructure applications such as cellular GSM, CDMA, 3G and 4G-WCDMA, TD-SCDMA; 802.11a, 802.11b, 802.11g WLAN / WiFi; WiMax; ATSC and DVB-T Digital TV; and others using low cost discrete MSWSS-020-40 (D1) and MEST2G-020-15 (D2) PIN diode switch components. The circuit was optimized over the 500 MHz to 3.8 GHz bandwidth and it requires no negative supply voltage. It uses 0.020 inch thick Rogers RO4350B substrate material with 1 oz copper clad. The component values and part numbers can be found in Table 2. Table 1. 0.5 - 3.8 GHz Performance Summary Mode Parameter Tx Insertion Loss Return Loss Isolation 900 MHz Isolation 2 GHz Isolation 3.8 GHz < > > > > 0.5 dB 18 dB 58 dB 50 dB 32 dB Rx Insertion Loss Return Loss Isolation 900 MHz Isolation 2 GHz Isolation 3.8 GHz < > > > > 0.6 dB 15 dB 32 dB 27 dB 22 dB 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. 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 0.5 dB insertion loss, better then 18 dB transmitter port return loss and an antenna-to-receiver isolation of 50 dB at 2 GHz and 32 dB at 3.8 GHz. In the receive mode and with 50 mA bias, the circuit provides the following performance over the 500 MHz to 3.8 GHz bandwidth: less then 0.6 dB insertion loss, better then 15 dB antenna port return loss and an antenna-to-transmitter isolation of 27 dB at 2 GHz and 22 dB at 3.8 GHz. The 50 W design can be accomplished with similar performance as the 20 W 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 Switch Elements Matrix Table 3 for proper choice of D2 and D1. Value SPDT SWITCH SCHEMATIC 28V Rx 0V Tx 0V Rx 28V Tx R1 R4 C10 C1 Rx D2 D1 L1 L4 C2 C11 L3 L2 C13 C8 C9 C3, 4, 6, 7 C5 Tx R3 C12 R2 25V Ant 5V Figure 1 TEL: 603-641-SEMI (7364) • FAX: 408-733-7645 [email protected] • www.aeroflex.com/metelics Revision Date: 10/12/2011 Application Note AN55131B BOARD OUTLINE AND DIMENSIONS C12 C13 Dimensions: 1.50 in (3.81 cm) x 2.10 in (5.33 cm) Table 2. Parts List Component 2 QTY Description Manufacture P/N R1, R4 2 0 Ω, 1 Amp, 0603 pkg KOA Speer or equivalent' RK73Z1JTTE R2 1 100 Ω, 1/10W, 0603 chip Resistor, +5% KOA Speer or equivalent' RK73B1JTTE101J R3 1 200 Ω, 1/10W, 0603 chip Resistor, +5% KOA Speer or equivalent' RK73B1JTTE201J C2, C9, C11 1 20 pF, 250VDC Capacitor, 0603 pkg ATC 600S200JW 250XT C1, C5, C6, C7, C8, C10 6 47 pF, 250VDC Capacitor, 0603 pkg ATC 600S470JW 250XT C3 1 10 pF, 250VDC Capacitor, 0603 pkg ATC 600S100JW 250XT C4 1 100 pF, 250VDC Capacitor, 0603 pkg ATC 600S101JW 250XT C12, C13 2 0.2 pF, 250VDC Capacitor, 0603 pkg ATC 600S0R2AW 250XT L1 thru L4 4 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 J4 4 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 1 Series-Shunt PIN Diodes in 2012 pkg Aeroflex / Metelics MSWSS-020-40 PCB 1 SPDT Ant SW Demo BD 2012 PKG Aeroflex / Metelics A55131B, rev 2.3 TEL: 603-641-SEMI (7364) • FAX: 408-733-7645 • [email protected] • www.aeroflex.com/metelics Revision Date: 10/12/2011 Application Note AN55131B 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 -1 S21, dB S21, dB -20 20 mA -1.5 50 mA -2 50 mA -30 -40 -50 -2.5 -60 -3 0 1 2 3 -70 4 0 1 3 4 Frequency, GHz Frequency, GHz Return Loss, Tx Port Return Loss, Ant Port 0 0 -5 -10 20 mA -5 20 mA 50 mA -10 50 mA -15 -15 -20 -20 S22, dB S11, dB 2 -25 -30 -25 -30 -35 -35 -40 -40 -45 -45 -50 -50 0 1 2 Frequency, GHz 3 4 0 1 2 3 Frequency, GHz TEL: 603-641-SEMI (7364) • FAX: 408-733-7645 • [email protected] • www.aeroflex.com/metelics Revision Date: 10/12/2011 4 3 Application Note AN55131B 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 S21, dB S21, dB -20 -1 20 mA -1.5 50 mA -2 -30 20 mA -40 100 mA -50 -2.5 -60 -3 0 1 2 3 -70 4 0 1 Return Loss, Rx Port 4 0 -5 20 mA -5 20 mA -10 50 mA -10 50 mA -15 -15 -20 -20 S11, dB S22, dB 3 Return Loss, Ant Port 0 -25 -30 -25 -30 -35 -35 -40 -40 -45 -45 -50 -50 0 1 2 Frequncy, GHz 4 2 Frequncy, GHz Frequency, GHz 3 4 0 1 2 3 4 Frequncy, GHz TEL: 603-641-SEMI (7364) • FAX: 408-733-7645 • [email protected] • www.aeroflex.com/metelics Revision Date: 10/12/2011 Application Note AN55131B Table 3, Summary of Aeroflex / Metelics’ Surface Mount Switch Elements Products Part Number 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 MEST2G-010-20 Series 2012 10 0.30 0.30 0.35 0.35 31 26 20 18 30 30 20 17 MEST2G-020-15 Series 2012 20 0.20 0.20 0.25 0.30 26 20 15 12 29 27 29 20 2 Series Chip 10 0.25 0.25 0.25 0.25 34 28 23 19 31 30 28 25 2 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 -- MEST GFC-010-25 MSWSE-20-05 Series 0503 20 0.03 MSWSE-040-10 Series 0805P 40 0.10 0.10 0.20 -- -- MSWSE-044-10 Series 0805P 40 0.12 0.20 0.35 MSWSE-050-10 Series 0805P 70 0.10 MSWSE-050-17 Series 0805P 40 MSWSER-070-10 Series 3023 MSWSER-100-05 Series 3023 MSWSH-020-30 Shunt 2012 20 0.05 MSWSH-040-30 Shunt 2012 40 0.03 0.07 0.12 MSWSH-100-30 Shunt CM22 300 MSWSHB-020-30 Shunt 2012 MSWSHC-040-40 Shunt 2615 MSWSS-020-40 Series Shunt 2012 MSWSS-040-30 Shunt Series 2012 MSWSSB-020-30 Series Shunt 2012 -- 9 -- -- -- 37 -- -- -- -- 19 14 8 -- 34 24 18 -- -- 15 10 5 -- 39 30 19 -- -- -- 13 -- -- -- 30 -- -- -- 0.05 0.06 -- -- 19 12 -- -- 30 25 -- -- 80 0.04 -- -- -- 8 -- -- -- 22 -- -- -- 80 0.21 -- -- -- 10 -- -- -- 24 -- -- -- -- 0.10 0.20 0.35 35 32 30 28 34 25 18 15 0.28 37 34 30 26 30 24 20 15 0.10 0.12 0.20 0.32 33 30 30 28 30 24 20 15 40 0.08 0.10 0.15 0.20 38 42 35 30 35 38 35 28 40 0.10 0.18 0.22 0.38 40 50 52 53 30 27 22 19 20 0.15 0.20 0.35 0.55 63 52 45 35 30 25 18 13 20 0.09 0.11 0.13 58 50 43 36 38 35 33 30 20 0.20 0.25 0.30 0.40 70 60 50 35 35 40 25 25 0.18 TEL: 603-641-SEMI (7364) • FAX: 408-733-7645 • [email protected] • www.aeroflex.com/metelics Revision Date: 10/12/2011 5 Application Note AN55131B 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 derating curve shown in Figure 2 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) Pin = 20 W g 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 43 dBm Figure 2 Need to calculate Pout (W), Pout = Pin – Insertion Loss (2) Figure 3 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 3. Junction temperature versus Pin while holding case temperature at 25 °C (4) < 113.2 °C 6 TEL: 603-641-SEMI (7364) • FAX: 408-733-7645 • [email protected] • www.aeroflex.com/metelics Revision Date: 10/12/2011 Application Note AN55131B 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 5. 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 5. 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) = 3.78E-5 in2 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 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 (13) < 175 – 73.6 °C < 101 °C Figure 4. Thermal resistance model TEL: 603-641-SEMI (7364) • FAX: 408-733-7645 • [email protected] • www.aeroflex.com/metelics Revision Date: 10/12/2011 7 Application Note AN55131B 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 20 W and 50 W 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 [email protected] 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 Our passion for performance is defined by three attributes represented by these three icons: solution-minded, perofrmance-driven and customer-foocused.