APPLICATION NOTE SKY12212-478LF: Low Frequency Tuning Introduction Abstract The SKY12212-478LF is a high power handling, Single-Pole, Double-Throw (SPDT) silicon PIN diode switch. The device operates over the 50 MHz to 2.7 GHz band. It features low insertion loss, excellent power handling, and superb linearity with low DC power consumption. The SKY12212-478LF is well-suited for use as a high power transmit/receive switch in a variety of telecommunication systems such as Sat-Com, Cable TV, WiMAX, TD-SCDMA, or LTE base stations. The device is provided in a 4 x 4 mm, 16-pin Quad Flat No-Lead (QFN) package. The SKY12212-478LF block diagram is shown in Figure 1. The operating range specified in the standard data sheet for the SKY12212-478LF is 50 MHz to 2.7 GHz. The part has the capability to operate at lower frequencies with high input power. With modifications to the external bias circuitry, the SKY12212478LF can operate from 20 MHz to 2700 MHz with low insertion loss, high isolation and 100 W power handling capability. ANT TX RX RX_BIAS Theory of Operation Operating at frequencies below 200 MHz presents problems not seen at higher frequencies. The series transmit diode has a characteristic to self-rectify at low RF frequencies and high power levels. In the transmit mode, high harmonic content is observed at input power levels above 42 dBm. This requires an innovative solution to reduce harmonic levels and maintain low TX insertion loss and high RX isolation up to 100 Watts. The solution is to create an innovative bias decoupling network that reduces the harmonic distortion at low frequencies and high power levels. Exposed Paddle S2403 Figure 1. SKY12212-478LF Block Diagram Skyworks Green™ products are compliant with all applicable legislation and are halogen-free. For additional information, refer to Skyworks Definition of Green™, document number SQ04-0074. At high power levels, a high harmonic content occurs because the RF input frequency is close to the SRF of the RF choke/ DC bias inductors. As a result, the switch goes into an early compression state at power levels > 42 dBm. The bias inductors provide the RF choking on the DC bias lines without degrading the input and output VSWR. The inductor value must be selected properly as it affects the RF match. The solution is to modify the bias network by adding an additional inductor that has an SRF above the RF input. The inductors are positioned in series to each other with the highest value inductor placed next to the switch. This provides the highest RF reactance for the best RF blocking and best match at lower operating frequencies. The evaluation board schematic diagram for the SKY12212-478LF for low frequency operation is shown in Figure 2. The low frequency tuned evaluation board is shown in Figure 3. The bill of materials is shown in Table 1. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 203126A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • February 14, 2014 1 APPLICATION NOTE • SKY12212-478LF: LOW FREQUENCY TUNING Antenna Port Bias Input R1 33 Ω C13 1 μF C12 10000 pF C10 10000 pF Transmitter Input Port L9 1800 nH L7 390 nH L10 390 nH N/C 16 15 14 C11 10000 pF 13 Transmitter Port Bias Input L8 1800 nH 12 N/C 1 Antenna Port L4 390 nH Receiver Port Bias Input L3 1800 nH Exposed paddle connected to ground 10 N/C 3 L6 820 nH R2 560 Ω RX Bias 9 N/C 4 U1 SKY12212 5 C7 10000 pF Receiver Output Port 11 N/C 2 C1 10000 pF C9 10000 pF 6 7 8 R3 560 Ω N/C C2 10000 pF Notes: Y0669 R1 value set for 5 V, 100 mA bias R2 and R3 values set for 28 V, 100 mA bias Figure 2. SKY12212-478LF Evaluation Board Schematic for Low Frequency Tuning Diagram Y0667 Figure 3. SKY12212-478LF Evaluation Board Layout for Low Frequency Tuning Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 2 February 14, 2014 • Skyworks Proprietary lnformation • Products and Product Information are Subject to Change Without Notice • 203126A APPLICATION NOTE • SKY12212-478LF: LOW FREQUENCY TUNING Table 1. SKY12212-478LF Evaluation Board Bill of Materials Component Value Units Size Manufacturer Mfr Part Number Characteristics C1, C2, C7, C9, C10, C11, C12 10000 pF 0603 Murata GRM188R7H103K X7R, 50 V, ±5% C13 1 F 0603 Murata GRM188R71C105K X7R, 16 V, ±10% L3, L8, L9 1800 nH 0805 Coil Craft 0805LS-182XJLB ±5%, SRF 246 MHz L4, L7, L10 390 nH 0805 TOKO LL2012-FR39K ±10%, SRF 330 MHz L6 820 nH 0603 Coil Craft 00603LS-821XJLB ±5%, SRF 410 MHz R1 33 1206 Panasonic ERJ8ENF33R0V 250 mW, 1% R2, R3 560 2512 Multicomp MCPWR12FTEA5600 1.5 W, 1% 4 x 4 x 1.5 mm Skyworks SKY12212-478LF Skyworks EN33-D785-001 U1 EVB Typical Performance Characteristics 0.0 0 –0.4 –5 –0.8 –10 –1.2 –1.6 –2.0 –15 –20 –25 ANT Return Loss (S11) with ANT to RX in Insertion Loss State RX Return Loss (S22) with ANT to RX in Insertion Loss State TX Return Loss (S33) with ANT to TX in Insertion Loss State ANT Return Loss (S11) with ANT to TX in Insertion Loss State RX Return Loss (S22) with ANT to TX in Insertion Loss State TX Return Loss (S33) with ANT to RX in Insertion Loss State –30 –2.4 S31: ANT to TX in Insertion Loss State 0.4 0.8 1.2 1.6 2.0 2.4 Y0670 –3.0 0.0 –35 S21: ANT to RX in Insertion Loss State –2.8 –40 0.0 2.6 0.4 0.8 1.6 2.0 2.4 2.6 Frequency (GHz) Frequency (GHz) Figure 5. Return Loss vs Frequency Figure 4. Insertion Loss vs Frequency 0 0 –0.2 Insertion Loss (dB) –10 –20 –30 –40 –0.4 –0.6 30 MHz 50 MHz 100 MHz 300 MHz 700 MHz 1000 MHz –0.8 Y0673 –1.0 –50 S21: ANT to RX Isolation with ANT to TX in Insertion Loss State S31: ANT to TX Isolation with ANT to RX in Insertion Loss State –60 0.0 0.4 0.8 1.2 1.6 2.0 Frequency (GHz) Figure 6. Isolation vs Frequency 2.4 2.6 Y0672 Isolation (dB) 1.2 Y0671 Return Loss (dB) Insertioin Loss (dB) (TOP = +25°C, PIN = 0 dBm, ANT_DC = 5 V, TX_DC, RX_BIAS and RX_DC= 0/28 V, Characteristic Impedance [ZO] = 50 Ω, Unless Otherwise Noted) –1.2 30 35 40 45 50 55 Power In (dBm) Figure 7. Insertion Loss vs CW Input Power vs Frequency Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 203126A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • February 14, 2014 3 APPLICATION NOTE • SKY12212-478LF: LOW FREQUENCY TUNING Summary Operating high power PIN diode switches at frequencies below 200 MHz presents problems not seen at higher frequencies. In the transmit mode, high harmonic content is observed at input power levels above 42 dBm. The solution is to create an innovative bias decoupling network with two series RF chokes to reduce the harmonic distortion observed at low frequencies and high power levels. Copyright © 2014 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. 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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 4 February 14, 2014 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 203126A