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Silicon Laboratories EFR32 Matching Manual
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Silicon Laboratories EFR32 Matching Manual

Silicon Laboratories EFR32 Matching Manual

2.4 ghz
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AN930: EFR32 2.4 GHz Matching Guide
The EFR32 devices include chip variants that provide 2.4 GHz-
only operation, sub-GHz-only operation, or dual-band (2.4 GHz
and sub-GHz) operation. In addition, the EFR32 chips are availa-
ble in a 7x7 mm 48-pin package and a 5x5 mm 32-pin package.
This application note describes the matching techniques applied
to the EFR32 Wireless Gecko Portfolio in the 2.4 GHz band.
For information on PCB layout requirements for proper 2.4 GHz operation, refer to
AN928: EFR32 Layout Design
for information on minimizing the bill of materials. For information on the matching pro-
cedure for the sub-GHz path, refer to
silabs.com | Building a more connected world.
Guide. Refer to
AN933: EFR32 2.4 GHz Minimal BOM
AN923: EFR32 sub-GHz Matching
KEY POINTS
• Description of the applied 2.4 GHz
matching networks and techniques for the
EFR32 device
• Detailed discussion of the design steps
and design examples
• Three different EFR32 versions: 7x7 mm
48-pin dual band version, 7x7 mm 48-pin
2.4 GHz version, and 5x5 mm 32-pin 2.4G
Hz version.
Guide.
• Measured TX spectrum and RX sensitivity
results
Rev. 0.4

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Summary of Contents for Silicon Laboratories EFR32

  • Page 1 EFR32 device This application note describes the matching techniques applied • Detailed discussion of the design steps to the EFR32 Wireless Gecko Portfolio in the 2.4 GHz band. and design examples • Three different EFR32 versions: 7x7 mm For information on PCB layout requirements for proper 2.4 GHz operation, refer to...
  • Page 2 AN923: EFR32 sub-GHz Matching Guide • AN928: EFR32 Layout Design Guide • AN933: EFR32 2.4 GHz Minimal BOM • AN0002.1: EFM32 and EFR32 Wireless Gecko Series 1 Hardware Design Considerations silabs.com | Building a more connected world. Rev. 0.4 | 2...

  • Page 3: Efr Rf Architecture Overview

    2. EFR RF Architecture Overview The EFR32 chip family has separate sub-GHz and 2.4 GHz RF front ends. The sub-GHz part is not detailed here. The 2.4 GHz RF front end architecture of the EFR32 chip is shown in the figure below.
  • Page 4 2.4 GHz RF Matching Design Steps 3. 2.4 GHz RF Matching Design Steps 2.4 GHz RF matching design for EFR32 chips consists of the following steps: 1. Determine the optimum termination impedance for the PA. 2. Choose the RF matching topology.
  • Page 5 AN930: EFR32 2.4 GHz Matching Guide 2.4 GHz RF Matching Design Steps In real radio links, the TX power and the receiver sensitivity together (i.e., the link budget) determine the range. So, with the applied TX termination impedance, the impedance match in RX mode should also be acceptable. Fortunately, the RX sensitivity is quite immune to impedance variations.
  • Page 6 AN930: EFR32 2.4 GHz Matching Guide 2.4 GHz RF Matching Design Steps 3.3 Initial Design with Ideal, Loss-Free Elements After choosing the best topology for the application, the third step of the matching design procedure is to generate a lumped element schematic of the match with ideal loss-free elements and without PCB parasitics.
  • Page 7 AN930: EFR32 2.4 GHz Matching Guide 2.4 GHz RF Matching Design Steps Figure 3.2. Basic Two-Element Matching Techniques with Ideal Lumped Elements 3.4 Design with Parasitics and Losses The fourth step should be to take into account the parasitics of the discrete components. For Silicon Labs reference designs 0402 or 0201-sized, surface mount device (SMD) elements are used.
  • Page 8 AN930: EFR32 2.4 GHz Matching Guide 2.4 GHz RF Matching Design Steps 3.4.1 Effects of SMD Discrete Parasitics and Losses Inductors are the most critical elements in matching networks due to their higher cost and lower Q compared to SMD capacitors. There are three basic SMD inductor types: wirewound, metal-film-based, and multilayer.
  • Page 9 AN930: EFR32 2.4 GHz Matching Guide 2.4 GHz RF Matching Design Steps Figure 3.4. 2-Element Match Mistuning with Real SMD Elements 3.4.2 Rough Estimation of PCB Parasitics In addition to the discrete parasitics, the following PCB trace parasitics also have significant effects: •...
  • Page 10 2.4 GHz RF Matching Design Steps The figure below shows the reference plane positions used in the simulations for the EFR32 IC 2G4RF_IOP pin and for the discrete SMD pins. Since the IC pin covers the whole pad area, the reference plane falls to the geometric center of the PCB pad. With the dis- crete SMD elements, the reference plane is put at the ends of the SMD soldering pin.
  • Page 11 AN930: EFR32 2.4 GHz Matching Guide 2.4 GHz RF Matching Design Steps Figure 3.7. 2-Element Lumped Element Match with Discrete Models of PCB Layout Parasitics These PCB parasitics detune the matching network in the same way as the SMD parasitics described previously. Here, the further de- crease of the applied series inductor (L0) to 1.8 nH and parallel capacitor (C0) to 1.1 pF compensates for the PCB parasitic effects.
  • Page 12 The figure below shows a simulated layout. This layout is used for both the ladder two-element and four-element matches. Here, the 2G4RF_IOP pin of the EFR32 chip is connected to Port 2. The L0 inductor is connected between Ports 3 and 4, the C0 capacitor be- tween Ports 5 and 6, the L1 inductor between Ports 7 and 8, and the C1 capacitor between Ports 9 and 10.
  • Page 13 2.4 GHz RF Matching Design Steps Figure 3.10.a shows the EM simulated impedance of the ladder two-element match at the EFR32 TX pin (Port 2) together with the tar- geted 10 dBm power impedance (~20 + j10 Ω). They are quite close. Here an L0 series inductance of 1.9 nH and a C0 parallel capaci- tance of 1.5 pF is used as shown in the following table.
  • Page 14 Figure 3.12. Measured S11 and S21 (Transfer) Characteristic of the Ladder 2-element SMD Match The measured ladder two- and four-element spectrum plots in the middle of the band (2.45 GHz) with the 7x7 mm dual band EFR32 version is shown in in the first column of Figure 3.13 Measured Spectrum Plots of the Dual Band 7x7 mm EFR32 with (a) a Ladder...
  • Page 15 Appendix 2. 2.4 GHz RF Network Schematics and Technical Data. Figure 3.13. Measured Spectrum Plots of the Dual Band 7x7 mm EFR32 with (a) a Ladder Two-Element Match in 10 dBm Pow- er State and (b) a Ladder Four-Element Match in 20 dBm Power State silabs.com | Building a more connected world.

  • Page 16: Sensitivity Measurements

    AN930: EFR32 2.4 GHz Matching Guide Sensitivity Measurements 4. Sensitivity Measurements The sensitivity of the ladder two-element and four-element matches with the 7x7 mm dual band EFR32MG1 series is compared in the ® table below. Here, 20 byte long standard ZigBee packages are used and 1 % PER sensitivity is shown.
  • Page 17 The power variation is usually less than 0.5 dB, which is less than the chip-to-chip variation. 5. All matches with all EFR32 package versions have less than ~0.5 dB power variation across the entire 2.4 GHz band.
  • Page 18 AN930: EFR32 2.4 GHz Matching Guide References 6. References 1. Christian Gentili: Microwave Amplifiers and Oscillators, McGraw-Hill, 1987, ISBN0-07-022995-3 2. MuRata: http://www.murata.com/products/inductor/chip/feature/rf 3. http://wcalc.sourceforge.net/cgi-bin/coplanar.cgi(Copyright © 2001-2009 Dan McMahill.CGIC, copyright 1996, 1997, 1998, 1999, 2000 by Thomas Boutell and Boutell.Com, Inc.. Permission is granted to use CGIC in any application, commercial or noncommer- cial, at no cost.)
  • Page 19 The optimum impedance here is approximately 20 + j14 Ω. Figure 1.1. Load-Pull Curves and Optimum TX Load Impedances at the 2G4RF_IOP Pin of the Different EFR32 Package Ver- sions: a) 7x7 mm Dual Band, b) 7x7 mm Single Band, c) 5x5 mm Single Band, d) Optimum TX Impedances Shown in One Smith Chart The 2.4 GHz, 20 dBm level optimum termination impedances for the three EFR versions are shown together in D of the above figure.
  • Page 20 AN930: EFR32 2.4 GHz Matching Guide PA Optimum Impedance Determination used, the power variation is less than 0.3 dB. According to this, the selected target impedance for further PA matching design is Zload_opt = ~23 + j11.5 Ω. Further, the optimum impedance does not depend much on the power level. At a power level of 10 dBm, the optimum termination is only slightly off: Zload_opt_10dBm = ~20 + j10.6 Ω...
  • Page 21 AN930: EFR32 2.4 GHz Matching Guide 2.4 GHz RF Network Schematics and Technical Data Appendix 2. 2.4 GHz RF Network Schematics and Technical Data Four 2.4 GHz matching topologies are presented here: • A ladder two-element LC match up to 10 dBm power levels •...
  • Page 22 AN930: EFR32 2.4 GHz Matching Guide 2.4 GHz RF Network Schematics and Technical Data Appendix 2.1 Measured TX Emission The measured TX emissions with the 5 x 5 mm 32-pin package 2.4 GHz EFR version at 2.44 GHz are given in the table below. The tested boards apply a UFL RF connector and a UFL-SMA transition, which together cause approximately 0.5 dB additional attenuation.
  • Page 23 AN930: EFR32 2.4 GHz Matching Guide 2.4 GHz RF Network Schematics and Technical Data Figure 2.1. Power Variations across the Band: (a), (b), (c) Ladder Four-Element Match with the Three EFR Package Versions (d) T-line Match with 7x7 mm Dual Band EFR Version silabs.com | Building a more connected world.

  • Page 24: Appendix 2.2 Rx Sensitivity

    0.5 dB. 5. All matches with all EFR32 package versions has less than ~0.5 dB power variation across the whole 2.4 GHz band. 6. Typical total IC current consumption is ~30 mA at 10 dBm and ~135 mA at 20 dBm power level. For up to 13 dBm power levels, Silicon Laboratories recommends the PA be supplied from the internal dc-dc converter.
  • Page 25 After the optimum termination impedance for the 2G4RF_IOP RF port is determined as Zload_opt = 23+j11.5 Ω in Chapter 2.1 the lad- der four-element 2.4 GHz RF matching design for EFR32 chip has the following steps remaining: 1. Initial design with ideal, loss free elements and without PCB parasitics.
  • Page 26 AN930: EFR32 2.4 GHz Matching Guide 2.4 GHz Ladder 4-element RF Matching Design Steps Appendix 3.2 Design with Parasitics In this step, the PCB and element parasitics and losses are introduced. As with the ladder two-element match design example, the...
  • Page 27 AN930: EFR32 2.4 GHz Matching Guide 2.4 GHz Ladder 4-element RF Matching Design Steps Appendix 3.3 Bench Measurements and Tuning Using the same test setup as in the ladder two-element match (shown in Figure 2.11 in Chapter 2.6), one can tune the macth and acquire the measured S11 and S21 (transfer) characteristics.
  • Page 28 AN930: EFR32 2.4 GHz Matching Guide Transmission Line (Tline) Match for Minimal BOM Solutions (U.S. Patent US9780757B1) Appendix 4. Transmission Line (Tline) Match for Minimal BOM Solutions (U.S. Patent US9780757B1) An alternative low-cost matching technique involves replacing some lumped elements with distributed elements, which saves the cost of the deleted SMD elements.
  • Page 29 The circuit shown in part A of the above figure has a moderate attenuation at the third harmonic frequency. Up to ~13 dBm output power level, this limited third harmonic attenuation is enough for the EFR32 to comply with the ETSI and FCC standards. Therefore, a low BOM two-element match formed by the L0-C0 elements can be used because the transmission line is not required for operation.
  • Page 30 AN930: EFR32 2.4 GHz Matching Guide Transmission Line (Tline) Match for Minimal BOM Solutions (U.S. Patent US9780757B1) Figure 4.3. The Final Tline Match Concept with Real SMD and Transmission Line Elements (PCB Parasitics are Neglected) Figure 4.4. Impedances of Differently Tuned Tline Matches on the 2G4RF_IOP Pins silabs.com | Building a more connected world.
  • Page 31 AN930: EFR32 2.4 GHz Matching Guide Transmission Line (Tline) Match for Minimal BOM Solutions (U.S. Patent US9780757B1) Appendix 4.1 EM Simulations of the Tline Match More accurate tuning can be done with EM simulations. Figure 4.5 EM Simulation of the Tline Match on page 31 part a.
  • Page 32 AN930: EFR32 2.4 GHz Matching Guide Transmission Line (Tline) Match for Minimal BOM Solutions (U.S. Patent US9780757B1) Figure 4.6. Steps 1 and 2 of the Design: Setting C1 to Have Self-Resonance at the Third Harmonic and Setting the Tline Length to Get Good Impedance at the 2G4RF_IOP Pin Figure 4.7.
  • Page 33 Figure 4.8. Measured Characteristic of the Tline Match Given in Above Table Typical measured 10 dBm (with PAVDD fed from DCDC) and 20 dBm spectrum plots with the 7x7 mm 48 pin dual band EFR32 ver- sion, denoted by BRD4151A, in the middle of the band, 2.45 GHz, are shown in Figure 4.11 Measured Spectrum Plots of the Dual Band...
  • Page 34 ~ 20 dBm power levels and below. 3. Different EFR32 package versions can be operated with the same Tline match without a significant effect on the output spectrum. The difference is usually less than 0.5 dB, which is less than the chip-to-chip variation.
  • Page 35 Figure 4.11. Measured Spectrum Plots of the Dual Band EFR32 Version (BRD4151A) with Tline Match at a) 10 dBm Power Level (DCDC on) and with 20 dBm Power Level Figure 4.12. Measured Spectrum Plots of the Single Band EFR32 Versions with Tline Match at 20 dBm Power State a) 7x7 mm (BRD4101A), b) 5x5 mm (BRD4111A) silabs.com | Building a more connected world.
  • Page 36 Trademark Information Silicon Laboratories Inc.® , Silicon Laboratories®, Silicon Labs®, SiLabs® and the Silicon Labs logo®, Bluegiga®, Bluegiga Logo®, Clockbuilder®, CMEMS®, DSPLL®, EFM®, EFM32®, EFR, Ember®, Energy Micro, Energy Micro logo and combinations thereof, "the world’s most energy friendly microcontrollers", Ember®, EZLink®, EZRadio®, EZRadioPRO®, Gecko®, ISOmodem®, Micrium, Precision32®, ProSLIC®, Simplicity Studio®, SiPHY®, Telegesis, the Telegesis Logo®, USBXpress®, Zentri and others are trademarks or registered...