AN4315 Application note BAL-NRF02D3 matched balun with integrated harmonics filter for Nordic Semiconductor chips with ultralow power transceivers Introduction The nRF51422-CEAA and nRF51822-CEAA from Nordic Semiconductor are 2.45 GHz combo chips with an ultralow power transceiver. The BAL-NRF02D3 from STMicroelectronics is an ultraminiature balun for which the matching impedance has been customized for the nRF51422-CEAA, and nRF51822-CEAA Nordic Semiconductor circuits. The BAL-NRF02D3 integrates matching network and harmonics filters. It uses STMicroelectronics’ IPD technology on non-conductive glass substrate which optimizes RF performance. The BAL-NRF02D3 has been tested and approved by Nordic Semiconductor on the PCA10018 nRFgo module.The BAL-NRF02D3 demonstrates a higher system performance compared to traditional solutions. This document presents the test and performance results. September 2013 DocID024845 Rev 1 1/10 www.st.com Test and performances 1 AN4315 Test and performances Figure 1. BAL-NRF02D3 reference design from Nordic Semiconductor nRF51822-CEAA (WLCSP) C1 12pF C2 X1 16MHz 12pF P0.29 P0.28 P0.27 P0.26 P0.25 P0.24 P0.23 P0.22 P0.21 C8 100nF C7 B7 A8 A7 C5 A6 B6 B5 A5 A4 A3 A2 VCC_nRF VCC_nRF VDD DCC P0.30 P0.31 P0.00 P0.01 P0.02 P0.03 P0.04 P0.05 P0.06 P0.07 VDD AVDD VSS VSS VSS ANT2 ANT1 VDD_PA DEC2 P0.20 P0.19 P0.18 P0.17 nRF51822 P0.08 P0.09 P0.10 P0.11 P0.12 P0.13 P0.14 P0.15 P0.16 SWDIO SWDCLK B1 B4 J8 J7 H6 J6 J5 H5 H4 J4 J3 J2 H2 C8 H3 C11 100nF B8 B9 D8 E8 C9 E9 D9 F9 F8 H9 G8 H7 H8 VSS VSS P0.08 P0.09 P0.10 P0.11 P0.12 P0.13 P0.14 P0.15 P0.16 SWDIO/nRESET SWDCLK VSS VSS C7 100nF P0.30 P0.31 P0.00 P0.01 P0.02 P0.03 P0.04 P0.05 P0.06 P0.07 C9 1.0nF P0.29 P0.28 P0.27 P0.26 P0.25 P0.24 P0.23 P0.22 P0.21 DEC1 XC2 XC1 VCC_nRF A1 G6 G9 D7 C1 D1 E1 F1 G1 F2 H1 G2 B1 B3 A3 A2 P0.20 P0.19 P0.18 P0.17 ANT2 SE ANT1 VDD_PA GND A1 RF B1 BAL-NRF02D3 C10 47nF C3 2.2nF U1 nRF51822-CEAA R1 12k Using BAL-NRF02D3 no external components are required for matching and for harmonic filtering. Only a 2.2 nF external capacitor is required for VDD decoupling. Figure 2. PCA10018 ST balun reference nRFgo module from Nordic Semiconductor 2/10 DocID024845 Rev 1 AN4315 2 Benefits of BAL-NRF02D3 reference design Benefits of BAL-NRF02D3 reference design The BAL-NRF02D3 provides two essential benefits: Decrease in the BOM count by 80%, from 5 components to 1 component More than 80% PCB area reduction compared to the original design with the BAL-NRF01D3 and discrete components Compared to discrete solutions, the BAL-NRF02D3 solution is much easier to implement. Thanks to this smart implementation: No RF measurement tools and RF skills are required to design and validate the function. Performance is less sensitive to component placement. PCB design is symmetrical from differential output to antenna, providing much shorter traces between transceiver outputs to the balun. As a result, ST BAL-NRF02D3 reduces harmonics generation. DocID024845 Rev 1 3/10 Measured performances AN4315 3 Measured performances 3.1 Nordic Semiconductor PCA10018 nRFgo module (nRF51822-CEAA) The results presented in this section are based on measurements performed with the PCA10018 nRFgo module and the BAL-NRF02D3. The BAL-NRF02D3 balun offers high suppression of 2nd to 4th harmonics and simplifies implementation of nRF51822 WLCSP as regards FCC and ETSI compliance tests. Table 1. Main parameter compensated measurements (2402 to 2480 MHz) Parameter Values Parameter PA_TX_FUND (0 dBm) (low) 0.56 PA_TX_2H (4 dBm) -49.4 PA_TX_FUND (0 dBm) (mid) 0.85 PA_TX_3H (0 dBm) -53.8 PA_TX_FUND (0 dBm) (high) 1.28 PA_TX_3H (4 dBm) -41.7 PA_TX_FUND (4 dBm) (low) 4.18 PA_TX_4H (0 dBm) -61.8 PA_TX_FUND (4 dBm) (mid) 4.2 PA_TX_4H (4 dBm) -56.0 PA_TX_FUND (4 dBm) (high) 4.55 LO (0 dBm) -60.3 PA_TX_2H (0 dBm) -40.9 Receiver sensitivity [dBm] -90.1 Figure 3. Output power carrier in 4dBm mode (not compensated) 4/10 Values DocID024845 Rev 1 AN4315 Measured performances Figure 4. Second harmonic in 4dBm mode (not compensated) Figure 5. Third harmonic in 4dBm mode (not compensated) DocID024845 Rev 1 5/10 Measured performances AN4315 Figure 6. Fourth harmonic in 4dBm mode (not compensated) Figure 7. Receiver local oscillator leakage (RX_LO) in 4dBm mode (not compensated) 6/10 DocID024845 Rev 1 AN4315 Layout recommendations for nRF51822 and nRF51422 Figure 8. BAL-NRF02D3 land pattern metrics Top layer pad Ø = 220 µm 650 µm Soldermask opening Ø = 320 µm 3.2 Measured performances Figure 9. PCB stack-up recommendation 35um 230um 35um 9 30um 35um 230um 35um DocID024845 Rev 1 7/10 Measured performances AN4315 Figure 10. More layout information at Nordic Semiconductor’s web site 8/10 DocID024845 Rev 1 AN4315 4 Ordering information Ordering information Table 2. Ordering information 5 Part number Marking Weight Base Qty Delivery mode BAL-NRF02D3 SC 1.82 mg 5000 Tape and reel Revision history Table 3. Document revision history Date Revision 05-Sep-2013 1 Changes Initial release. DocID024845 Rev 1 9/10 AN4315 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no liability whatsoever relating to the choice, selection or use of the ST products and services described herein. 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