APPLICATION NOTE Atmel AT02785: Low-Cost RF Module with Dipole Antenna Atmel Wireless Features • • • • • • • • • Low-cost RF module design ZigBee®, IEEE®802.15.4 or 6LoWpan Single layer PCB Folded dipole antenna Minimal component count Spartan design JTAG interface 20 GPIO pins Supports ATmega SoC RF devices Description This application note features a minimalist low-cost RF module design. This design uses a folded dipole antenna and is implemented on a single layer Printed Circuit Board (PCB). This design eliminates baluns and chip antennas to reduce cost. This design uses common 100 mil through-hole headers to access 20 GPIO pins and a JTAG programming header. This design can be used with Atmel® ATmega RF System-on-Chip (SoC) wireless microcontrollers in QFN-64 packages including the Atmel ATmega128RFA1 and the Atmel ATmega RFR2 Series. 42133A−WIRELESS−05/2013 Table of Contents 1. Introduction .......................................................................................... 3 2. Folded Dipole Antenna ........................................................................ 4 3. IO Connections .................................................................................... 6 4. RF Grounding ...................................................................................... 6 5. Metal Shield and 32kHz Clock ............................................................. 7 6. Support for Other ATmega Parts ......................................................... 7 7. Warnings .............................................................................................. 7 7.1 ESD Advisory .................................................................................................... 7 7.2 Avoid metal near antenna ................................................................................. 7 7.3 EMI filtering, fusing and clamping ..................................................................... 7 7.4 Stacks ............................................................................................................... 7 8. Schematics .......................................................................................... 8 9. BOM ….. .......................................................................................... 9 10. Gerbers ….. ........................................................................................ 10 11. Revision History ................................................................................. 11 Atmel AT02785: Low-Cost RF Module with Dipole Antenna [APPLICATION NOTE] 42133A−WIRELESS−05/2013 2 1. Introduction Many situations require the lowest cost possible for hardware design. This design was optimized for low cost by using PCB antenna without a balun. The layout was designed to be implemented on a single layer PCB for further cost reduction. This design includes the minimum parts necessary to get on the air with an Atmel ATmega RF SoC. Figure 1-1. Folded Dipole Module. Atmel AT02785: Low-Cost RF Module with Dipole Antenna [APPLICATION NOTE] 42133A−WIRELESS−05/2013 3 2. Folded Dipole Antenna The Folded Dipole Antenna is a classic pattern that provides sufficient radiation for general purpose applications. The dipole antenna can take direct input from the ATmega’s balanced RF ports and does not need a balun. Matching and filtering are implemented with low-cost discrete components to further reduce Bill of Materials (BOM) costs. Antenna radiations patters are shown below. Dipole antennas have good gain in the Y-Z plane normal to the antenna. In the X-Y plane, dipole antennas have a spindle torus shape and exhibit nulls near the axis. Figure 2-1. Side Radioation Pattern Y-Z Plane. Atmel AT02785: Low-Cost RF Module with Dipole Antenna [APPLICATION NOTE] 42133A−WIRELESS−05/2013 4 Figure 2-2. Flat Radiation Pattern X-Y Plane. Atmel AT02785: Low-Cost RF Module with Dipole Antenna [APPLICATION NOTE] 42133A−WIRELESS−05/2013 5 3. IO Connections The Dipole Module has 20 GPIO pins that are available to the user. These are arranged in two simple 1x10 100 mil through-hole headers. The I/O pins were selected for access to popular features and direct routing to the IC. System designers can top-load or bottom-load the headers as they choose. It is recommended to make contact with all the DGND signals if the underlying base-board has a ground plane. This will increase the effective area of the ground plane. Table 3-1. Header Pin GPIO Pin Assignment. SOC Pin Function Header Pin SOC Pin Function J1.01 DGND J2.01 DGND J1.02 DGND J2.02 VDD J1.03 U1.25 PD0-SCL J2.03 U1.64 PF1-ADC1 J1.04 U1.26 PD1-SDA J2.04 U1.63 PF0-ADC0 J1.05 U1.27 PD2-RXD1 J2.05 U1.62 AREF J1.06 U1.28 PD3-TXD1 J2.06 U1.58 AGND J1.07 U1.36 PB0-SS* J2.07 U1.47 PE1-TXD0 J1.08 U1.37 PB1-SCLK J2.08 U1.46 PE0-RXD0 J1.09 U1.38 PB2-MOSI J2.09 U1.43 PB7-OC0A J1.10 U1.39 PB3-MISOI J2.10 U1.42 PB6-OC0B Table 3-2. JTAG Pin Assignment. Header Pin SOC Pin Function J3.01 U1.03 TCK J3.02 J3.03 DGND U1.05 J3.04 TDO VDD J3.05 U1.04 TMS J3.06 U1.12 RESET* J3.07 VDD J3.08 N/C J3.09 U1.06 J3.10 TDI DGND The JTAG signals are routed to a 2x5 100 mil header that is compatible with Atmel standard JTAG/ICE connections. These connections are correct for top-side loading of the JTAG header. System designers can invert this header, or route to a base-board but be aware this can result in a mirror image layout that may not work with standard programming devices. 4. RF Grounding RF systems work much better with a good ground plane. The dipole antenna is differential and self contained. It is less dependent on RF grounding than monopole styles; however, a ground plane will help with consistent performance. If the base-board includes a ground plane connecting to this plane with the DGND pins is recommended. Try to avoid common impedance coupling of electrical currents through the module. Atmel AT02785: Low-Cost RF Module with Dipole Antenna [APPLICATION NOTE] 42133A−WIRELESS−05/2013 6 5. Metal Shield and 32kHz Clock This layout was designed for mounting a metal shield. This shield is not required for laboratory operation. This shield may, or may-not, be required for different markets and different types of regulatory certification. Consult with a certified compliance laboratory for details on metal shield usage. The 32.768kHz crystal is used by the CPU for deep sleep modes. Use of this crystal is optional. 6. Support for Other ATmega Parts At the time this paper was written, this layout works with all known Atmel Wireless SoCs in 64-Pin QFNs. This antenna is designed for 2.4GHz operation only. The U1 footprint is compatible with the following: • • • • Atmel ATmega128RFA1 Atmel ATmega256RFR2 Atmel ATmega128RFR2 Atmel ATmega64RFR2 7. Warnings 7.1 ESD Advisory This module is designed with minimal superfluous circuitry. Be advised this module does not have any Electrostatic Discharge (ESD) protection except the IC’s built-in ESD diodes. System designers and technicians handling these modules need to be aware for the risks of ESD damage and take appropriate precautions in risky applications. 7.2 Avoid metal near antenna DO NOT put ground planes, power planes, signal traces, metal letters or metal symbols, metal paint or metal screws, nuts or washers, directly under the dipole antenna. 7.3 EMI filtering, fusing and clamping These modules do not have Electromagnetic Interference (EMI) filtering, fusing or over-voltage protection. In harsh applications the system designer may need to add these features for extra safety and reliability. 7.4 Stacks The Dipole module can be used with all known software stacks from Atmel. This includes: • • • • • • ZigBee BitCloud® ZigBee RF4CE ZigBee Light Link IEEE802.15.4 MAC 6LoWPAN Atmel Proprietary Light Weight Mesh By convention some software stacks may need supporting hardware such as ID-PROMS, persistent memories, binding stimulus or indicators. These are not included in this module design. Atmel AT02785: Low-Cost RF Module with Dipole Antenna [APPLICATION NOTE] 42133A−WIRELESS−05/2013 7 8. Schematics Atmel AT02785: Low-Cost RF Module with Dipole Antenna [APPLICATION NOTE] 42133A−WIRELESS−05/2013 8 9. BOM Description Designator Footprint Qty Manufact MPN Cap. cer. NP C1 0402 0 Cap. cer. 3pF C2 0402 1 MURATA GJM 1555C1HR30BB01D DIGIKEY 490-3079-2-ND Cap. cer. 82pF C3, C4 0402 2 MURATA GJM 1555C1H8R2CB01D DIGIKEY 490-3110-2-ND Cap. cer. 1pF C5 0402 1 MURATA GJM 1555C1H1R0CB01D DIGIKEY 490-3083-2-ND Cap. cer. 7pF C6 0402 1 MURATA GJM 1555C1HR70BB01D DIGIKEY 490-6079-2-ND Cap. cer. 15pF C7, C8, C12, C13 0603 4 MURATA GRM 1885C1H120JA01D DIGIKEY 490-1405-2-ND Cap. cer. 15pF C9, C10, C11, C14 0603 4 MURATA GRM 188R61A105KA61D DIGIKEY 490-1543-2-ND Header, 10-pin J1, J2 HDR1X10 2 SAMTEC TSW-110-05-T-S DIGIKEY SAM 1019-10-ND Header, 5-pin, dual row J3 HDR2X5 1 SAMTEC TSW-105-05-T-D DIGIKEY SAM-1018-05-ND 2.7nH L1, L2 0402 2 MURATA LQG15HN2N7S02D DIGIKEY 490-1078-2-ND 1.0nH L3, L4 0402 2 MURATA LQG15HN1N0S02D DIGIKEY 490-1073-2-ND Res 10kΩ 1/10W 1% 0603 SMD R1 0603 1 GENERIC DIGIKEY P10.0KHCT-ND Res 0.0Ω 1/10W 0603 SMD R2, R4 0603 2 GENERIC DIGIKEY P0.0GCT-ND Res 0.0Ω 1/4W 1206 SMD R3, R5 1206 2 GENERIC DIGIKEY P0.0ECT-ND Header, 16-pin, right angle SH1 SHIELD_BM I-S-103_LAIRD 1 LAIRD BMI-S-103 DIGIKEY 903-1008-1-ND U1 QFN64 1 Atmel ATMEGA128RFA1-ZU DIGIKEY ATMEGA128RFA1-ZU-ND Crystal 32.768kHz 12.5pF SMD X1 3.2x1.4mm 1 ABRACON ABS07-32.768KHZ-T DIGIKEY 535-9542-1-ND Crystal 16MHz 8pF SMD X2 3.2x2.5mm 1 ABRACON ABM 8-16.000MHZ-10-1-U-T DIGIKEY 535-9675-1-ND 802.15.4 compliant AVR receiver ® Vendor VPN Atmel AT02785: Low-Cost RF Module with Dipole Antenna [APPLICATION NOTE] 42133A−WIRELESS−05/2013 9 10. Gerbers Atmel AT02785: Low-Cost RF Module with Dipole Antenna [APPLICATION NOTE] 42133A−WIRELESS−05/2013 10 11. Revision History Doc. Rev. Date Comments 42133A 05/2013 Initial document release Atmel AT02785: Low-Cost RF Module with Dipole Antenna [APPLICATION NOTE] 42133A−WIRELESS−05/2013 11 Atmel Corporation Atmel Asia Limited Atmel Munich GmbH Atmel Japan G.K. 1600 Technology Drive Unit 01-5 & 16, 19F Business Campus 16F Shin-Osaki Kangyo Building San Jose, CA 95110 BEA Tower, Millennium City 5 Parkring 4 1-6-4 Osaki, Shinagawa-ku USA 418 Kwun Tong Road D-85748 Garching b. Munich Tokyo 141-0032 Tel: (+1)(408) 441-0311 Kwun Tong, Kowloon GERMANY JAPAN Fax: (+1)(408) 487-2600 HONG KONG Tel: (+49) 89-31970-0 Tel: (+81)(3) 6417-0300 www.atmel.com Tel: (+852) 2245-6100 Fax: (+49) 89-3194621 Fax: (+81)(3) 6417-0370 Fax: (+852) 2722-1369 © 2013 Atmel Corporation. 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