APPLICATION NOTE nRF402 RF and antenna layout 1. nAN400-06 General Gerber files for RF layouts have been made for Nordic VLSI’s nRF402 Single Chip 433MHz RF Transmitter [1]. Three different loop antennas for 433MHz have also been made available. The Gerber files for each layout are compressed into the Zip archive format. The Zip archive files includes a file named readme.wri that must be read before importing the Gerber files into the PCB editor. All described layouts should be fabricated on standard 1.6mm double-sided FR4 printed circuit board. 2. RF layout for nRF402 The RF layouts include all necessary circuitry to design the radio frequency part of a short range communication system based on nRF402. The transmitter data and control lines DIN, CS and PWR_UP are available at the perimeter of the RF layout and should be connected to the digital part of a customer’s application. +3V and GND are also available at the perimeter of the RF layout. The +3V for the RF part of the application circuit should be filtered separately from the supply voltages of any digital circuitry. Star routing is strictly recommended from the +3V supply source to the RF, digital or other parts of the application circuit. All RF layouts presented below are equal except for the antenna connection circuitry. Solutions for differential connection to loop antenna and single ended connection to 50Ω antenna are presented. 2.1. Differential connection to loop antenna Figure 1 shows the schematics for RF layout with differential connection to a loop antenna. The PCB layout is shown in Figure 2. The loop antenna layouts described in chapter 3 can easily be placed together with this RF layout. The connection points numbered 1, 2 and 3 on the loop antenna layouts should be connected exactly to the corresponding connection points numbered 1, 2 and 3 on the RF layout. If the loop antenna of practical reasons has to be connected further away from the nRF402, the connection has to be symmetrical and the length of the PCB tracks must not exceed about 6cm. Since the loop antenna is a tuned antenna, the tuning of the antenna has to be checked in this case. The Gerber files Zip archive filename is PCB_nRF402_diff.zip. Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway Page 1 of 10 Phone +47 72 89 89 00 - Fax +47 72 89 89 89 February 2000 APPLICATION NOTE nRF402 RF and antenna layout The recommended external components are as given in Table 1. Component C1 C2 C3 C4 C5 C6 L1 R1 R3 X1 Description NP0 ceramic chip capacitor, (Crystal oscillator) NP0 ceramic chip capacitor, (Crystal oscillator) X7R ceramic chip capacitor, (Supply decoupling) NP0 ceramic chip capacitor, (Supply decoupling) X7R ceramic chip capacitor, (Supply decoupling) NP0 ceramic chip capacitor, (Supply decoupling) VCO inductor, Q>45 @ 433 MHz 1/8W chip resistor, (Crystal oscillator) 1/8W chip resistor, (Transmitter power setting) Crystal Size Value 0603 0603 0603 0603 1206 0603 0603 0603 0603 - 22 22 4.7 100 2.2 100 22 1.0 221) 4.000 Tolerance ±2% 2) Units pF pF nF pF µF pF nH MΩ kΩ MHz Table 1 Recommended External Components. 1) 2) See [1]. See [1]. Single ended connection to 50Ω Ω antenna by using a differential to single ended matching network Figure 3 shows the schematics for RF layout with single ended connection to 50Ω antenna by using a differential to single ended matching network. The PCB layout is shown in Figure 4. 2.2. The antenna connection point should be as close as possible to the output of the matching network. If the PCB track between the output of the matching network and the antenna connection point of practical reasons has to exceed about 3cm, this track should be carried out as a 50Ω microstrip line. For a standard FR4 printed circuit board with 1.54mm substrate thickness and relative dielectric constant εr ≈ 4.45 at 433MHz, the width of the microstrip line should be 3mm. The Gerber files Zip archive filename is PCB_nRF402_single_netw-1_1.zip. The recommended external components are as given in Table 1, except for the supply decoupling capacitor C6, with addition of the components in the differential to single ended matching network as given in Table 2. Component C6 C7 C8 C9 L2 L3 L4 L5 Description X7R ceramic chip capacitor, (Supply decoupling) NP0 ceramic chip capacitor NP0 ceramic chip capacitor NP0 ceramic chip capacitor Chip inductor, SRF>433 MHz3) Chip inductor, Q>45 @ 433 MHz Chip inductor, Q>45 @ 433 MHz Chip inductor Size Value 0603 0603 0603 0603 0603 0603 0603 0603 1 1.8 470 1.5 180 22 22 22 Tolerance <±0.25 <±0.1 ±10% ±2% ±2% ±2% Table 2 Recommended components in the differential to single ended matching network 3) See [1]. Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway Page 2 of 10 Phone +47 72 89 89 00 - Fax +47 72 89 89 89 February 2000 Units nF pF pF pF nH nH nH nH APPLICATION NOTE nRF402 RF and antenna layout +3V R1 1M 0603 C5 2.2uF 1206 C1 22pF 0603 X1 4.000 MHz C2 22pF 0603 REFERENCE U1 L1 22nH 0603 C3 4.7nF 0603 C4 100pF 0603 CS 1 2 3 4 5 6 7 XC1 VSS VDD VCO1 VCO2 LPF CS XC2 PWR_UP VSS ANT1 ANT2 DIN RF_PWR 14 13 12 11 10 9 8 PWR_UP Loop antenna connection aaaaaaaa 1 3 2 DIN C6 100pF 0603 nRF402 433MHz Single chip RF Transmitter SSOIC14 R3 22K 0603 Figure 1. Schematics for RF layout with differential connection to a loop antenna Top silk screen Bottom silk screen Top view Bottom view Figure 2. RF layout with differential connection to a loop antenna Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway Page 3 of 10 Phone +47 72 89 89 00 - Fax +47 72 89 89 89 February 2000 APPLICATION NOTE nRF402 RF and antenna layout +3V R1 1M 0603 C5 2.2uF 1206 C1 22pF 0603 X1 4.000 MHz C2 22pF 0603 REFERENCE L3 22nH 0603 U1 L1 22nH 0603 C3 4.7nF 0603 CS 1 2 3 4 5 6 7 XC1 VSS VDD VCO1 VCO2 LPF CS XC2 PWR_UP VSS ANT1 ANT2 DIN RF_PWR 14 13 12 11 10 9 8 C8 RF out 50 ohm PWR_UP DIN aaaaaaaa 470pF 0603 C7 1.8pF 0603 C9 1.5pF 0603 +3V nRF402 433MHz Single chip RF Transmitter SSOIC14 C4 100pF 0603 L2 180nH 0603 R3 22K 0603 L4 0603 22nH L5 22nH 0603 C6 1nF 0603 Figure 3. Schematics for RF layout with single ended connection to 50Ω antenna by using a differential to single ended matching network Top silk screen Bottom silk screen Top view Bottom view Figure 4. RF layout with single ended connection to 50Ω antenna by using a differential to single ended matching network Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway Page 4 of 10 Phone +47 72 89 89 00 - Fax +47 72 89 89 89 February 2000 APPLICATION NOTE nRF402 RF and antenna layout 3. Loop antenna layouts A loop antenna with T-match [2] is a good solution for low cost and small size radio modules. Three different layout solutions for small rectangular loop antennas are described below. Figure 5 shows the geometry of the designed rectangular loop antennas. a1 C1 C2 RQ a2 d 3 1 2 Figure 5. Geometry of rectangular loop antenna The loop antenna physical parameters are a1 a2 d b = loop antenna length [mm] = loop antenna width [mm] = feed length [mm] = width of loop conductor Each antenna is tuned to a resonance frequency of 433MHz with chip capacitors C1 and C2. For the designed loop antennas, these capacitors should have tolerances better then 5%. The resistor RQ controls the Q-value of the antenna. All loop antennas are tuned to approximately 400Ω with a T-match. The width of the loop conductor for all of the loop antennas is 1mm. There is no ground plane beneath the antennas. Table 3 shows a summary of the designed loop antennas. Loop antenna a1 x a2 [mm] Feed length d [mm] 18x10 25x15 35x20 22 21.5 22.5 Value [pF] C1 Tolerance [pF] 5.6 3.3 1.8 ±0.25 ±0.1 ±0.1 RQ4) [kΩ Ω] Q-value Value [pF] C2 Tolerance [pF] Zo [Ω Ω] 10 5.6 4.7 ±0.25 ±0.25 ±0.1 18 18 68 55 55 68 400 400 380 Table 3 Summary of the loop antennas 4) Thick film chip resistor with resistance tolerance 5% or better. Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway Page 5 of 10 Phone +47 72 89 89 00 - Fax +47 72 89 89 89 February 2000 APPLICATION NOTE nRF402 RF and antenna layout Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway Page 6 of 10 Phone +47 72 89 89 00 - Fax +47 72 89 89 89 February 2000 APPLICATION NOTE nRF402 RF and antenna layout 4. References 1. Product Specification nRF402, “433MHz Single Chip RF Transmitter”, Nordic VLSI ASA. 2. Application note nAN400-03, “Small loop antennas”, Nordic VLSI ASA. Revision: 1.1 Page of February 2000 APPLICATION NOTE nRF402 RF and antenna layout LIABILITY DISCLAIMER Nordic VLSI ASA reserves the right to make changes without further notice to the product to improve reliability, function or design. Nordic VLSI does not assume any liability arising out of the application or use of any product or circuits described herein. LIFE SUPPORT APPLICATIONS These products are not designed for use in life support appliances, devices, or systems where malfunction of these products can reasonably be expected to result in personal injury. Nordic VLSI ASA customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify Nordic VLSI ASA for any damages resulting from such improper use or sale. Application Note. Revision Date : 29.02.2000. Application Note order code : 290200-nAN400-06 All rights reserved ®. Reproduction in whole or in part is prohibited without the prior written permission of the copyright holder. Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway Page 8 of 10 Phone +47 72 89 89 00 - Fax +47 72 89 89 89 February 2000 APPLICATION NOTE YOUR NOTES Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway 9 10 Phone +47 72 89 89 00 - Fax +47 72 89 89 89 February 2000 APPLICATION NOTE Nordic VLSI - World Wide Distributors Main Office: Vestre Rosten 81, N-7075 Tiller, Norway Phone: +47 72 89 89 E-mail: [email protected] Visit the Nordic VLSI ASA website at http://www.nvlsi.no