APPLICATION NOTE nRF904 RF and antenna layout Q$1 *HQHUDO Gerber files for RF layouts have been made for Nordic VLSI’s Q5) Single Chip 915MHz RF Transmitter [1]. A loop antenna for 915MHz has 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 UHDGPHZUL 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. 5)OD\RXWIRUQ5) The RF layouts include all necessary circuitry to design the radio frequency part of a short range communication system based on Q5). The transmitter data and control lines DIN, XO8, PWR_DOWN, and CLOCK/ASK, 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. 'LIIHUHQWLDOFRQQHFWLRQWRORRSDQWHQQD 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 layout 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 layout must be connected exactly to the corresponding connection points numbered 1, 2 and 3 on the RF layout. The Gerber files Zip archive filename is 3&%BQ5)BGLII]LS. The recommended external components are as given in Table 1. Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway 3DJHRI - Phone +47 72 89 89 00 - Fax +47 72 89 89 89 November 2001 APPLICATION NOTE Q5)5)DQGDQWHQQDOD\RXW &RPSRQHQW C1 C2 C3 C4 C5 C6 C7 R1 R2 R3 R4 R5 X1 'HVFULSWLRQ NP0 ceramic chip capacitor (REXT pin decoupling) X7R ceramic chip capacitor (REXT pin decoupling) X7R ceramic chip capacitor (Supply decoupling) NP0 ceramic chip capacitor (Supply decoupling) NP0 ceramic chip capacitor (Supply decoupling) Tantalum chip capacitor (Supply decoupling) X7R ceramic chip capacitor (Data bit stream filter) 0.1W chip resistor (Crystal oscillator bias) 0.1W chip resistor (Transmitter power setting) 0.1W chip resistor (XO8 output level setting) 0.1W chip resistor (Data bit stream filter/Frequency deviation setting) 0.1W chip resistor (Data bit stream filter/Frequency deviation setting) Crystal 6L]H 9DOXH 0603 33 7ROHUDQFH pF 0603 4.7 nF 0603 4.7 nF 0603 33 pF 0603 33 pF 3216 4.7 µF 0603 680 pF 0603 150 kΩ 0603 47 1) kΩ 0603 15 2) kΩ 0603 22 3) kΩ 0603 3.9 4) kΩ - 14.2992 5) Table 1 Recommended External Components. 1), 2), 3), 4), 5) See [1]. 6LQJOHHQGHGFRQQHFWLRQWR:DQWHQQDE\XVLQJDGLIIHUHQWLDOWRVLQJOH HQGHGPDWFKLQJQHWZRUN 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. The antenna connection point should be as close as possible to the output of the matching network. If this is not possible of practical reasons, the PCB track between the output of the matching network and the antenna connection should be carried out as a 50Ω microstrip line. In such a case, the length of the microstrip line is limited to a few centimetres. For a standard FR4 printed circuit board with 1.54mm substrate thickness and relative dielectric constant εr ≈ 4.25 at 915MHz, the width of the microstrip line should be 3mm. The Gerber files Zip archive filename is 3&%BQ5)BVLQJOHBQHWZ]LS. The recommended external components are as given in Table 1, with addition of the components in the differential to single ended matching network as given in Table 2. Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway 3DJHRI - Phone +47 72 89 89 00 - Fax +47 72 89 89 89 November 2001 8QLWV MHz APPLICATION NOTE Q5)5)DQGDQWHQQDOD\RXW &RPSRQHQW C8 C9 R6 L1 L2 'HVFULSWLRQ NP0 ceramic chip capacitor (Impedance matching) NP0 ceramic chip capacitor (Impedance matching) 0.1W chip resistor (Impedance matching) Chip inductor, SRF>915 MHz 6) (Impedance matching) Chip inductor, SRF>915 MHz 7) (Impedance matching) 6L]H 9DOXH 7ROHUDQFH 8QLWV 0603 3.3 <±0.1 pF 0603 3.3 <±0.1 pF 0603 1 0603 68 ±5% nH 0603 15 ±2% nH kΩ Table 2 Recommended components in the differential to single ended matching network 6), 7) See [1]. Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway 3DJHRI - Phone +47 72 89 89 00 - Fax +47 72 89 89 89 November 2001 APPLICATION NOTE Q5)5)DQGDQWHQQDOD\RXW aaaaaaaa VDD + C6 4.7uF 3216 R1 150k 0603 PWR_DOWN aaaaaaaa CLOCK/ASK R2 47K 0603 DIN C2 4.7nF 0603 C3 4.7nF 0603 R5 3.9K R4 22K 0603 0603 Loop antenna connection U1 1 2 3 4 XO8 C1 33pF 0603 X1 14.2992MHz R3 15K 0603 C4 33pF 0603 XTAL REXT XO8 VDD VSS ANT1 ANT2 DIN 8 7 6 5 1 3 2 C5 33pF aaaaaaaa 0603 nRF904 915MHz Single chip RF Transmitter SOIC 8 C7 680pF 0603 aaaaaaaa 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 3DJHRI - Phone +47 72 89 89 00 - Fax +47 72 89 89 89 November 2001 APPLICATION NOTE Q5)5)DQGDQWHQQDOD\RXW aaaaaaaa VDD VDD + C6 4.7uF 3216 C5 33pF 0603 R1 150k 0603 R6 1K 0603 PWR_DOWN CLOCK/ASK DIN C2 4.7nF 0603 C3 4.7nF 0603 R5 3.9K R4 22K 0603 0603 C8 RF out 50 ohm xxxxxx U1 1 2 3 4 XO8 C1 33pF 0603 X1 14.2992MHz R3 15K 0603 R2 47K 0603 aaaaaaaa L1 68nH 0603 XTAL REXT XO8 VDD 8 7 6 5 VSS ANT1 ANT2 DIN L2 15nH 0603 3.3pF 0603 C9 nRF904 915MHz Single chip RF Transmitter C4 SOIC 8 33pF 0603 3.3pF 0603 C7 680pF 0603 aaaaaaaa 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 3DJHRI - Phone +47 72 89 89 00 - Fax +47 72 89 89 89 November 2001 APPLICATION NOTE Q5)5)DQGDQWHQQDOD\RXW /RRSDQWHQQDOD\RXWV A loop antenna with T-match [2] is a good solution for low cost and small size radio modules. A layout solution for a small rectangular loop antenna is described below. Figure 5 shows the basic geometry of the designed rectangular loop antenna. a1 C1 C2 C3 RQ a2 d/2 d/2 3 1 2 Figure 5. Geometry of rectangular loop antenna The loop antenna physical parameters are D = loop antenna length [mm] D = loop antenna width [mm] G = feed length [mm] E= width of loop conductor The antenna is tuned to a resonance frequency of 915MHz with chip capacitors & & and &. To keep the variations in antenna gain due to capacitor variations lower than 3dB and thus achieve reproducible values of antenna gain in mass production, the total tuning capacitance tolerance should not exceed 5% (that is, ±2.5%). According to [2], the antenna should then be designed for a Q-value of about 40. For the designed loop antenna, capacitors && and & should have tolerances equal to or better than ±0.1pF. The resistor 54 controls the 4-value of the antenna. The loop antenna is tuned to approximately 300Ω with a T-match. The width of the loop conductor is 1.524mm (60mil). There is no ground plane beneath the antenna. Table 3 shows a summary of the designed loop antenna. /RRS DQWHQQD D[D >PP@ )HHG OHQJWK G >PP@ 9.5x9.5 13 & 9DOXH 7ROHUDQFH >S)@ >S)@ 3.3 ±0.1 & 9DOXH 7ROHUDQFH >S)@ >S)@ 3.9 & 9DOXH 7ROHUDQFH >S)@ >S)@ ±0.1 6.8 ±0.1 54 >N:@ 4 YDOXH =R >:@ 18 40 300 Table 3 Summary of the loop antenna 8) Thick film chip resistor with resistance tolerance 5% or better. Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway 3DJHRI - Phone +47 72 89 89 00 - Fax +47 72 89 89 89 November 2001 APPLICATION NOTE Q5)5)DQGDQWHQQDOD\RXW The component values given in Table 3 are only valid when the connection points numbered 1, 2 and 3 on the loop antenna layout, as shown in Figure 6, are connected exactly to the corresponding connection points numbered 1, 2 and 3 on the RF layout with differential loop antenna connection. The component footprints used in the loop antenna layout are size 0603. The layout of the rest of the communication system may influence the antenna tuning and require measurement of the antenna together with the complete system in order to find the values for C1, C2, C3 and RQ for your system. Figure 6. Loop antenna PCB layout (not actual size) It is recommended that a system should not be designed with a longer communication range than the application requires. Estimations on communication range with the antenna presented in this application note and a receiver with a given sensitivity and antenna gain, can be made based on the theory given in [2]. Initial communication range tests should be carried out with the lowest RF output power setting that, based on the estimations, satisfies the range requirements. If the achieved communication range does not satisfy the requirements, the RF output power should be increased to the required level. Table 4 lists the Gerber file Zip archive filename for the antenna layout. /RRSDQWHQQD D[D >PP@ *HUEHUILOHV=LSDUFKLYHILOHQDPH 9.5x9.5 Loop_9.5x9.5mm_915MHz.zip Table 4 Gerber files Zip archive filenames Measured loop antenna gain relative to λ/4 dipole antenna mounted on a 40x40cm ground plane is shown in Table 5. /RRSDQWHQQD D[D >PP@ *DLQUHODWLYHWROGLSROH DQWHQQD >G%@ 9.5x9.5 -15 Table 5 Measured loop antenna gain relative to λ/4 dipole antenna mounted on a 40x40cm ground plane Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway 3DJHRI - Phone +47 72 89 89 00 - Fax +47 72 89 89 89 November 2001 APPLICATION NOTE Q5)5)DQGDQWHQQDOD\RXW 5HIHUHQFHV 1. Product SpecificationQ5), “Single Chip 915MHz Transmitter”, Nordic VLSI ASA. 2. Application note Q$1, “Small loop antennas”, Nordic VLSI ASA. Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway 3DJHRI - Phone +47 72 89 89 00 - Fax +47 72 89 89 89 November 2001 APPLICATION NOTE Q5)5)DQGDQWHQQDOD\RXW /,$%,/,7<',6&/$,0(5 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. /,)(6833257$33/,&$7,216 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 : 08.11.2001. Application Note order code : 081101-nAN900-03 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 3DJHRI - Phone +47 72 89 89 00 - Fax +47 72 89 89 89 November 2001 APPLICATION NOTE Q5)5)DQGDQWHQQDOD\RXW <285127(6 Nordic VLSI ASA Revision: 1.1 - Vestre Rosten 81, N-7075 Tiller, Norway 3DJHRI - Phone +47 72 89 89 00 - Fax +47 72 89 89 89 November 2001 APPLICATION NOTE Q5)5)DQGDQWHQQDOD\RXW 1RUGLF9/6,:RUOG:LGH'LVWULEXWRUV )RU<RXUQHDUHVWGHDOHUSOHDVHVHHKWWSZZZQYOVLQR 0DLQ2IILFH Vestre Rosten 81, N-7075 Tiller, Norway Phone: +47 72 89 89 00, Fax: +47 72 89 89 89 (PDLOQ5)#QYOVLQR 9LVLWWKH1RUGLF9/6,$6$ZHEVLWHDWKWWSZZZQYOVLQR Revision: 1.1 3DJHRI November 2001