AN437 Si4432 RF P ERFORMANCE A N D FCC C OMPLIAN CE TEST R E S U L TS 1. Introduction This document provides measurement results and FCC compliance results for the Si4432B when operated from 902–928 MHz. The measurement results include receiver sensitivity, adjacent channel selectivity, blocking, transmit output power, transmit output spectrum, transmit deviation, and conducted harmonics. The FCC compliance results demonstrate a full FCC compliance scan to FCC 15.247. All tests are performed using an ISMDK3 kit with a 4432-DKDB1 test card.The Wireless Development Suite (WDS) is used to control the test card. The results can be duplicated by using the same configuration and scripts available on the Silicon Labs website and referenced in the EZRadioPRO Quick Start Guide. All settings were used directly from the Excel Register Calculator worksheet provided on the Silicon Labs website. For measurement results with different RF parameters, contact customer support. Silicon Labs has not attempted to obtain FCC certification on any RF reference design board using Si443x chips. FCC certification is obtained at the module level (and not the chip level), and thus any potential certification that would be obtained on Silicon Labs RF test cards would not be transferable to customer application modules. The compliance test results presented within this application note should be viewed as simply providing confidence to the customer that certification may be obtained, if the recommended RF design and layout practices are followed. 2. Relevant Measurements to comply with FCC FCC compliance in the US only pertains to output power, emissions, and harmonics. There are no receive sensitivity, selectivity or blocking measurements to comply with FCC. Two sections pertain to operation in the 902928 MHz band, 15.247 and 15.249. The maximum output power under FCC 15.247 is +30 dBm with Frequency Hopping Spread Spectrum. FCC 15.249 limits the maximum rms field strength to 50 mV/m at a 3 m distance which is equivalent to a radiated output power of –1.2 dBm EIRP for a non-hopping system. The TX measurements in this report assume a Frequency Hopping System operating at +20 dBm under 15.247. Rev. 0.3 10/12 Copyright © 2012 by Silicon Laboratories AN437 AN437 3. RX Measurement Results 3.1. Sensitivity Sensitivity measurements are done as bit error rate (BER) with BER <0.1%. To convert BER to PER it can be approximated by adding 3 dB (PER = BER+3 dB). A modulation index of H = 1 is used for all cases, with no additional allocation in the IF bandwidth for XTAL tolerance. Sensitivity vs Datarate Sensitivity (dBm) -95 -100 -105 -110 -115 -120 -125 1 10 100 1000 Datarate (kbps) Figure 1. Sensitivity vs. Datarate 3.2. Adjacent Channel Selectivity All selectivity results are done by positioning the input power 3 dB above sensitivity with the primary signal source generator. A second generator with an unmodulated signal is used as the interferer and combined with the primary signal using a power combiner (e.g., Mini-Circuits ZFSC-2-4-S+). The second interferer generator is placed at the desired frequency offset and then the power is increased until the BER degrades to 0.1% (1E-3). For example, the +1 MHz point in Figure 3 shows 62 dB of rejection. The sensitivity for 5 kbps is –116.5 dBm so the primary generator is set to –113.5 dBm. The secondary generator is set 1 MHz away from the primary generator and its power is increased to –51.5 dBm where the BER degrades to 0.1% which results in a rejection of the interferer by 62 dB. 2 Rev. 0.3 AN437 Adjacent Channel Selectivity - 5kbps 0 -10 C/I -20 -30 -40 -50 -60 -70 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 0.8 1 Frequecy Offset (MHz) Figure 2. 5 kbps Adjacent Channel Selectivity Datarate = 5 kbps, Deviation = 2.5 kHz, no allocation in BW for XTAL tolerance. Adjacent Channel Selectivity - 40kbps 20 10 C/I 0 -10 -20 -30 -40 -50 -60 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 Frequency Offset (MHz) Figure 3. 40 kbps Adjacent Channel Selectivity Datarate = 40 kbps, Deviation = 20 kHz, no allocation in BW for XTAL tolerance. Rev. 0.3 3 AN437 3.3. Blocking Blocking measurements are done with the same measurement technique as described above for the adjacent channel selectivity but are performed at larger frequency offsets. C/I Blocking - 5kbps 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 0.01 0.1 1 10 Frequency Offset (MHz) Figure 4. kbps Blocking Datarate = 5 kbps, Deviation = 2.5 kHz, no allocation in BW for XTAL tolerance. \ C/I Blocking - 40kbps 20 10 0 -10 -20 -30 -40 -50 -60 -70 -80 0.01 0.1 1 Frequency Offset (MHz) Figure 5. 40 kbps Blocking Datarate = 40 kbps, Deviation = 20 kHz, no allocation in BW for XTAL tolerance. 4 Rev. 0.3 10 AN437 3.4. Sensitivity vs. Frequency Offset The Sensitivity vs. Frequency Offset measurements are referred to as bucket curves due to the shape of the curve. The receiver and generator frequencies are calibrated for zero frequency offset. The signal generator is then offset and the sensitivity measurement is repeated. The performance for this parameter is directly linked to the programmed receive bandwidth. With AFC disabled there is still internal modem compensation which corrects for offsets up to 0.25 x RX BW and with AFC enabled offsets can be corrected up to 0.35 BW. The modem parameters and receiver bandwidths were set using the Excel Register Calculator worksheet assuming a 20 ppm Crystal Tolerance on both the transmitter and receiver as shown in Figure 6. Figure 6. Excel Register Calculator Worksheet Figure 7 demonstrates the performance for DR = 100 kbps, Dev = 50 kHz, and a BW of 208.4 kHz. For the AFC disabled (modem compensation only) case the frequency offset compensation can be calculated as 0.25 x 208.4 = 52.1 kHz which may be observed in Figure 7. For the AFC enabled case the frequency offset compensation can be calculated as 0.35 x 208.4 = 73 kHz. If more frequency offset compensation is desired then the RX bandwidth should be increased to a value greater than that shown in the Excel Register Calculator worksheet. This may be done by artificially increasing the value used for XTAL Tolerance. Rev. 0.3 5 AN437 Sensitivity vs Frequency Offset - DR=100kbps, BW=208.4kHz -60 Sensitivity (dBm) -70 -80 AFCOFF AFCON -90 -100 -110 -100 -80 -60 -40 -20 0 20 40 60 80 100 Frequency Offset (kHz) Figure 7. Selectivity vs. Frequency Offset, 100 kbps Sensitvity vs Frequency Offset - 40kbps, BW=95.3kHz -60 Sensitivity (dBm) -70 -80 AFCON AFCOFF -90 -100 -110 -50 -40 -30 -20 -10 0 10 20 30 40 Frequenc Offset (kHz) Figure 8. Selectivity vs. Frequency Offset, 40 kbps 6 Rev. 0.3 50 AN437 4. TX Measurements All TX Measurements unless otherwise specified are measured with VDD = 3.3 V, txpow[2:0]=111, frequency = 913 MHz, using the scripts available on the Silicon Labs website and a 4432-DKDB1 test card. All measurements are done at the output of the lowpass filter at the TX SMA connector. The output power is ~1 dB higher at the TX pin of the chip before the lowpass filter. 4.1. Output Power and Spectrum Figure 9. Output Power Rev. 0.3 7 AN437 4.2. Modulated Spectrum Figure 10. Modulated Spectrum—40 kbps/20 kHz Dev 4.3. TX Deviation Figure 11. TX Modulation vs. Time—40 kbps/20 kHz Dev 8 Rev. 0.3 AN437 4.4. TX Output Power Variation vs. VDD and Temperature TX Output Power vs Temp 19.4 19.2 Output Power 19 18.8 18.6 18.4 18.2 18 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 Temp (C) Figure 12. TX Output Power vs. Temperature TX Output Power vs. VDD Output Power (dBm) 20 18 16 14 12 10 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 VDD Voltage Figure 13. TX Output Power vs. VDD Rev. 0.3 9 AN437 TX Output Power vs Power Step TX Output Power (dBm) 20 15 10 5 0 0 1 2 3 4 5 -5 Power Step (txpow[2:0]) Figure 14. TX Output Power vs. Step (txpower[2:0]) 4.5. Conducted Harmonics Figure 15. Conducted Harmonics 10 Rev. 0.3 6 7 AN437 5. FCC Compliance Silicon Labs has tested the Si4432B chip and 4432-DKDB1 TX/RX Split TRX Test Card for FCC Part 15.247 compliance in the 902–928 MHz frequency band, at an output power level of +20 dBm. These FCC compliance tests were performed by Elliott Labs, a FCC certified Electromagnetic Compatibility (EMC) test house. Per FCC Part 15.35, the radiated level of harmonic emissions at frequencies above 1000 MHz are to be measured using an average detector function, and thus there may be some advantage in using a burst-like packet structure rather than continuous transmission. FCC Part 15.35(c) states that if the packet length is less than 100 ms then time averaging can be applied which effectively relaxes the harmonic limits. If the packet structure is longer than 100 ms then time averaging cannot be used. The following test report is for a continuous-wave tone to test to the more stringent case of when a packet is longer than 100 ms. Explicit excerpt from FCC 15.35(c): (c) Unless otherwise specified, e.g.§ 15.255(b), when the radiated emission limits are expressed in terms of the average value of the emission, and pulsed operation is employed, the measurement field strength shall be determined by averaging over one complete pulse train, including blanking intervals, as long as the pulse train does not exceed 0.1 seconds. As an alternative (provided the transmitter operates for longer than 0.1 seconds) or in cases where the pulse train exceeds 0.1 seconds, the measured field strength shall be determined from the average absolute voltage during a 0.1 second interval during which the field strength is at its maximum value. Rev. 0.3 11 AN437 6. 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Revision 0.2 to Revision 0.3 14 Clarified aspects of FCC certification. Rev. 0.3 AN437 NOTES: Rev. 0.3 15 AN437 CONTACT INFORMATION Silicon Laboratories Inc. 400 West Cesar Chavez Austin, Texas 78701 Tel: 1+(512) 416-8500 Fax: 1+(512) 416-9669 Toll Free: 1+(877) 444-3032 Please visit the Silicon Labs Technical Support web page: https://www.silabs.com/support/pages/contacttechnicalsupport.aspx and register to submit a technical support request. Patent Notice Silicon Labs invests in research and development to help our customers differentiate in the market with innovative low-power, small size, analog-intensive mixed-signal solutions. Silicon Labs' extensive patent portfolio is a testament to our unique approach and world-class The information in this document is believed to be accurate in all respects at the time of publication but is subject to change without notice. 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