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CC11xx Range Improvements

This presentation discusses the existing range and current consumption of CC11xx devices and proposes improvements through new RF network designs. The effects of antenna impedance and load conditions on range are considered, along with the test results and conclusions.

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CC11xx Range Improvements

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  1. CC11xx Range Improvements Richard Wallace

  2. Presentation Abstract • Presentation Abstract • Abbreviations • General • NE1 Antenna • NE2 Antenna • SS2 Antenna • Out of the Box Experience • Existing range of CC11xx • Current Consumption • CC1101 868/915 Reference Design Schematic • Abstracts from DN017 - CC11xx 868/915 MHz RF Matching • Effects of non-50ohm wideband load - Antenna Impedance • Improvement Goals • Calculated Expected Range for 915MHz, CC1101 • New RF Network Designs • Discrete Solutions • SAW Filter Solution • Johanson Filter-Balun Solution • Range Test Results • Best Results Obtained • Results from initial Conclusion from Range Measurements • Test Results - Current Consumption • Test Result Matrix • Conclusions • Extra Slides

  3. Abbreviations - General CC11xx CC1100, CC1101, CC1110, CC1111 and CC1150 TX Transmitter RX Receiver bps bits per second PER Packet Error Rate BOMa Existing reference design (CC1110) BOMb Johanson Filter-balun design (CC1101) BOMc Existing reference design (CC1101) BOMc1 Extra filtering discrete balun design (CC1101) BOMc_saw Existing reference design (CC1101) np not performed

  4. Abbreviations – NE1 Antenna

  5. Abbreviations – NE2 Antenna

  6. Abbreviations – SS2 Antenna (yellow)

  7. Existing range of CC11xx – Out of the Box Experience What range do we have today ?

  8. Existing range of CC11xx – Out of the Box Experience Area of Improvement #1: Range between 2 units implementing CC11xx is not good enough and the performance can be improved

  9. Variation of Current Consumption - Out of the Box Experience CC1101; 915MHz, simple unmodulated TX carrier; 10dBm, all values are in mA “close” measurements are close proximity to the antenna Area of Improvement #2: The design is sensitive due to antenna / load conditions.Large current consumption difference depending on the load.

  10. CC1101 - 868/915 Reference Design Schematic Balanced LPF for matching and reflecting harmonics. 50Ohm 3 pole LPF Balun (LPF/HPF) DC block EM revisions: rev3.2 - latest with 3 pole LPF rev3.1 - 2 pole LPF (L123, C123) low supression of 2nd harm for 3- 7dBm output power. rev2.2 - Obsolete - radiation emission problems (does not have any balanced LPF) Differential impedance as seen from the RF-port (RF_P and RF_N) towards the antenna is 86.5 + j43@ 868 MHz.

  11. CC1101 - 868/915 Reference Design Schematic – Abstracts from DN017 An ideal output signal from the CC11xx products in TX mode is a square wave signal at the RF_P and RF_N pins and a sine wave at the antenna port. To achieve this, the filterbalun must reflect the harmonics back towards the RF_P and RF_N ports. The shape of the square wave pulse depends on the impedance at the different harmonics. The current consumption in TX depends on the shape of the signal at RF_P and RF_N. Lowest possible current consumption is achieved by having the odd harmonics (3rd and 5th) reflected back. Square wave output from chip (TX).

  12. CC1101 - 868/915 Reference Design Schematic – Abstracts from DN017 Unexpected high current consumption in a design may be caused by incorrect or missing reflection of harmonics. The simplest way of reflecting the harmonics towards the chip is to have a differential low pass filter between the CC11xx and the balun. Ideally the series inductors, L121 and L131, will reflect harmonics towards the chips with high real part of the impedance. The low pass filter will also lower the harmonics level into the balun and reducing the risk of having unwanted radiated power through the balun and the single ended filter. Square wave output from chip (TX).

  13. Effects of non-50ohm wideband load - Antenna Impedance All RF equipment have a wideband impedance of 50 ohms so good measurements results are obtained since the design can be optimised for the wideband load of 50ohms. However, antennas are normally adapted to 50ohms at their operating frequency but the impedance at the harmonics is not 50ohms. Depending on the antenna impedance at the harmonic frequencies; different results can be obtained from vendor to vendor since the reflected signal to the chip is distorting the square wave output due to phase change. Ideally, the load should be capable of a mismatch and the output from the chip should not be effected. Distorted square wave output from chip (TX). Impedance unknown at harmonic frequencies for most antenna vendors.

  14. Area of Improvement #1: Out of box experience is poor since the range between 2 units implementing CC11xx is not good enough. Area of Improvement #2: Improve the reference design so that the design is not so sensitive on the load conditions. Improvement Goals

  15. CC1101 Expected Range – 915MHz Expected Range with perfect match: 915MHz: 360m

  16. New RF Network Designs The following RF network concepts will be tested to see if the range can be further improved and the load variation sensitivity can be reduced: • Discrete Solution • Existing discrete solution (BOMc) • Extra filtering Discrete Balun Solution (BOMc1) • SAW Filter Solution • existing discrete balun + SAW filter (BOMc_saw) • Murata balun + SAW filter (BOM_board_2a) • Chip Filter Balun (Johanson) Solution (BOMb)

  17. New RF Network Designs - Discrete Solutions Existing discrete solution (BOMc) Extra Filtering Discrete Balun Solution (BOMc1) • Two extra series inductors • LPF can be reduced for cost reductions

  18. New RF Network Designs - Discrete Solutions • Original BOM attenuates the second harmonic by 28dB (BOMc) • BOMc1 with extra filtering components uses two additonal inductors to give additional filtering to achieve a larger attenuation of the second harmonic; expected attenuation is 50dB

  19. New RF Network Designs – SAW Filter Solution • High Insertion loss • Outstanding supression of spurious and harmonics • Small physical size (1x1.4mm)

  20. New RF Network Designs – SAW Filter Solution existing discrete balun + SAW filter (BOMc_saw) Murata balun + SAW filter (BOM_board_2a) • 22nH Shunt inductor • LDB21869M20C Standard Murata Balun • SAFEB915MAL0F00 SAW Filter • BOMc • SAFEB915MAL0F00 SAW Filter • LPF can be removed

  21. New RF Network Designs – Johanson Filter-Balun Solution (BOMb) Johanson Filter balun (BOMb) • Only 2 components required !

  22. New RF Network Designs – Johanson Filter-Balun Solution (BOMb) Simulations from Johanson Balun

  23. Range Test Results

  24. Best Results Obtained from Range Test Measurements

  25. Conclusions from Range Measurements • CC1101 compared to CC1110 has a greater range of 21% to 23% depending on antenna. • Both CC1110 & CC1101 showed a range improvement of 41% when the antenna was changed from the standard NE1 antenna to the dipole NE2 antenna. • SS2 antenna is best suited for the discrete solution. Better performance than NE2. • Caluclated range of approx 360m should be expected with 0dBm, 915MHz & 250kbps. • CC1101 has as good range as CC1000 for the same sensitivity. • NE1 antenna must be changed asap in the kit to NE2 or SS2. • With a Johansson balun the distance was increased by 32% to 35% depending on antenna used on the CC1101 setup. • Best results are with the NE2 antenna and Johnson balun solution so far. • NE2 antenna is best suited for the Johanson balun solution

  26. Test Results - Current Consumption – Effects of SAW filter can be compared with the figures highlighted in yellow

  27. Test Result Matrix • Cost estimation include pick & place assembly cost, only RF network is included

  28. Cost Calculations • All the prices are based upon information from the component vendors: • 0.002 USD 0402 Murata Capacitor (COG, pF) • 0.007 USD Multi-Layer 0402 Murata Inductor • 0.049 USD Wire-Wound 0402 Murata Inductor • 0.070 USD Murata Balun (500k/year) • 0.160 USD Johanson Filter-Balun (500k / year) • 0.190 USD Johanson Filter-Balun (50k / year) • 0.250 USD Murata SAW Filter (500k/year) • 0.300 USD Murata SAW Filter (500k/year) • 0.030 USD Pick & Place Assembly Cost (per component)

  29. Conclusions New application in-designs: • Discrete Solution: • Lowest component cost, good range, but susceptible to load changes • Extra filtering solution only improved load susceptibility slightly, no range improvement compared to standard discrete solution (at the moment). • SAW filter Solution: • with discrete balun: highest cost, good range, not susceptible to load variations • with Murata balun: low total cost, good range, not susceptible to load variations and compact solution • Johanson Filter-Balun Solution: • Lowest total cost, best range, not least susceptible to load variations, best all-round solution. • Only two components, minor risk for in-design errors • Out of box Experience - Evaluation Kit: • New Antenna (NE2 or SS2) will be replacing old antenna (NE1); range improvement of >41% with new antenna.

  30. Extra Slides - Current Consumption

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