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Mid-Semester Design Review

Mid-Semester Design Review. High Frequency Radio with BPSK Modulation. Goal Statement.

frederica-schulze
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Mid-Semester Design Review

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  1. Mid-Semester Design Review High Frequency Radio with BPSK Modulation

  2. Goal Statement Our project is to design and build a wireless 900 MHz transmitter and receiver for Simply Test, LLC. The transceiver is to conform as closely as possible to the IEEE 802.15.4a standards for Low Rate, Wireless Personal Area Networks (LR-WPAN) and utilize Binary Phase Shift Key (BPSK) modulation.

  3. Deliverables • Working transceiver prototype • Sub-circuit designs for amplifiers and filter • Simulations of sub-circuit designs in PSpice

  4. FunctionalRequirements • Transmit and receive binary data • High carrier frequency • Low power signal transmission • Efficient high frequency PCB layout • Conforms to IEEE 802.15.4a standards for wireless LANs • Transmission range for a conventional wireless network

  5. Specifications • Transmission range of 20 – 30 meters • Antenna and transmission power of 12 dBm • 870-900 MHz carrier frequency • Data throughput of 40kbps

  6. System Block Diagram

  7. Analysis Breakdown • Transmitter • Mixer/Modulation • Power Amplifier • Antennas • Receiver • LNA • Filter • IF Amplifier • Demodulator

  8. Mixer/Modulation • Translation between a high frequency (the RF) and Intermediate Frequency (IF) • The signal is imposed onto a carrier signal so that transmission circuits can be realized on a practical scale • The modulation scheme defines how the signal is imposed onto the carrier signal for transmission

  9. BPSK Modulation • BPSK = Binary Phase Shift Key • Binary 1 represented by 180° phase shift in carrier signal • Binary 0 has no phase shift

  10. Mixer Number of Diodes RF Input Match RF-LO Isolation Conversion Loss Third-Order Intercept Single-Ended 1 Poor Fair Good Fair Balanced (90°) 2 Good Poor Good Fair Balanced (180°) 2 Fair Excellent Good Fair Double Balanced 4 Poor Excellent Excellent Excellent Image Reject 2 or 4 Good Good Good Good Diode Mixers • Provide a simpler topology compared to transistor based mixers • Have a lower noise figure compared to transistor based mixers • Have a higher conversion loss than transistor based mixers

  11. Diode Mixer • Double balanced BPSK Mixer/Modulator

  12. Off-the-shelf Mixer • RF2638 Upconverter/BPSK modulator • Specs:

  13. Important Specs • Third Order Intercept Point, 1 dB Compression • Figures of merit that describe linearity of device • High IP3 desirable • Noise Figure • Noise (in dB) added to amplified signal by amplifier circuitry • Average 1.5 dB for LNA, 5 dB for PA • Input and Output Impedances

  14. Power Amplifier • Boosts the level of the modulated signal for broadcast by the antenna • Operates at the carrier frequency • Need a specific output power level to achieve the 12dBm transmission power specification

  15. Power Amplifier • Linx Technologies BBA-519 • minicircuits.com amplifier selection guide

  16. Antennas • Broadcasts/receives the carrier signal • Considerations: type, size, connector type, and impedance (typically 50 Ohms) • AN-900S RF Antenna from rf-links.com: 896-930 MHz, 3 in. tall, BNC connector, omni Omni-Directional Yagi (directional) Dipole

  17. Low Noise Amplifier • First component of receiving unit • Amplifies weak signal picked up from antenna while contributing minimal noise • Resulting output is sent to mixer

  18. Low Noise Amplifier • Choices from various manufacturers • Input impedance will be properly matched with the antenna for an optimal SWR

  19. Filter • Bandpass filter used to reject unwanted frequency products and pass signals of the selected IF • Important Specs • cutoff frequency/center frequency • passband and stopband • insertion loss • out of band attenuation • VSWR

  20. Filter • Two realization options: One bandpass filter or a low pass filter cascaded with a high pass to create a bandpass filter • Filter selection will depend on selected IF • Possible filter selections:

  21. IF Amplifier • Boosts the level of the filtered IF signal so that it can be accurately demodulated • More options for selection due to operation at the IF rather than the carrier frequency

  22. IF Amplifier • Linx Technologies BBA-322 • High gain version of BBA-519 • minicircuits.com amplifier selection guide also has options

  23. Cost Breakdown • Modulator: $9 • LNA: $4 • Antenna: ? • Power Amp & IF Amp: $2 - $15 • Filter: $2 - $15 • Miscellaneous Components: ? • PCB Board and Manufacturing: ?

  24. Potential Problems • Antenna Selection • Complex design • Physical properties • Impedance matching • Range & frequency considerations • Accounting for mismatches in available components • Power supply requirements for each component

  25. Next Steps • Finalize component selection • Impedance matching • Biasing considerations • Signal level • Order components • Test equipment training • Begin testing components

  26. Schedule • Further component research – Dec. 3rd • Finalized preliminary design – Jan. 17th • Component list • Cost analysis • Finalized system diagram • DFMEA/Design review issue resolution • Place orders for parts – Jan. 21st • Begin PCB layout – Jan. 31st

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