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Communications Baseband

Communications Baseband. Project 05500. Members. Advisors: Dr. Joe Delorenzo Dr. Eli Saber Dr. Sohail Dianat Team Members: Leland Smith (Team Leader) Jason Riesbeck (Chief Engineer) Jonathan Hutton. Introduction.

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Communications Baseband

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  1. Communications Baseband Project 05500

  2. Members • Advisors: • Dr. Joe Delorenzo • Dr. Eli Saber • Dr. Sohail Dianat • Team Members: • Leland Smith (Team Leader) • Jason Riesbeck (Chief Engineer) • Jonathan Hutton

  3. Introduction • Communications Baseband is a project created by several professors in order to stimulate student’s practical understanding of communication systems. • Sponsor: Rochester Institute of Technology Department of Electrical Engineering

  4. Project Overview • Modulate/Demodulate using Amplitude Modulation, Frequency Modulation, and Pulse Code Modulation • Receive analog or digital transmission approximately a classrooms distance and demodulate • Output original signal to see/hear successful recovery

  5. Team Work Breakdown

  6. Fundamental Design Objectives

  7. Concept Analysis

  8. System Development •Divided into 12 subsystems •Specification developed for each

  9. Feasibility • Assessed at a subsystem level. • Depends on the resources available • To maintain feasibility, subsystems should: • Satisfy design objectives • Economical • Comply with time constraints

  10. FCC Considerations Unlicensed Bands (FCC 15.247.b.4) Antenna gain can be as much as 6dB. All other bands 100mW or less

  11. Audio Subsystem • Block Diagram Input Output

  12. Anti-Aliasing Filter • Specifications: • 0-5V Input • Pass-band 20 kHz • Stop-band 22 kHz • Attenuation 20 dB • Elliptical Filter

  13. Anti-Aliasing Filter Schematic: Plot:

  14. Anti-Aliasing Filter • 6dB Voltage Level = 3dB Power Level = 1.26V • Output =1.26V @ 20.0 kHz • Attenuation =

  15. AM Subassembly • Block Diagrams

  16. AM Modulation • Carrier • 1 MHz Sine Wave • Modulator • Oscillator Input • Audio Input

  17. Carrier Signal • Clock Oscillator • Square Wave • RLC Filter

  18. Carrier Signal

  19. AM Schematic

  20. AM Receiver • AM Receiver • Demodulates Signal • Amplifies the Signal by 18 dB

  21. FM Systems • Complicated to engineer • Could take months in industry Transmitter Receiver

  22. Radio IC’s • A simple and effective solution

  23. Choosing an FM IC

  24. Design Documentation • Schematics • Parts Lists • Specification Documents • Interconnection Control Documents • Test Procedures • Printed Circuit Board

  25. Design Issues • PCB Short

  26. Design Issues • PCB Short • Voltage Regulator Pin-Out

  27. Design Issues • PCB Short • Voltage Regulator Pin-Out • Tuning Capacitor

  28. Design Issues • PCB Short • Voltage Regulator Pin-Out • Tuning Capacitor • Audio Distortion

  29. Design Issues • PCB Short • Voltage Regulator Pin-Out • Tuning Capacitor • Audio Distortion • Tuning Inductor

  30. FM Feasibility

  31. Finished Product FM Transmitter FM Receiver

  32. FSK Systems • Similar to analog FM systems • Also very complicated

  33. FSK Feasibility • Nordic NRF2401 • Transmits data at 1Mbps • 2.4GHz ISM band

  34. FSK Link Analysis • NRF2401 Specification ○ 0dBm output power ○ -80dBm receiver sensitivity • Link Budget Analysis ○ 60dB of attenuation at 10m (with 0dB antenna gain)

  35. Design Documentation • Schematics • Parts Lists • Specification Documents • Interconnection Control Documents • Test Procedures • Printed Circuit Board • FSK Protocol Information

  36. Time Budget

  37. Finished Product

  38. PCM and Control Subassembly • Transmit Side • Conversion of Analog to Digital • Apply Protocol to Digital Data • Manage Memory and Data Flow to FSK Chip • Receive Side • Provide Control to FSK Chip • Receive and Manage FSK Chip Data • Control and Send Data to DAC

  39. Interface Specifications • Rail to rail (0-3.3V) analog signal input • Desire >44 kHz Sample Rate • 1 Mbps transmit rate to FSK chip • Send samples to Digital to Analog Converter at sample rate

  40. Solutions • PICmicro Microcontroller • Analog Devices DAC • 10-bit • No overhead bits • Serial • Up to 20 MHz data rate

  41. Capabilities • PIC offers 10-bit AD • PIC provides I/O ports • USART (Synchronous/Asynchronous Communications), and MSSP (Master Synchronous Serial Port for DAC) • Many I/O Ports for control lines • Provides 1MHz USART • Data storage and management

  42. Chosen Microprocessor • PIC18LF2525 • Low voltage at full speed 3.3V @ 32MHz • Internal oscillator up to 32MHz • External interrupts • MSSP • More robust commands

  43. System Diagram

  44. RX FSK-PIC-DAC Interface • Vref = Vdd

  45. Communications Protocol • PIC must manage data from 10-bit samples to exact 1 Mbps output • USART sends 8-bit words and takes care of data rate • The FSK chip offers several protocol options

  46. IN  PIC  OUT • Known: What goes in must come out – and at the same rate. • Therefore: The rate the PIC can sample at is governed by the FSK communications protocol. • Sampling rate must be some integer number of the outgoing packet rate

  47. Protocol Options

  48. Synchronous with Shockburst Option

  49. Asynchronous Option 1

  50. Asynchronous Option 2

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