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Low-Noise Dielectric Resonator Oscillator

Low-Noise Dielectric Resonator Oscillator. Design Frequency of 4.26 GHz. Introduction. Group Background Radio Frequency Circuit Design Microwave Frequency Circuit Design Origin of Project Suggested by Prof. Feng of High Speed Integrated Circuits Group. Objective.

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Low-Noise Dielectric Resonator Oscillator

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  1. Low-Noise Dielectric Resonator Oscillator Design Frequency of 4.26 GHz

  2. Introduction • Group Background • Radio Frequency Circuit Design • Microwave Frequency Circuit Design • Origin of Project • Suggested by Prof. Feng of High Speed Integrated Circuits Group

  3. Objective • Dielectric Resonator Oscillator (DRO) • High frequency • Low phase noise • Purpose of DRO • Digital clock source • Current Issues • Jitter at very high frequencies

  4. Objective • Advantages of DRO • Frequency stability • Tunable • High Quality factor (20,000 at 10 GHz) • Dielectric resonator minimizes noise • Low construction cost

  5. Design

  6. Characterization of 50 Ohm Microstrip Line • Copper Board Parameters: • Substrate : Ultralam • Line Parameters (after calibration): • L = 7.62 cm • W = 0.43 cm

  7. Characterization of Dielectric Resonator • Utilization of Aluminum Casing for Measurement of Resonator • Measured Resonant Frequency : • f = 4.26 GHz • De-embed Measured Data

  8. DC Bias Stub • Calculation of Bias Stub Lengths

  9. DC Bias Stub • We want Zin to appear as an open circuit,

  10. DC Bias Stub • Utilize ADS for Stub Length Optimization • DC Stub Capacitors = • DC Blocking Capacitors =

  11. DC Bias Circuit • Active Bias Circuit establishes operating point for the transistor • PNP Transistor (Q1): 2N3906 Vbe = -0.75V , b1 = 100 • RF NPN Transistor (Q2): MRF571 Vce = 10V , b2 = 80

  12. DC Bias Circuit Design • Specification • Vcc = 15V, Vce(Q2) =7V , Ic(Q2) =60mA

  13. Characterization of Transistor • Obtain S-parameters using Network Analyzer

  14. Negative Resistance Criteria for Oscillation • One-port negative resistance model

  15. Optimization of Zin • Simulation Results

  16. Optimization of Zin • Network Analyzer • Check at the Design Frequency, f=4.26 GHz

  17. Optimization of Zin • Measured Results

  18. Single Stub Matching Network • Smith Chart • accounts for Negative Resistance for Oscillation

  19. Single Stub Matching Network Design • b= 1.92 • B = 1.92 / 50 Ohms = 0.0384 • jB = (1/Zos)(tan ((2pLstub)/ leff)) • Zos = 46.17 Ohms ( from ADS) • Lstub = 0.1682 l • l = 4.95 cm • Lstub = 8.3 mm • d= 0.4822 – 0.3142 = 0.168 l = 8.3 mm

  20. Functionality Tests • Spectrum Analyzer • Checking for Oscillation and Phase Noise

  21. Challenges and Solutions • Challenge: • DC blocking Capacitors on Microstrip Line • At very high frequencies, Capacitors look inductive • Solution: • Tried to couple the line * Tried 39pF Capacitors

  22. Challenges and Solutions • Challenge: • DC Bias Circuit / Transistor with Gain • Problems with finding a suitable transistor with gain • Solution: • Rebuilt DC Bias Circuit to give more current * Chose Transistor with larger , MRF571.

  23. Challenges and Solutions

  24. Challenges and Solutions • Challenge: • Emitter Stub Length • Had trouble figuring out how to find emitter stub length for negative resistance • Solution: • Tried Trial and Error Method by starting with 2.6mm and cutting 2mm at a time to try to find optimal length and checked for stability in ADS. * Figured out how to use ADS variable optimization

  25. Challenges and Solutions • Challenge: • Transistor Burnout • One of the two transistors apparently burned out while operating • Smelled something burning and checked current which ended up being 2.4 mA vs. 56 mA • Solution : • First replaced DC Bias circuit transistor and found that it was okay * Second replaced the RF Transistor.

  26. Verification Methods • ADS Simulations • Between each step, ADS was used to simulate the circuit to find out if it would work ideally for that particular section of the circuit • In many cases, the simulations aided in finding problems that could have been potentially disastrous if we had built the board first

  27. Recommendations • Use ADS to simulate your plan of action. • Measure each components parameters. • Make sure the Transistor is bias at the correct operating point to supply enough gain for oscillation to occur. • Take Design Frequency into account at all times ( i.e., capacitors are high frequencies behave as inductors).

  28. Fine

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