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Single Balanced Mixer Design ECE 6361

Single Balanced Mixer Design ECE 6361. July 30, 2002 Prof. J. S. Kenney. L01: Group1 Dennis Mahoney Adam Toner Minsik Ahn. Objectives. Single-balanced mixer 2.400-2.485 GHz RF, 2.260-2.345 GHz LO, 140 MHz IF (5 MHz bandwidth) 4-layer PPE printed circuit boards 2.6” by 1.7”

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Single Balanced Mixer Design ECE 6361

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  1. Single Balanced Mixer Design ECE 6361 July 30, 2002 Prof. J. S. Kenney L01: Group1 Dennis Mahoney Adam Toner Minsik Ahn

  2. Objectives • Single-balanced mixer • 2.400-2.485 GHz RF, 2.260-2.345 GHz LO, 140 MHz IF (5 MHz bandwidth) • 4-layer PPE printed circuit boards • 2.6” by 1.7” • Upconversion and downconversion

  3. Description of Design • Balun was realized as a 380 mil long broadside coupled line on layers 1 and 2. • RF was fed into diode through a Wilkinson power divider for balance. • Microstrip stubs were used for reflective terminations.

  4. Alternate Design • Similar design, but balun outputs on single layer • Simulated conversion loss: ~8 dB • Measured conversion loss: ~10.5 dB • Tapered LO input and moved vias in CAD • LO-RF transmission null centered at 2.8 GHz instead of 2.4 GHz indicating poor balun performance • Poor RF port return loss

  5. Simulation • Design, simulation, optimization, and layout in Agilent ADS 2001 • Harmonic balance simulation and optimization with seven harmonics • Curve fit diode for n, Rs; Cj from datasheet

  6. ADS Simulation Model

  7. Wilkinson Power Divider in ADS

  8. ADS Simulation Results: Downconverter

  9. ADS Simulation Results: Upconverter

  10. Mixer Layout

  11. Specifications and Results: Downconverter

  12. Specifications and Results:Upconverter Spurious Response

  13. Measurement Notes • Downconverter conversion loss measured with VNA, accuracy ~0.2 dB • Increased signal generator amplitude to compensate for measured cable loss • Frequency offset mode, calibrated IF output with filter and cables, connected RF directly to test port • Upconverter conversion loss measured with spectrum analyzer, results were better than downconverter but accuracy was ~1 dB • Spurious response measurements with spectrum analyzer set to appropriate RBW and span • Verified IF bandwidth (>> 5 MHz) with swept input, measured output on spectrum analyzer

  14. Problems • Simulated without vias • Vias greatly increased simulation time • Performance margin built into design • One via to ground not drilled • Repaired by drilling, inserting wire, soldering • Top balun trace not centered • Decreases coupling efficiency, increases conversion loss and spurious products • Trace moved in CAD

  15. Problems (continued) • Simulated with straight reactive terminations, fabricated curved stubs • Mixer operating range shifted down in frequency • Conversion loss improved from simulation in low end but increased in high end • Low end spurs increased to out-of-spec from simulation (stub tuning offset down) • Simulated with nominal dielectric constant

  16. Improvements • Increase spacing around stubs to reduce parasitic coupling • Reduce loss in RF input bends • Optimize further in ADS • Limited time for first prototype • Agilent diode improved conversion loss in simulation by ~3 dB • Investigate alternate design problems

  17. Conclusions • Two designs fabricated • One was consistent with simulation • Conversion loss for alternate design was ~3 dB worse than simulation • Primary design met most specifications • Some conversion loss and spurious specs missed • Room for improvement in both designs • Can reduce size and improve performance

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