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ECE 6361:Mixer Design Review

ECE 6361:Mixer Design Review. 2.4 GHz Single Balanced Mixer Jan Brosi Vasileios Iliopoulos. Project Objectives I. Project Objectives II. Board:4-layer PPE (1.7x2.6 inches) Schottky diodes: dual series connected. Physical Construction I.

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ECE 6361:Mixer Design Review

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  1. ECE 6361:Mixer Design Review 2.4 GHz Single Balanced Mixer • Jan Brosi • Vasileios Iliopoulos

  2. Project Objectives I

  3. Project Objectives II • Board:4-layer PPE (1.7x2.6 inches) • Schottky diodes: dual series connected

  4. Physical Construction I • Reduced-size rat-race balun with coupled lines on different layers • Radial stubs for matching at RF/LO frequency • Lumped elements for matching at IF and for DC-return 27mm

  5. Physical Construction II • Board parameters: • εr=2.85 ±0.5 • tanδ=0.002-0.003 • core thickness=1mm • resin thickness=50μm • copper thickness=12μm • Diodes: • Zetex ZC2812ECT • IS=9.5nA, RS=16.3Ohm • N=1.27, Cj0=1.1pF • Lumped Elements • Toko 2021 series chip inductors • Panasonic chip capacitors

  6. Model Description & Simulation • Simulation with Agilent ADS using a combination of Multilayer & Microstrip models • Diode Model: ADS P-N diode model with parameters from manufacturer’s data sheet • Inclusion of parasitic elements (bends, steps, T- junctions, vias, pads, parasitics of lumped elements). • Balun design with S-parameter simulation and gradient method optimization for best performance • Mixer harmonic balance simulation with 8 orders and gradient method optimization

  7. Simulation Results • Simulated circuit meets all specs

  8. Conversion Loss Measurement • Measurement of conversion loss in down-conversion using the frequency offset function of HP89441 Network analyzer • The LO port is fed by E4432 Signal Generator with 8.5dBm input power (assuming 0.5 dB cable loss) • Use of a low-pass filter at the input port of the Network analyzer to ensure better phase-locking • The filter response was calibrated out • Accuracy of the measurement: • Signal generator: ± 0.5dB • Network analyzer: ± 0.2dB Total accuracy: ± 0.7dB

  9. Conversion Loss Measurement Results • Conversion loss increases with increasing LO-frequency

  10. Spurious & Isolation Measurement • Measurement of spurious signals and LO-RF isolation for up-conversion using HP8994E Spectrum Analyzer. • Measurement of LO-IF isolation for down-conversion • Sweep over the LO frequency range • Accuracy of the spurious signals measurement • Relative accuracy of spectrum analyzer: ±0.5dB • Accuracy of the LO-RF isolation measurement • Absolute accuracy of spectrum analyzer: ±1dB • Signal generator: ±0.5dB Total accuracy: ± 1.5dB

  11. Spurious & Isolation Measurement Graph LO-IF LO RF LO-2IF LO+2IF LO-3IF LO+3IF LO+4IF

  12. Spurious Measurement Results

  13. Isolation Measurement Results

  14. Changes made to the Circuit • Circuit assembled as designed has bad performance and does not meet any of the specs • Slight change of inductor & capacitor values and interchange of their position increased mixer performance • The mixer seems to be shifted to lower frequencies, it works much better at fLO=1.9 GHz • Thus it was tried to reduce the size of the mixer • Coupled lines were shortened by use of new vias • Line edges were smoothened with copper material to reduce length • Resulting circuit had best performance and was used for measurements

  15. Comparison to Simulations • The measurements don’t match with the simulations • Trying to fit ADS-model to measurements by change of dielectric constant, distance between layers, coupled line offset, length and width of lines, stub length and width, vias and pads, losses and diode model. • This should account for production tolerances and previously not considered effects • Changes didn’t have a significant effect on the simulated mixer performance • Indication that ADS multilayer-model is not accuarate

  16. Summary & Conclusions I • A single-balanced mixer using a reduced-size rat-race balun with mulilayer coupled-lines was designed, simulated, fabricated and measured • Great differences between model and measurements of the produced mixer occurred • Performance could be increased by change of lumped elements and reducing the size of lines • Specifications for Conversion loss are almost met, for Isolation and some spurious signals not • Re-simulation was not successful

  17. Summary & Conclusions II • The ADS multilayer-model does not seem to work well in our case, another software or model should be tried • Board parameters like layer thickness and dielectric constant should be reevaluated • The mixer works much better at lower frequencies, the balun seems to be downshifted • For the next production cycle, the line lengths should be decreased to account for that

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