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Transformer Based Oscillators. Adesh Garg. Outline. Why use a Transformer instead of an Inductor? What is a Monolithic Transformer? Physical Layout Equivalent Model Electrical Characteristics Application of Transformers to Oscillator Ring Oscillator LC Tank Oscillator References.

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Presentation Transcript

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Outline

  • Why use a Transformer instead of an Inductor?

  • What is a Monolithic Transformer?

    • Physical Layout

    • Equivalent Model

    • Electrical Characteristics

  • Application of Transformers to Oscillator

    • Ring Oscillator

    • LC Tank Oscillator

  • References


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Transformers Replacing Inductors

  • Inductors tend to have...

    • Low quality factor (Q)

      • Highly Lossy

    • Lack Tunability

    • Large amounts of Chip area

  • Transformers have been used to correct the above short coming [1-5]



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What is a Monolithic Transformer?

  • Equivalent Model [1]


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What is a Monolithic Transformer?

  • Electrical Characteristics

    • The coupling between stages for typical process is usually between 0.75 < Km < 0.9 [1]

      • Largely dependant on width and spacing of the metal traces

    • Depends on layout and structure. Different benefits for different architecture [1][2]

      • Coupling, Resonance, Loses, Symmetry


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Background: Types of Oscillators

  • Ring Oscillator

    • Uses the delay between stages to determine Oscillator’s frequency (either transmission lines or lumped delays).

  • LC Tank Oscillator

    • Uses Inductor and Capacitor to determine Oscillator’s frequency


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Ring Oscillator [3]

  • Ring Oscillator

    • Inductively Tuned


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LC Tank VCO [4]

  • Transformer used to change impedance of resonator tank.

  • Improves Q factor for equivalent inductor of similar size

    • Phase Noise improvement



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Conclusion

  • Transformers are relatively new and their application to tuned circuits have only begin to be explored

  • I expect to see continued research in this field and the use of transformers for RF circuit like the oscillator


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References

  • [1] John Long, “Monolithic transformers for silicon RF IC design," IEEE J. of Solid State Cir., vol. 35, no. 9, pp. 1368-1382, September 2000.

  • [2] Alireza Zolfaghari, Andrew Chan, and Behzad Razavi, “Stacked inductors and transformers in cmos technology," IEEE J. of Solid State Cir., vol. 36, no. 4, pp. 620-628, April 2001.

  • [3] John Long and Raymond Koo, “An inductively-tuned quadrature oscillator with extended frequency control range," in Proceedings of the 2003 International Symposium on Circuits and Systems, 2003, vol. 1, pp. 25-28.

  • [4] Matt Straayer, Jose Cabanillas, and Gabriel Rebeiz, “A low-noise transformer-based 1.7ghz cmos vco," in IEEE International Solid-State Circuits Conference Proceedings, Feb 2002, 17.1.

  • [5] Bogdan Georgescu, Holly Pekau, James Haslett, and John McRory, \Tunable coupled inductor q-enhancement for parallel resonant LC tanks," IEEE Transactions on Circuits and Systems-II: Analog and Digital Signal Processing, vol. 50, no. 10, pp. 705-713, October 2003.


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References cont…

  • John Long and David Cassan, A 1-v transformer-feedback low-noise amplifier for 5-ghz wireless LAN in 0.18um CMOS," IEEE J. of Solid State Cir., vol. 38, no. 3, pp. 427-435, March 2003

  • John W. M. Rogers and Calvin Plett, “A 5-ghz radio front-end with automatically Q-tuned notch filter and vco," IEEE J. of Solid State Cir., vol. 38, no. 9, pp. 1547-1554, September 2003.


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