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Transformer Based Oscillators

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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Transformer Based Oscillators

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  1. Transformer Based Oscillators Adesh Garg

  2. 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

  3. 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]

  4. What is a Monolithic Transformer? • Physical Layout

  5. What is a Monolithic Transformer? • Equivalent Model [1]

  6. 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

  7. 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

  8. Ring Oscillator [3] • Ring Oscillator • Inductively Tuned

  9. LC Tank VCO [4] • Transformer used to change impedance of resonator tank. • Improves Q factor for equivalent inductor of similar size • Phase Noise improvement

  10. LC Tank VCO [4] cont…

  11. 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

  12. 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.

  13. 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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