Transformer Based Transformer Based OscillatorsOscillators

Adesh GargAdesh Garg

OutlineOutline

Why use a Transformer instead of an Inductor?Why use a Transformer instead of an Inductor? What is a Monolithic Transformer?What is a Monolithic Transformer?

Physical LayoutPhysical Layout Equivalent ModelEquivalent Model Electrical CharacteristicsElectrical Characteristics

Application of Transformers to OscillatorApplication of Transformers to Oscillator Ring OscillatorRing Oscillator LC Tank OscillatorLC Tank Oscillator

ReferencesReferences

Transformers Replacing Transformers Replacing InductorsInductors

Inductors tend to have...Inductors tend to have... Low quality factor (Q) Low quality factor (Q)

Highly LossyHighly Lossy

Lack TunabilityLack Tunability Large amounts of Chip areaLarge amounts of Chip area

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

What is a Monolithic What is a Monolithic Transformer?Transformer?

Physical LayoutPhysical Layout

What is a Monolithic What is a Monolithic Transformer?Transformer?

Equivalent Model [1]Equivalent Model [1]

What is a Monolithic What is a Monolithic Transformer?Transformer?

Electrical CharacteristicsElectrical Characteristics The coupling between stages for typical process The coupling between stages for typical process

is usually between 0.75 < Km < 0.9 [1]is usually between 0.75 < Km < 0.9 [1] Largely dependant on width and spacing of the metal Largely dependant on width and spacing of the metal

tracestraces

Depends on layout and structure. Different Depends on layout and structure. Different benefits for different architecture [1][2]benefits for different architecture [1][2] Coupling, Resonance, Loses, SymmetryCoupling, Resonance, Loses, Symmetry

Background: Types of Background: Types of OscillatorsOscillators

Ring OscillatorRing Oscillator Uses the delay between stages to determine Uses the delay between stages to determine

Oscillator’s frequency (either transmission lines Oscillator’s frequency (either transmission lines or lumped delays).or lumped delays).

LC Tank OscillatorLC Tank Oscillator Uses Inductor and Capacitor to determine Uses Inductor and Capacitor to determine

Oscillator’s frequencyOscillator’s frequency

Ring Oscillator [3]Ring Oscillator [3]

Ring Oscillator Ring Oscillator Inductively TunedInductively Tuned

LC Tank VCO [4]LC Tank VCO [4]

Transformer used to change impedance of Transformer used to change impedance of resonator tank. resonator tank.

Improves Q factor for equivalent inductor of Improves Q factor for equivalent inductor of similar sizesimilar size Phase Noise improvementPhase Noise improvement

LC Tank VCO [4] cont…LC Tank VCO [4] cont…

ConclusionConclusion

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

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

ReferencesReferences

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

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

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

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

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

References cont…References cont…

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

John W. M. Rogers and Calvin Plett, “A 5-ghz radio front-end with automatically Q-tuned 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 notch filter and vco," IEEE J. of Solid State Cir., vol. 38, no. 9, pp. 1547-1554, September 2003.2003.