Frequency Scaling and Topology Comparison of Millimeterwave VCOs

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Frequency Scaling and Topology Comparison of
Millimeter-wave VCOs

• Keith Tang
• Steven Leung
• Nelson Tieu
• Peter Schvan
• Sorin Voinigescu
• University of Toronto, NORTEL

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Outline

• Motivation
• VCO Design Methodology
• Frequency Scaling
• Measurement
• Summary

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Motivation

• MOSFET DC, HF and noise characteristics are
  scalable across technology nodes
• VCO topologies are very simple with one or two
  transistor half-circuits
• Algorithmic design and frequency scaling
  methodologies can be developed even at 77GHz
• ? Design productivity increases!

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Colpitts VCO Design

• Choose LTANK (smallest for low phase noise)
• Calculate Ceq from operating frequency
• Bias transistors at optimum noise current density
  (0.15 mA/mm)
• Size transistors to provide enough negative
  resistance
• Choose LS large (AC open)
• Add RSS, CSS and LSS for bias and noise
  de-coupling

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Cross-coupled VCO Design

• Choose LTANK
• Bias transistors at optimum noise current density
  (0.15 mA/mm)
• Size transistors to provide enough negative
  resistance
• Calculate CVAR from operating frequency

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Frequency Scaling
fOSC
k
Same applies to cross-coupled VCO
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VCO Test Structures
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VCO Test Structures (2)
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10-GHz Colpitts VCO
Tuning range 9.2 10.4 GHz (11.8)
Record phase noise -117.5 dBc/Hz _at_ 1 MHz (100
avg.)
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77-GHz Colpitts VCO
Record tuning range 73.8 80.0 GHz (8.3)
Record phase noise -100.3 dBc/Hz _at_ 1 MHz (100
avg.)
20log(8) 17dB higher than 10-GHz VCOs phase
noise!
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10-GHz Cross-coupled VCO
Tuning range 9.3 10.9 GHz (15.8)
Phase noise -109.2 dBc/Hz _at_ 1 MHz (100 avg.)
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77-GHz CMOSCross-coupled VCOs

• First VCO with p-MOSFET at 77 GHz

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Die Photos

• 77 GHz Colpitts VCO

77 GHz Cross-coupled VCO
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Topology Comparison
At very high frequency
At low frequency
v
v
v v
v X
v
v X
v
v X
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VCO Figure of Merit

• Figure of Merit for VCO defined in ITRS 2003
• But, output power is important for mixer, PA

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FoMs Comparison

• With FoM2, SiGe HBT VCOs show better performance
  than CMOS VCOs at mm-wave frequencies

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Summary

• VCOs with record-breaking performances achieved
  by algorithmic design at 10 and 77 GHz
• Frequency scaling of Colpitts VCOs from 10 to 77
  GHz in 90-nm CMOS, 20 to 40 GHz in 180-nm CMOS
  demonstrated
• First cross-coupled VCO with p-MOSFET at
• 77 GHz
• Colpitts topology exhibits better performances
  than cross-coupled topology at mm-wave
  frequencies

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Acknowledgement

• NORTEL and CMC for fabrication
• CMC for CAD tools
• CFI and OIT for test equipment
• Dr. M. T. Yang for support

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Loss at Very High Frequency

• Considering the transistors resistance
• RG, RS increase with frequency and both lumped to
  RTANK
• Larger transistor size required at very high
  frequencies
• It is critical to keep the VCO layout identical
• Transistor layout
• Component orientation
• Interconnect routing
• such that layout parasitics also scale

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our work