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VCO Design. Z. Dilli, Mar 2012. VCO Design. Adapted from Ryan J. Kier, Low Power PLL Building Blocks , Ph.D. Dissertation, U. of Utah, 2010. System Design. VCO Source follower (external bias) Differential Amplifier (external bias) Inverter chain - PowerPoint PPT Presentation
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VCO Design
Z. Dilli, Mar 2012
VCO Design
Adapted from Ryan J. Kier, Low Power PLL Building Blocks, Ph.D. Dissertation, U. of Utah, 2010.
System Design
• VCO Source follower (external bias) Differential Amplifier (external bias) Inverter chain
• Simulations show a center frequency of around 1 GHz, instead of 433 MHz as designed in the referenced dissertation– No varactor parasitics considered; bias voltage unknown
• Around 4.3% tunability with certain assumptions about inductor parasitics
• Varactor trade-off: Too small reduces tunability range; too large prevents oscillation
VCO-only Outputs
Cvaractor varying from 160 fF (f=1.0737 GHz) to 450 fF (f=1.0385 GHz)Tuning range wider at lower bias currents (affects MOSFET capacitance)
VCO-only Outputs
Ibias changing from <1 mA to >3 mA (by changing Vbias from 1 V to 3 V)
Source-follower and Self-biasing Differential Amplifier
Two source followers for the differential outputs of the VCO, designed not to load the VCO output with excess capacitance
Self-biasing DA increases output swing for the inverter chain operating more reliably
Single-ended output taken out of DA
SF and SBDA operation
Cvaractor=160 fF, f=1.0737 GHz
Inverter Chain
Designed to drive a 1.5 pF load
This is difficult with a full swing with this CMOS technology (0.6 um minimum width) at > 100s of MHz frequencies
Inverter Chain Output to 0.3 pF Load
Inverter Chain Output to 1.5 pF Load
VCO Layout
Full Chip Layout