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