M bius Microsystems MEMS and CMOS Approaches to Monolithic Timing - PowerPoint PPT Presentation

M bius Microsystems MEMS and CMOS Approaches to Monolithic Timing and Frequency Synthesis University of Utah March 28, 2005 Michael S. McCorquodale, Ph.D. Chief Executive and Technology Officer Mobius Microsystems, Inc. Detroit, MI M. S. McCorquodale

M bius Microsystems Overview • An Overview of Timing and Frequency Synthesis • Critical Metrics • Entrenched Technologies • Emerging MEMS Approaches • CMOS Approaches • RF Clock Synthesis for the UMICH-WIMS µ system • Mobius’ Clock Synthesis Technology • Future Work and Summary of Results M. S. McCorquodale 2 of 79

M bius Microsystems An Overview of Timing and Frequency Synthesis M. S. McCorquodale 3 of 79

M bius An Overview of Microsystems Timing and Frequency Synthesis Timing Every synchronous semiconductor component requires a clock to operate Frequency synthesis RF systems require precision frequency references for carrier frequency synthesis Bluetooth/LAN USB Print Server • USB XTAL clock reference • Ethernet XTAL clock reference • Processor XTAL clock reference • Bluetooth radio XTAL reference (on flip side) M. S. McCorquodale 4 of 79

M bius Frequency Synthesis Microsystems Approaches • The phase, delay, or injection locked “bottom-up” approach – Resonator (of some type) serves as a frequency reference – Sustaining oscillator provides a low frequency reference signal – PLL/DLL/ILL multiplies frequency by 2-4096x • Drawbacks with this approach – External components (1 resonator + 2 capacitors) • Expensive, large, pin interface – Reference oscillator required • Either included in PLL or design required – PLL dissipates substantial power to multiply frequency • Particularly true for large multiplication factors – Performance degrades as frequency increases • For multiplication factor N , noise increases by N 2 (to be shown) – Lock and start-up time can be long (e.g. >10,000 cycles) M. S. McCorquodale 5 of 79

M bius Frequency Synthesis Microsystems Approaches • The free-running “direct” approach – RC (phase shift), ring, relaxation oscillators – Designed on-chip for the desired frequency – No external components required (monolithic); No reference • Drawbacks with this approach – Very inaccurate: frequency ±20% untrimmed, ±2% trimmed – Very unstable over power supply & temperature variation: ±2% – High jitter – Typically found in 4-bit microcontrollers M. S. McCorquodale 6 of 79

M bius Frequency Synthesis Microsystems Approaches and Implementations Phase-locked Free-running f ref Nf ref PFD CP LPF f o ÷N Discrete Hybrid Monolithic crystal µ C clock M. S. McCorquodale 7 of 79

M bius Microsystems Critical Metrics M. S. McCorquodale 8 of 79

M bius Summary of Microsystems Critical Metrics • Frequency and time domain metrics – Short-term frequency stability: Jitter and phase noise – Total frequency accuracy: Drift over process, voltage, temperature (PVT), and aging – Rise/fall times – Duty cycle – Start-up time • Environmental conditions – Sensitivity to microphonics, moisture, etc. • Cost – Fabrication process technology – Production trimming requirements – Packaging requirements M. S. McCorquodale 9 of 79

M bius Short-Term Microsystems Frequency Stability v ( t ) V cos t Ideal Oscillator Output = ω o o o v ( t ) ( V ( t )) cos( t ( t )) Noisy Oscillator Output = + ε ω + φ n o o Phase Noise Timing Jitter Power at frequency offset from fundamental Time domain uncertainty in period P v Ideal Period t f f o P v n t 4 t 1 t 2 t 3 t f f o T 1 T 2 T 3 M. S. McCorquodale 10 of 79

M bius Short-Term Microsystems Frequency Stability v Ideal Period Short-Term Timing Jitter Expressions • n -cycle t J ( k ) var( t t ) = − n k n k + • Period (1-cycle) v n J ( k ) var( t t ) var( T ) J = − = = t 1 t 2 t 3 t 4 1 k 1 k k + • Cycle-to-cycle t J ( k ) var( T T ) = − cc k 1 k + T 1 T 2 T 3 Phase Noise Power Spectral Density (PSD) P Power relative to fundamental at offset f m from f o f o +f m ⎛ ⎞ N S ( f f ) + ⎜ ⎟ o v o m = ⎜ ⎟ P P ⎝ ⎠ o o f f f o m M. S. McCorquodale 11 of 79

M bius Frequency Accuracy Microsystems and Precision Nominal frequency acc./prec. f f − • Accuracy is how close the actual actual ref A = frequency is to the desired ( f ref ) f f ref • Precision is how much the maximum f f frequency deviates from the mean − max P f = ( f ), an issue that must be addressed f in production • Will frequency trimming be required? If so, what will it cost (test time) M. S. McCorquodale 12 of 79

M bius Frequency Microsystems Sensitivities or Drift V f • Power supply ∂ f S DD = V f V DD ∂ DD = 1 f ∂ • Temperature TC f f T ∂ G f ∂ S f = • Microphonic G f G ∂ All expressions can be determined by analysis M. S. McCorquodale 13 of 79

M bius Long-Term Microsystems Frequency Stability Long-term frequency stability • A measure of frequency variation over a long period of time • Commonly called aging ∆ f f Long-term instability Short-term instability t M. S. McCorquodale 14 of 79

M bius Microsystems Entrenched Technologies M. S. McCorquodale 15 of 79

M bius Entrenched Microsystems Technologies • Quartz – Piezoelectric bulk acoustic wave (BAW) resonators – ±50 to ±250ppm total accuracy – kHz to 100MHz – Primary applications: frequency and clock synthesis • ZnO – Piezoelectric surface acoustic wave (SAW) resonators – ±100 to ±250ppm total accuracy – 100 to 900MHz – Primary application: IF filters • Ceramic – Ceramic material which is induced to be piezoelectric – ±0.25 to ±5% total accuracy – kHz to 50MHz – Primary application: clock synthesis M. S. McCorquodale 16 of 79

M bius Microsystems Emerging MEMS Approaches M. S. McCorquodale 17 of 79

M bius Two General Microsystems Approaches • Resonator replacements – Utilize micromachining to develop integrated mechanical resonators which can replace discrete resonators – Intended to enable the realization of an integrated time/frequency reference • Improve VCO performance with enhanced passive components – Develop high- Q varactors and inductors in order to realize low phase noise VCOs – Not intended to replace the reference, but related to improving the performance of frequency synthesis blocks (allows Q -factor of reference oscillator to be relaxed) M. S. McCorquodale 18 of 79

M bius Emerging MEMS Microsystems Approaches • Capacitively-coupled microresonators – Surface micromachined poly-Si structures with capacitive actuation • Benefits Clamped-clamped beam poly-Si microresonator – Very high- Q (>10,000) demonstrated [Nguyen, McCorquodale, et al.] • Challenges – High motional resistance (>k Ω ) – Nonlinear transduction causes flicker noise upconversion in oscillator circuits – Specialized packaging required – Process not CMOS-compatible – Frequency trimming required – Moderate temperature coefficient – Microphonic sensitivity may be high Disk poly-Si microresonator [Nguyen, et al.] M. S. McCorquodale 19 of 79

M bius Emerging MEMS Microsystems Approaches Sense Electrode • Piezoelectrically-coupled ZnO Film microresonators Tuning Capacitor – ZnO film couples actuation to surface Drive Electrode micromachined poly-Si beam Device Layer Oxide – Remainder of device identical to Handle Layer previous microresonator Piezoelectric microresonator [Ayazi, et al.] • Benefits – Much lower motional resistance than previous microresonator (~100 Ω ) • Challenges – Same as remaining challenges for previous microresonators M. S. McCorquodale 20 of 79

M bius Emerging MEMS Microsystems Approaches • Piezoelectric film bulk acoustic wave resonators (FBAR) – Similar to an integrated XTAL, but a film Drive Electrode • Benefits – High- Q – Low motional resistance – No specialized packaging required FBAR [Ruby, et al.] Thin • Challenges Piezoelectric – Not CMOS-compatible Film – Accuracy difficult to control • Actually in products Substrate Sense • Best application: multiple Electrodes Piezoelectric Electrode references/filters within one Reflectors package Substrate M. S. McCorquodale 21 of 79

M bius Emerging MEMS Microsystems Approaches • Passive RF MEMS – Micromachined varactors and inductors of various topologies • Benefits – Higher Q than planar passive components and thus lower phase noise in VCOs – Often tunable via mechanical actuation Micromachined parallel plate varactor – Some devices CMOS-compatible [Young, Boser] • Challenges – Most devices not CMOS-compatible – Microphonic sensitivity high for large aspect ratio devices – Some devices not practical for high volume production Micromachined suspended inductor [Yoon] M. S. McCorquodale 22 of 79

M bius Microsystems CMOS Approaches M. S. McCorquodale 23 of 79