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Low Phase Noise Oscillators

for MEMS inductors

Sofia Vatti

Christos Papavassiliou

2

Summary

Two sets of oscillator circuits prototyped for EPSRC-STEP FASTSAN:• Fixed frequency single phase Oscillators for MEMS integration• Voltage controlled Oscillators for MEMS integration• Quadrature Oscillators for MEMS integration • MEMS characterisation test patterns• Same circuits with planar inductors provided by the process

Extensive on-chip calibration facilities:• MEMS inductor characterisation pattern• Monolithic inductor characterisation pattern• RF wafer probe calibration structures

All oscillator circuits ESD protected

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Measurements on “chip2” (novel VCO, AMS 0.35)

Proposed topology:- oscillates at 1.952 GHz- phase noise as State of the Art- extra tunability through internal

loop supply (+varactors)

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measurements - 1: frequency tuning

Varactor control: 100 MHz

Reference Supply Control: VDD2

30 MHz tunability ---- linearity improved

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measurements – 2 phase noise

Varactor control

Reference Supply Control: VDD2

- Phase Noise performance maintained when tuning via VDD2.- Integrated inductor Q=3 @ 2GHz (low compared to literature)

- Power consumption = 50mW (high compared to literature)

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FastSAN “chip 3”micrograph

MEMS Inductor Integration pad

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Oscillator exampleDC probe card (10 needles) :

Power & frequency band switching

RF probes

Calibration patterns

UMC 0.18 micron CMOS

200um

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VCO Measurements: circuit

- No varactors in the tank

- Control voltages switch in caps C0-C4 to change frequency bands

- 3nH foundry inductor

Breaking the loop with Caps provides access to gates of NMOS. AC is still coupled.

DC gate bias is set from M3-M5, M4-M6, by controlling VDD2.

VDD2 control from 0.8V-1.8V provides up to 300MHz tuning.

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VCO measurements: tuning range

VCO Tuning Range

3.8003.9004.0004.1004.2004.3004.4004.5004.6004.7004.8004.9005.0005.1005.2005.3005.400

0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00

VDD2 (V)

Fre

qu

ency

(G

Hz)

- 1.5GHz total range: 3.8 to 5.3 GHz

- Switch-in capacitor approach

- 5 coarse-tuning regions

- Fine tuning (200 to 300MHz) provided by bias mechanism

- No varactors used

Reference Supply Control

Gradually switching in the caps: 5 switches

Phase noise: <-70dBc/Hz @100kHz

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Conclusions

• Collaboration with OSD Group• CAS role:

– Electronic Design for CMOS – MEMS co-integration– Novel LC oscillator topologies have been prototyped and tested– Performance comparable to state of the art

• OSD role:– Develop Hetero-Integration Technology

• Project status:– Final stages of CMOS+MEMS assembly