EE310 Integrated Circuits Seminar, 10/1/02

Ann Guerra guerra at
Thu Sep 26 08:58:53 PDT 2002

EE310 Integrated Circuits Technology and Design Seminar

"Standard CMOS Nonvolatile Reprogrammable Switch for
	Low Phase Noise in LC Oscillators"

		Tamara Papalias
	Dept. of Electrical Engineering
	   San Jose State University

	Tuesday, October 1, 2002
		4:15 p.m.
	Building 380, Room 380X


A nonvolatile reprogrammable switch is characterized in a standard CMOS
process. LC oscillators operating between 1-2GHz utilize the switch to
minimize phase noise deviation over tuning range. Bond wires are
configured as high-quality inductors to achieve low phase noise; tapping
that inductance enhances performance.

Further phase noise improvements target the varactor.  Diodes, the most
common varactor, cause a small deviation in phase noise versus tuning
range. Given the small deviation, phase noise is reported as a single
value.  With the growing popularity of MOS technologies, other varactors
become available.  An accumulation-mode MOS capacitor exhibits a phase
noise deviation similar to the diode varactor.  An inversion-mode MOS
capacitor demonstrates large tuning range but sacrifices phase noise
performance in the middle of the tuning range. Previous LC oscillator
designs with inversion-mode MOS varactors measure phase noise at the limit
of the tuning range where performance is best, and that single value is
reported in accordance with industry practice.  This work investigates
phase noise performance over the entire tuning range where measured phase
noise deviation exceeds 40dB for a 1.25pF inversion-mode MOS varactor.
Instead of a large single varactor, a smaller varactor is utilized with
switchable fixed capacitance.  While an equal tuning range is achieved,
the phase noise deviation is reduced by 30dB.

To obtain a switchable fixed capacitance, a new switch is developed.
Without the advantage of extra process layers, hot electron programming
writes the device in two minutes, ultraviolet exposure erases in twenty
minutes, and a 5nm oxide retains 95% of its charge for fifty years. When
included in an LC oscillator, this switch enables a 42% tuning range at a
center frequency of 1.585GHz using 23.4mW of power in a 0.25um process.
The measured phase noise at 100kHz offset is -90dBc/Hz and the phase noise
deviation is less than 10dB.

The nonvolatile reprogrammable switch also circumvents limitations
associated with use of bond-wire inductances.  Variations in excess of 40%
can be recalibrated post-packaging, ensuring that bond-wires can now be
used repeatably, reliably, and cost-effectively as inductors in standard
CMOS processes.

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