Oscillators – Electromechanical resonator
Reexamination Certificate
1999-09-21
2001-05-22
Mis, David (Department: 2817)
Oscillators
Electromechanical resonator
C331S1160FE, C331S17700V, C333S186000, C361S278000
Reexamination Certificate
active
06236281
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to resonant microstructures, and more particularly to Q-control for resonant microstructures and electronic filters using such microstructures.
The need for high-frequency bandpass filters with high selectivity for telecommunication systems has stimulated interest in integrated versions of such filters wherein entire systems may be integrated onto a single silicon chip. Examples of systems requiring these filters include radio-frequency (RF) receiver systems, mobile phone networks, and satellite communication systems.
Previously, intermediate frequency (IF) filtering in frequency modulated (FM) receivers has been performed at 10.7 Mega-Hertz (MHz) IF frequency, using highly selective inductive-capacitance (LC) ceramic or crystal filters. Recently, integrated versions using integrated circuit (IC) switched-capacitor techniques have been attempted. However, designs based upon a coupled biquad filter architectures suffer from dynamic range reduction introduced when attempting high-Q operational simulation of LC stages. (Q is a figure of merit equal to reactance divided by resistance. The Q of a system determines the rate of decay of stored energy.) Modulation filtering techniques, such as N-path designs, suffer from the generation of extraneous signals, such as image and clock components inside the signal band, resulting from the remodulation process.
Recent advances in micromachining offer another analog, high frequency, high-Q, tunable integrated filter technology that can enhance filter performance over that of previous integrated versions while maintaining design characteristics appropriate for bulk fabrication in very large-scale integrated (VLSI) systems. Specifically, micromachined mechanical resonators or resonant microstructures may be used. These microresonators are integrated electromechanical devices with frequency selectivity superior to integrated resistance-capacitance (RC) active filtering techniques. Using integrated micromechanical resonators, which have Q-factors in the tens of thousands, microelectromechanical filters with selectivity comparable to macroscopic mechanical and crystal filters may be fabricated on a chip.
Since the passband shape of these filter designs depends strongly on the Q of the constituent resonators, a precise technique for controlling resonator Q is required to optimize the filter passband. Such a Q-control technique would be most convenient and effective if the Q was controllable through a single voltage or an element value, e.g., a resistor, and if the controlled value of Q was independent of the original Q.
An object of the present invention is thus to provide feedback techniques for precise control of the Q-factor of a micromechanical resonator.
Another object of the present invention is to provide very high Q microelectromechanical filters constructed of Q-controlled microresonator biquads in biquad filter architectures. In addition, the invention provides a means for passband correction of spring-coupled or parallel micromechanical resonators via control over the Q-factor of the constituent resonators.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the claims.
SUMMARY OF THE INVENTION
The present invention is directed to a resonator structure. The resonator structure comprises a first electrode at which an input signal may be applied and a second electrode at which an output signal may be sensed. The resonator structure further includes a feedback means for applying the output signal to the first electrode for controlling the Q of the resonator structure.
The equivalent circuit series resistance (R
X
) of the resonator of the present invention is proportional to the inverse of the Q of the resonator. As such, the controlled value of Q is independent of the original Q of the resonator. Rather, it is dependent only on the control voltage (V
Q
) or some other controlling factor such as resistance values.
Additionally, the gain of the resonator (v
0
/v
i
) is equal to the number of input fingers divided by the number of feedback fingers. This is advantageous in that it offers very precise gain values. This enables construction of bandpass biquads with precisely settable gains. Also, the gain will stay constant as the Q is changed.
Dimensions of a microresonator of the present invention may be: a length between about 5 microns (&mgr;m) and 1000 &mgr;m, a width between about 5 &mgr;m and 100 &mgr;m, and a thickness from between about 0.1 and 100 &mgr;m.
High-Q tunable electronic filters based upon the Q-controlled microresonators of the present invention are suitable for batch fabrication using standard complementary metal-oxide semiconductor (CMOS) integrated circuit and micromachining technologies. The Q-controlled microresonators may serve as adjustable biquad stages in various filter architectures such as coupled (or cascaded) biquad, follow-the-leader feedback (FLF), or other multiple-loop feedback techniques. Frequency and bandwidth are independently voltage-controllable. This permits adaptive signal processing.
Noise analysis determines that the dynamic range of a proposed high-Q filter is much higher than that of its high-Q active RC counterparts, i.e., switched-capacitor MOSFET-C, and g
m
-C filters. Specifically, a dynamic range in excess of 90 decibels (dB) is predicted for a filter centered at 10.7 MegaHertz (MHz) with a bandwidth of 56 KiloHertz (kHz).
With the resonators of the present invention, temperature insensitivity can be achieved through micro-oven control, which, on a micron scale, provides orders of magnitude improvement in power dissipation and thermal time constant over equivalent macroscopic methods.
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Howe Roger T.
Nguyen Clark Tu-Cuong
Fish & Richardson P.C.
Mis David
The Regents of the University of California
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