U.S. patent application number 14/633885 was filed with the patent office on 2015-07-02 for noise reduction in mems oscillators and related apparatus and methods.
This patent application is currently assigned to Sand 9, Inc.. The applicant listed for this patent is Sand 9, Inc.. Invention is credited to Pritiraj Mohanty.
Application Number | 20150188488 14/633885 |
Document ID | / |
Family ID | 49913500 |
Filed Date | 2015-07-02 |
United States Patent
Application |
20150188488 |
Kind Code |
A1 |
Mohanty; Pritiraj |
July 2, 2015 |
NOISE REDUCTION IN MEMS OSCILLATORS AND RELATED APPARATUS AND
METHODS
Abstract
Mechanical resonating structures are used to generate signals
having a target frequency with low noise. The mechanical resonating
structures may generate output signals containing multiple
frequencies which may be suitably combined with one or more
additional signals to generate the target frequency with low noise.
The mechanical resonating structures may be used to form
oscillators.
Inventors: |
Mohanty; Pritiraj; (Los
Angeles, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sand 9, Inc. |
Cambridge |
MA |
US |
|
|
Assignee: |
Sand 9, Inc.
Cambridge
MA
|
Family ID: |
49913500 |
Appl. No.: |
14/633885 |
Filed: |
February 27, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13941906 |
Jul 15, 2013 |
9000848 |
|
|
14633885 |
|
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61671962 |
Jul 16, 2012 |
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Current U.S.
Class: |
331/35 |
Current CPC
Class: |
H03B 21/02 20130101;
H03B 5/30 20130101; H03B 5/32 20130101; H03B 21/01 20130101; H03L
1/00 20130101; H03B 1/04 20130101; H03B 25/00 20130101 |
International
Class: |
H03B 1/04 20060101
H03B001/04; H03B 5/32 20060101 H03B005/32; H03L 1/00 20060101
H03L001/00 |
Claims
1. A method, comprising: generating a multiple-frequency output
signal of a piezoelectric mechanical resonating structure;
generating, from the multiple-frequency output signal, a correction
signal comprising at least one frequency; and combining the
correction signal and at least a portion of the multiple-frequency
output signal.
2. The method of claim 1, wherein generating the multiple-frequency
output signal comprises generating a first frequency comb, and
wherein generating the correction signal comprises generating a
second frequency comb.
3. The method of claim 2, wherein the mechanical resonating
structure is configured to exhibit multiple resonance modes, and
wherein generating the first frequency comb comprises exciting the
multiple resonance modes of the mechanical resonating
structure.
4. The method of claim 2, wherein generating the first frequency
comb comprises nonlinearly exciting the mechanical resonating
structure.
5. The method of claim 2, wherein generating the second frequency
comb comprises mixing the multiple-frequency output signal.
6. The method of claim 1, wherein combining the correction signal
and at least a portion of the multiple-frequency output signal
comprises performing a subtraction operation.
7. The method of claim 1, wherein generating the correction signal
comprises processing first and second frequencies of the
multiple-frequency output signal.
8. The method of claim 1, wherein combining the correction signal
and at least the portion of the multiple-frequency output signal
produces a combined signal comprising a target frequency, and
wherein the combined signal comprising the target frequency has
greater stability than the multiple-frequency output signal.
9. The method of claim 1, wherein combining the correction signal
and at least the portion of the multiple-frequency output signal
produces a combined signal comprising a target frequency, and
wherein the combined signal comprising the target frequency has
improved noise characteristics compared to the multiple-frequency
output signal.
10. A timing oscillator, comprising: a piezoelectric mechanical
resonator; a driving circuit configured to excite the mechanical
resonator, wherein the mechanical resonator is configured to
produce a multiple-frequency output signal in response to being
excited by the driving circuit; correction circuitry configured to
generate, from the multiple-frequency output signal, a correction
signal comprising at least one frequency; and combination circuitry
configured to combine the correction signal and at least a portion
of the multiple-frequency output signal.
11. The timing oscillator of claim 10, wherein the
multiple-frequency output signal comprises a first frequency comb,
and wherein the correction signal comprises a second frequency
comb.
12. The timing oscillator of claim 11, wherein the mechanical
resonator is configured to exhibit multiple resonance modes, and
wherein the driving circuit is configured to excite the multiple
resonance modes of the mechanical resonator.
13. The timing oscillator of claim 12, wherein the multiple
resonance modes include a target resonance mode and at least one
spurious resonance mode, and wherein the at least one spurious
resonance mode is associated with a coupling between a suspended
portion of the mechanical resonator and at least one anchor.
14. The timing oscillator of claim 11, wherein the driving circuit
is configured to nonlinearly excite the mechanical resonator.
15. The timing oscillator of claim 11, wherein the timing
oscillator comprises mixing circuitry, wherein the mixing circuitry
includes the correction circuitry and the combination circuitry,
and wherein the mixing circuitry is configured to generate the
second frequency comb at least in part by mixing the
multiple-frequency output signal.
16. The timing oscillator of claim 10, wherein the correction
circuitry is configured to generate the correction signal by
processing at least two separate frequencies of the
multiple-frequency output signal.
17. The timing oscillator of claim 10, wherein the combination
circuitry comprises circuitry configured to perform a subtraction
operation to produce a combined signal.
18. The timing oscillator of claim 17, wherein the combined signal
comprises a target frequency, and wherein the combined signal
comprising the target frequency has greater stability than the
multiple-frequency output signal.
19. The timing oscillator of claim 17, wherein the combined signal
comprises a target frequency, and wherein the combined signal
comprising the target frequency has improved noise characteristics
compared to the multiple-frequency output signal.
20. The timing oscillator of claim 10, wherein the mechanical
resonator comprises silicon.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit under 35 U.S.C.
.sctn.120 as a continuation of U.S. application Ser. No.
13/941,906, entitled "NOISE REDUCTION IN MEMS OSCILLATORS AND
RELATED APPARATUS AND METHODS," filed on Jul. 15, 2013 under
Attorney Docket No. G0766.70051US01, which is incorporated herein
by reference in its entirety.
[0002] U.S. application Ser. No. 13/941,906 claims the benefit
under 35 U.S.C. .sctn.119(e) of U.S. Provisional Application Ser.
No. 61/671,962, entitled "NOISE REDUCTION IN MEMS OSCILLATORS AND
RELATED APPARATUS AND METHODS" filed on Jul. 16, 2012 under
Attorney Docket No. G0766.70051US00, which is hereby incorporated
herein by reference in its entirety.
BACKGROUND
[0003] 1. Field
[0004] The present application relates to noise reduction in
oscillators, such as MEMS oscillators, and related apparatus and
methods.
[0005] 2. Related Art
[0006] Mechanical resonating structures, such as
micro-electro-mechanical systems (MEMS) resonators, generate
oscillating signals when excited by an appropriate drive signal.
The oscillating signals are typically characterized by one or more
target frequencies in addition to other frequencies constituting
noise.
SUMMARY
[0007] According to an aspect of the present application, a method
is provided, comprising generating a multiple-frequency output
signal of a mechanical resonating structure, generating, from the
multiple-frequency output signal, a correction signal comprising at
least one frequency, and combining the correction signal and at
least a portion of the multiple-frequency output signal.
[0008] According to an aspect of the present application, a timing
oscillator is provided, comprising a mechanical resonator and a
driving circuit configured to excite the mechanical resonator. The
mechanical resonator is configured to produce a multiple-frequency
output signal in response to being excited by the driving circuit.
The timing oscillator further comprises correction circuitry
configured to generate, from the multiple-frequency output signal,
a correction signal comprising at least one frequency. The timing
oscillator further comprises combination circuitry configured to
combine the correction signal and at least a portion of the
multiple-frequency output signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Various aspects and embodiments of the technology will be
described with reference to the following figures. It should be
appreciated that the figures are not necessarily drawn to scale.
Items appearing in multiple figures are indicated by the same or
similar reference number in all the figures in which they
appear.
[0010] FIG. 1A illustrates the amplitude of the electric field of a
continuous wave monochromatic laser as a function of time.
[0011] FIG. 1B illustrates the electric field of the continuous
wave monochromatic laser of FIG. 1A in the frequency domain, with
the y-axis representing intensity and the x-axis representing
frequency.
[0012] FIG. 2 illustrates a frequency comb, with the y-axis
representing intensity and the x-axis representing frequency.
[0013] FIG. 3 illustrates a timing oscillator, according to a
non-limiting embodiment.
DETAILED DESCRIPTION
[0014] The inventors have appreciated that the electrical noise of
signals produced by a mechanical resonator may be reduced or
eliminated using frequency comb techniques. A mechanical resonator
output signal exhibiting multiple frequencies establishing a
frequency comb may be suitably processed to generate therefrom a
second frequency comb. Suitable combination of the first and second
frequency combs may produce a signal of a target frequency having
less noise than that of the initial output signal of the mechanical
resonator.
[0015] According to an aspect, a timing oscillator including a
mechanical resonator and configured to produce an output signal of
a target frequency (e.g., a frequency matching or consistent with
design specifications) having low noise is described. The timing
oscillator may include drive circuitry configured to excite the
mechanical resonator. Suitable excitation may result in the
mechanical resonator producing an output signal having multiple
frequencies. The output signal may be processed by suitable
circuitry to generate a correction signal. Combination circuitry
may suitably combine the output signal of the mechanical resonator
and the correction signal to produce the output signal of the
timing oscillator having the target frequency.
[0016] The aspects described above, as well as additional aspects,
are described further below. These aspects may be used
individually, all together, or in any combination of two or more,
as the technology is not limited in this respect.
[0017] Frequency comb spectroscopy is an optical technique using
ultrafast lasers for high precision measurement of frequencies for
metrology applications. Such operation is described in connection
with FIGS. 1A, 1B and 2.
[0018] A monochromatic continuous wave (CW) laser has a single
wavelength, as shown in FIG. 1A, which illustrates the magnitude of
the electric field of a wave 102 as a function of time. In the
frequency domain, a monochromatic CW laser is represented by a
single frequency. If the monochromatic CW laser is ideal, it is
represented in the frequency domain by a delta function 104, as
shown in FIG. 1B, in which the y-axis represent intensity and the
x-axis represents frequency.
[0019] A frequency comb contains a number of single-frequency
fields spanning over a frequency range, with each individual
frequency field representing a tooth in the comb, as shown in FIG.
2, which illustrates a frequency comb 200 containing seven discrete
frequencies 202a-202g.
[0020] Optical frequency combs (i.e., frequency combs generated
with an optical source, such as a laser) are used to measure
frequencies because of their ability to measure high frequencies
with high accuracy. The physical distance between the teeth of the
optical frequency comb can be determined and corresponds to the
difference in frequency between the teeth. When the frequency of a
target signal of unknown frequency is to be measured, the target
signal may be represented in the frequency domain and superimposed
on the optical frequency comb. The relative position of the target
signal in the frequency domain compared to the teeth of the optical
frequency comb is used to determine the frequency of the target
signal. For instance, if the target signal is located midway
between two teeth of the frequency comb in the frequency domain,
then the frequency of the target signal is in the middle of the
respective frequencies of the teeth between which the target signal
lies.
[0021] The individual frequencies of an optical frequency comb may
be in the terahertz (THz) range, thus allowing for frequency
measurements in that range, which conventional frequency
measurement circuitry may not be capable of measuring. The
difference between frequencies of an optical frequency comb (i.e.,
the frequency difference between distinct teeth of the optical
frequency comb) may be in the gigahertz (GHz) range. Thus,
frequency measurements of target signals having high frequencies
(in the terahertz range) can be made with high accuracy (in the
gigahertz range).
[0022] The inventors have appreciated that, in the context of
mechanical resonators and the signals produced therefrom, frequency
combs may be used for a different purpose than to measure signal
frequencies. That is, frequency combs may be used in the context of
mechanical resonators to generate electrical signals of a target
frequency with low noise.
[0023] Accordingly, non-limiting aspects of the present application
provide methods and apparatus utilizing frequency comb techniques
to generate electrical signals having a target frequency with
reduced or eliminated noise. The apparatus may include a mechanical
resonator (e.g., a micro-electro-mechanical systems (MEMS)
resonator) and suitable circuitry for driving the mechanical
resonator as well as processing signals output by the mechanical
resonator.
[0024] According to an aspect of the present application, a
MEMS-resonator based timing oscillator is provided that generates a
frequency comb of multiple frequency signals. The relationship
between these frequencies (or teeth) may be used to generate a
single final frequency, which is superior in terms of stability and
noise characteristics compared to a conventional MEMS-resonator
based timing oscillator.
Comb Generation
[0025] As mentioned, various aspects of the present application
involve generation of a frequency comb from a mechanical resonator.
Non-limiting examples of manners in which such a frequency comb may
be generated are now described.
[0026] A micro-electro-mechanical systems (MEMS) resonator is a
passive component (in that the resonator's oscillation is excited
by a driving force from an external source) which may be operated
in a single mode of resonance, corresponding to a single frequency.
By the use of an electronic circuit on a board or integrated
circuit, self-sustained oscillation can be created with the MEMS
resonator, and thus a timing oscillator may be formed. Typically,
the electronic circuit coupled to the MEMS resonator is configured
to reduce additional signals around the central frequency of
interest that may be generated by unwanted resonances in the
resonator or in the circuit elements. These so-called spurious
signals are conventionally considered detrimental to the operation
of the timing oscillator as a single frequency source.
[0027] However, MEMS resonators usually have many resonance modes.
In non-ideal timing oscillator systems, the driving circuit can
excite more than one mode. Multiple modes can also be excited
because of non-ideal designs of the resonator, where the resonance
mode of interest can be intrinsically coupled to other modes. One
typical example of this is the coupling between the suspended part
of the MEMS resonator and the anchors, which results in spurious
modes. In the frequency domain, these spurious modes appear as
sidebands of the main resonant mode, as given by Equation 1:
f.sub.n=f.sub.0+[sgn(f.sub.s-f.sub.0)]f.sub.s [Eq. 1]
[0028] Here, the sign function sgn(x) determines whether the
spurious mode is to the left or to the right of the central
frequency f.sub.0. The index s spans over the number of spurious
mode frequencies, and n represents an integer.
[0029] Thus, a frequency comb may be generated as an output signal
of a mechanical resonator by exciting multiple modes of the
mechanical resonator.
[0030] Another manner in which a multiple frequency output (e.g., a
frequency comb) of a MEMS-based timing oscillator may be generated
is via nonlinear driving. If the driving circuit is used to drive
the MEMS resonator nonlinearly at a specific resonance mode, then
the oscillator output may display harmonics of the primary
oscillation. The output signal contains a series of frequencies,
which, in the frequency domain, resemble a comb. This may be an
ideal comb as the separation between the teeth of the comb may be
constant, as given by Equation 2:
f.sub.n=nf.sub.0 [Eq. 2]
where n is an integer and f.sub.0 is the central frequency.
Noise Cancellation Using a Frequency Comb
[0031] Once a frequency comb is established, then the frequency
comb may be used for noise cancellation. Noise cancellation may be
achieved by performing mathematical operations to obtain an output
at the target frequency by subtraction or cancellation of the noise
components.
[0032] Consider an ideal frequency comb, represented in the
frequency domain by Equation 3:
f.sub.n=f.sub.0+nf.sub.r, [Eq. 3]
where n is an integer and f.sub.r is the comb tooth spacing. If the
comb spans an octave in frequency (a factor of 2), then it is known
as an octave-spanning comb. As an example, Equation 4 shows how
background noise can be cancelled, and a signal with improved noise
characteristics compared to that of the initially produced comb may
be produced.
2f.sub.n-f.sub.2n=(2f.sub.0+2nf.sub.r)-(f.sub.0+2nf.sub.r)=f.sub.0
[Eq. 4]
[0033] Any suitable circuitry may be used to perform the
functionality of Equation 4. For example, a timing oscillator
including a mechanical resonator may further include processing
circuitry (e.g., correction and/or combination circuitry) for
performing the operations illustrated in Equation 4. A non-limiting
example of such processing circuitry is shown in FIG. 3.
[0034] As shown, the timing oscillator 300 comprises a resonator
302 (e.g., a MEMS resonator or any other suitable resonator), a
driving circuit 304 coupled to the resonator 302 in a feedback loop
and configured to excite the resonator 302, correction circuitry
306, and combination circuitry 308. The correction circuitry 306
may receive the output signal 310 of the resonator 302 and generate
a correction signal 312 by any suitable processing. The combination
circuitry 308 is configured to receive both the output signal 310
of the resonator 302 and the correction signal 312 from the
correction circuitry 306 and generate an output signal 314 of the
timing oscillator 300.
[0035] According to a non-limiting embodiment, the output signal
310 of the resonator 302 is a first frequency comb, the correction
circuitry 306 generates a second frequency comb as the correction
signal 312, and the combination circuitry 308 combines the first
and second frequency combs suitably to produce an output signal 314
having a single frequency with lower noise (and higher stability in
some cases) than either the first or second frequency combs.
Alternatives are possible, however.
[0036] According to an aspect of the present application, frequency
comb techniques may be applied in the context of mechanical
resonators for functions other than (or in addition to) noise
reduction. For example, frequency comb techniques may be applied
for signal down conversion or up conversion, timing synchronization
in a network, frequency multiplication and parametric
amplification.
[0037] One or more aspects of the present application may provide
various benefits. Some non-limiting examples are now described.
However, it should be appreciated that not all aspects necessarily
provide all listed benefits, and that additional benefits other
than those listed may be provided. One or more aspects may provide
timing oscillators producing a target output reference frequency
with superior phase noise characteristics compared to conventional
timing oscillators. Jitter may also (or alternatively) be reduced
or eliminated. In addition, the reference frequency can also
provide a higher degree of stability.
[0038] Mechanical resonating structures as described herein may be
varied in multiple ways. These include choice of material--silicon
is still the material of choice for most integrated circuits, but
other materials might be more commercially expedient. Piezoelectric
materials such as Aluminum Nitride (AlN) have shown much promise
because of its intrinsically high stiffness (yielding high
frequencies), low-temperature deposition methods, and ease of
actuation/detection. Other materials include (but are not limited
to) metals, other piezoelectric materials (quartz, ZnO), CVD
diamond, semiconductors (GaAs, SiGe, Si), superconducting
materials, and heterostructures of all kinds
(piezoelectric/semiconductor, semiconductor/metal, bimetal, etc.).
The resonator can be operated in a variety of ways, including
piezoelectric, magnetomotive, magnetostatic, electrostatic
capacitive transduction, optical, thermoelastic, thermomechanical,
and piezoresistive. These methods can be used both in actuation and
detection. A hybrid combination of these methods is also a
possibility.
[0039] Mechanical resonating structures as described herein may be
implemented in various devices. For example, timing oscillators,
temperature compensated MEMS oscillators, oven-controlled MEMS
oscillators, cellular phones, personal digital assistants (PDAs),
personal computers, RFID tracking devices, GPS receivers,
wireless-enabled appliances and peripherals (printers, digital
cameras, household appliances), satellite radio receivers
(Sirius/XM), military platforms, metrology devices, automobiles,
land vehicles, airplanes, drones, blimps, zeppelins, ships and
boats, kayaks, range finders, personal navigation devices (PNDs),
laptops, tablet computers, femtocells, implantable location
trackers and any location aware device are all examples of devices
which may utilize one or more aspects of the present application.
The mechanical resonating structures in such devices may operate in
various capacities, for example as passive or active components, as
filters, duplexers, switches and timing oscillators. Inertial
navigation systems also use MEMS resonators in gyroscopes,
accelerometers, magnetometers and altimeters, all of which contain
a resonating structure. Apart from wireless and navigation-based
applications, MEMS-based resonators are also used in optical
switches, routers and display systems.
[0040] The mechanical resonating structures described herein may be
used as stand-alone components, or may be incorporated into various
types of larger devices. Thus, the various structures and methods
described herein are not limited to being used in any particular
environment or device. However, examples of devices which may
incorporate one or more of the structures and/or methods described
herein include, but are not limited to, tunable meters, mass
sensors, gyroscopes, accelerometers, switches, and electromagnetic
fuel sensors. According to some embodiments, the mechanical
resonating structures described are integrated in a timing
oscillator. Timing oscillators are used in devices including
digital clocks, radios, computers, oscilloscopes, signal
generators, and cell phones, for example to provide precise clock
signals to facilitate synchronization of other processes, such as
receiving, processing, and/or transmitting signals. In some
embodiments, one or more of the devices described herein may form
part or all of a MEMS.
[0041] While various aspects have been described as implementing
frequency combs, it should be appreciated that not all aspects are
limited in this respect. For example, aspects of the present
application may apply to any multiple-frequency output signal of a
mechanical resonator, whether that multiple-frequency output signal
constitutes a frequency comb or not. Similarly, correction signals
of the types described herein may include one or more frequencies,
as a frequency comb is a non-limiting example of a suitable
correction signal. Further alternatives are possible.
[0042] It should be understood that the various embodiments shown
in the Figures are illustrative representations, and are not
necessarily drawn to scale. Reference throughout the specification
to "one embodiment" or "an embodiment" or "some embodiments" means
that a particular feature, structure, material, or characteristic
described in connection with the embodiment(s) is included in at
least one embodiment, but not necessarily in all embodiments.
Consequently, appearances of the phrases "in one embodiment," "in
an embodiment," or "in some embodiments" in various places
throughout the Specification are not necessarily referring to the
same embodiment.
[0043] Unless the context clearly requires otherwise, throughout
the disclosure, the words "comprise," "comprising," and the like
are to be construed in an inclusive sense as opposed to an
exclusive or exhaustive sense; that is to say, in a sense of
"including, but not limited to." Additionally, the words "herein,"
"hereunder," "above," "below," and words of similar import refer to
this application as a whole and not to any particular portions of
this application. When the word "or" is used in reference to a list
of two or more items, that word covers all of the following
interpretations of the word: any of the items in the list; all of
the items in the list; and any combination of the items in the
list.
[0044] Having thus described several aspects of at least one
embodiment of the technology, it is to be appreciated that various
alterations, modifications, and improvements will readily occur to
those skilled in the art. Such alterations, modifications, and
improvements are intended to be within the spirit and scope of the
technology. Accordingly, the foregoing description and drawings
provide non-limiting examples only.
* * * * *