Abstract: A resonating element has a quartz crystal substrate having a vibrating portion and a thin-walled portion that is thinner than the vibrating portion, and a pair of excitation electrodes respectively disposed on opposite surfaces of the vibrating portion. Moreover, in the excitation electrode, each of a pair of sides arranged in a Z?-axis direction is convexly curved toward the center so that the excitation electrode has a constricted portion in which a length in the Z?-axis direction increases gradually from a central portion toward both ends in an X-axis direction.

Abstract: A piezoelectric module includes a piezoelectric package and a circuit component package. The piezoelectric module includes a thermoset resin with solder particles interposed between a whole circumference of the opening end surface of the second depressed portion including the plurality of connecting terminals of the circuit component package and the outer bottom surface of the first depressed portion of the piezoelectric package. The plurality of external terminals of the piezoelectric package and the plurality of connecting terminals of the circuit component package are electrically connected by metal bonding. The whole circumference of the opening end surface of the second depressed portion of the circuit component package and the outer bottom surface of the first depressed portion of the piezoelectric package are bonded by melting and hardening of the thermoset resin that constitutes the thermoset resin with solder particles.

Abstract: A crystal oscillator is configured by accommodating a crystal blank that functions as a crystal unit and an IC chip that includes at least an oscillator circuit using the crystal blank into a container in an integrated manner. In the IC chip, the oscillator circuit is connected to the crystal unit via a pair of crystal connecting terminals, an output from the oscillator circuit is supplied to a plurality of output buffers. In relation to the crystal connecting terminal having a phase opposite to that of an output from the on/off controllable output buffer, an output terminal of this output buffer is disposed farther than an output terminal of the output buffer that is not subjected to the on/off control.

Abstract: A vibrator element includes a base portion, a vibrating arm extending from the base portion, a first electrode provided on the vibrating arm, a second electrode provided above the first electrode, a piezoelectric body arranged between the first electrode and the second electrode, and an insulating film arranged between the first electrode and the piezoelectric body, in which the material of the first electrode contains TiN, the material of the insulating film contains SiO2, and the material of the piezoelectric body contains AlN.

Abstract: In a resonator element, when a width of each of arm portions of vibrating arms along an X-axis direction is set to W1, a width of each of two portions with a groove interposed therebetween, along the X-axis direction, in a principal surface of the vibrating arm is set to W3, and 2×W3/W1 is set to ?, the relation of 14.2%<?<100% is satisfied.

Abstract: A resonator element is provided. A base portion includes a first base portion, a second base portion, and a connecting portion. The base portion includes a width-decreasing portion that is provided at an end of the connecting portion on the first base portion side and that has a width along an X-axis direction which continuously decreases toward the second base portion. An outer edge of the width-decreasing portion and an outer edge of the connecting portion form a continuous line that does not include a corner portion, when seen in a plan view. When an angle between a tangent of a portion of the curved line on the first base portion side and a segment parallel to the X-axis direction is set to ?, a relation of 0°<?<90° is satisfied.

Abstract: A piezoelectric oscillator has an insulating base having a housing portion where internal terminal pads are formed, an integrated circuit (IC) element having rectangular pads bonded to the internal terminal (IT) pads, and a piezoelectric oscillation element (POE) connected to the base and IC element. The IT pads include two opposing first IT pads connected to the POE, two opposing second IT pads, one of which is for AC output, and two opposing third IT pads formed between the first IT pads and the second IT pads. Along a part of perimeter of the first IT pads, the third IT pads and wiring patterns which respectively extend the third IT pads are formed as conductive paths for blocking radiation noise. The first IT pads and the second IT pads are spaced apart with the conductive paths interposed therebetween.

Abstract: A resonator element includes a base section, at least one pair of vibrating arms protruding from the base section, a support arm protruding from the base section, and a first through hole provided to the support arm, and penetrating the support arm in a thickness direction, and is fixed to an object via an adhesive entering the first through hole.

Abstract: A resonating element includes a resonator element that includes a vibrating portion and an excitation electrode provided on both main surfaces of the vibrating portion, an intermediate substrate in which the resonator element is mounted so as to be spaced from the excitation electrode, and a spiral electrode pattern that is provided on at least one main surface of the intermediate substrate, in which the electrode pattern is electrically connected to the excitation electrode.

Abstract: An oscillator circuit comprising first and second resonator terminals for connecting to respective terminals of a resonator. The oscillator circuit also comprises a first inverting amplifier connected between the first and second resonator terminals in a first mode of operation; and a back to back pair of second inverting amplifiers connected between the first and second resonator terminals in a second mode of operation. There is also provided a controller configured to compare an operational parameter of the oscillator circuit to a switchover threshold, and switch the oscillator circuit from the first mode of operation to the second mode of operation when the operational parameter exceeds the switchover threshold.

Abstract: Systems and methods for amplitude loop control for oscillators. In some embodiments, an electronic circuit may include oscillator circuitry configured to produce a periodic signal, and control circuitry operably coupled to the oscillator circuitry, the control circuitry including switched capacitor circuitry configured to determine a difference between maximum and minimum peak voltage values of the periodic signal, the control circuit configured to control a voltage amplitude of the periodic signal based upon the difference. In other embodiments, a method may include receiving a clock signal from a clock generator, determining, using a switched capacitor circuit, a first peak voltage value of the clock signal, determining, using the switched capacitor circuit, a second peak voltage value of the clock signal, and controlling a bias current applied to the clock generator based upon a difference between the first and second peak voltage values.

Abstract: A calibrated crystal warm-up method that can include determining the number of clock cycles of a crystal clock reference signal from a crystal oscillator occur during a single clock cycle of a low-power oscillator. Further, the determination can occur when the crystal oscillator is warmed up. The method can also include comparing a number of clock cycles of the crystal clock reference signal with a previously determined number of clock cycles of the crystal clock reference signal to indicate whether the crystal oscillator is warmed up. Further, the method can include counting the number of clock cycles of a low-power clock reference signal have occurred up until the time it has been determined that the crystal oscillator has been warmed up.

Abstract: An oscillator system having: an UHF oscillator, such as a SAW oscillator, for producing a signal having a controllable frequency; a passive vibration, suppressor mechanically coupled to the UHF oscillator for suppressing vibrations above a predetermined bandwidth BW1 on the UHF oscillator; and an active vibration suppressor. The active vibration suppressor includes an accelerometer for sensing vibrations within a predetermined bandwidth BW2 on the UHF oscillator; and an HF or VHF oscillator, such as a crystal oscillator, producing a signal having a frequency controlled by the accelerometer. A control loop having a bandwidth changeable with sensed vibration level is fed the oscillator and the UHF oscillator for controlling the frequency of the signal produced by the SAW oscillator in accordance with a difference between the signal produced the HF or VHF oscillator and the signal produced by the UHF oscillator, the control loop having a bandwidth BW3; where BW1<BW3<BW2.

Abstract: A signal generating circuit for a real time clock device is disclosed, having an oscillating circuit, a voltage detecting circuit, and a control circuit. The oscillating circuit is used for generating oscillating signals. The voltage detecting circuit is used for detecting a voltage level coupled with the signal generating circuit. The control circuit is coupled with the oscillating circuit and the voltage detecting circuit. When the voltage level detected by the voltage detecting circuit locates in a predetermined range, the control circuit configures the oscillating circuit to generate the oscillating signals with a larger current at a first interval and to generate the oscillating signals with a smaller current at a second interval. The control circuit further generates a clock signal according to the oscillating signals at a third interval.

Abstract: The invention relates to a frequency generator assembly, including at least one oscillator and an electronic signal processing device, which is designed in such a way that the electronic signal processing device provides an electric clock signal (f) having a defined frequency as an output signal of the frequency generator assembly, wherein the defined frequency depends on the vibration frequency of the oscillator, wherein the oscillator includes at least one micromechanical seismic mass which is vibrationally excited by at least one driving device, whereupon the electronic signal processing device generates and provides the electric clock signal (f) according to the vibration frequency of the at least one seismic mass.

Abstract: A temperature-compensated crystal oscillator includes a crystal resonator; and an oscillator circuit for performing temperature compensation.

Abstract: A oscillator device includes: a first substrate that has a first surface, a second surface, and a through hole extending between the first surface and the second surface; a crystal oscillator that is disposed on the first surface of the first substrate, the crystal oscillator including an electrode; a second substrate that is disposed on the crystal oscillator; a through electrode that is disposed in the through hole, that has a diameter smaller than a diameter of the through hole, that is electrically coupled to the electrode, and that extends between the first surface and the second surface; and a filling member with which an area between an inner wall of the through hole and the through electrode is filled.

Abstract: This invention is directed to achieve the oscillator circuit with a shorter oscillation stabilizing period and a lower consumption of the electric current. The oscillator circuit 10 has the amplifier circuit (inverter circuit 11), and the clock signal CLK is outputted from the output terminal of the inverter circuit 11. The inverter circuit 11 is configured from the first inverter 12 and the second inverter 13. The inverter circuit 11 is connected to the control circuit 30 and the control signal Ctrl controls the driving capacity of the inverter circuit 11. For example, high level control signals Ctrl 1 (H) and Ctrl 2 (H) are supplied to the first and the second inverters 12, 13 for a certain period of time right after the oscillator circuit 10 starts its operation until the oscillation is stabilized, operating both inverters. Then, either the first inverter 12 or the second inverter 13 continues its operation and the other inverter stops the operation.

Abstract: A bonding type crystal controlled oscillator includes a crystal package and a circuit package bonded by two-tier bonding. An anisotropy conductive adhesive is interposed between back surface of the crystal package facing the circuit package and an upper surface of the circuit package facing the crystal package. The anisotropy conductive adhesive includes a thermosetting resin containing solder micro particles dispersed in the thermosetting resin. Assuming that a thickness of the output terminal formed at the crystal package is C ?m, a thickness of the external terminal formed at the circuit package is D ?m, and an average outside diameter of the solder micro particles dispersed in the anisotropy conductive adhesive is E ?m the dimensional relation is set to (C+D)>E.

Abstract: Resistor bias circuitry is included in components of an XTAL oscillator system to reduce 1/f noise. An XTAL oscillator includes a resistor bias circuit attached to the XTAL core. A common mode feedback OP amp connected to the XTAL core also includes a resistor bias circuit. An XTAL oscillator chain includes an XTAL core, common mode feedback OP amp, common mode logic buffer (CML BF), and differential to CMOS converter (D2C) each with resistor bias circuitry.

Abstract: An electronic component includes: a base material having a first conductive section; an oscillation piece having a second conductive section; a first member which is covered with a third conductive section making conductive contact with the first and second conductive sections and is provided between the base material and the oscillation piece; and a second member which is provided so as to be surrounded with the base material, the oscillation piece, and the first member and holds the base material and the oscillation piece.

Abstract: Methods and systems are provided to calibrate an oscillator circuit to reduce frequency pulling as a result of a change in power to a portion of the oscillator circuit. In an embodiment, an oscillator is coupled to a clock buffer circuit and a tuning capacitor configured to tune a frequency of the oscillator to a baseline frequency required for cellular communications. A change in power to the clock buffer circuit initiates a change in an amount of capacitance seen by the oscillator, which negatively impacts the tuning of the oscillator. A register stores a frequency offset caused by the change in power, and the tuning capacitor is adjusted, using the frequency offset, in response to the change in power, such that the total amount of capacitance seen by the oscillator is not changed when the change in power occurs.

Abstract: A crystal oscillator may be configured to limit crystal drive level in the crystal oscillator by clamping via a diode-resistor branch, voltage applied to a drain pad of the crystal oscillator. The crystal oscillator may incorporate Pierce crystal oscillator based implementation. The crystal oscillator may comprise an on-chip main branch, comprising at least one transistor element; an on-chip drain branch connecting the main branch to a drain pad; an on-chip gate branch connecting the main branch to a gate pad. The diode-resistor branch may be connected to the drain branch, and may comprise at least one diode and at least one resistor element. The at least one diode and the at least one resistor element may be connected in series in the diode-resistor branch. The clamped voltage may be applied from an off-chip drain node, through the drain pad.

Abstract: A vibration element includes a piezoelectric substrate including a vibrating section and a thick section having a thickness larger than that of the vibrating section. The thick section includes a first thick section provided along a first outer edge of the vibrating section, a second thick section provided along a second outer edge, and a third thick section provided along another first outer edge. An inclined outer edge section that intersects with each of an X axis and a Z? axis is provided in a tip section of the piezoelectric substrate.

Abstract: A resonator includes a resonator element including a base section, vibrating arms extending from the base section, and a support arm disposed between the vibrating arms, a package adapted to support the resonator element, and electrically-conductive adhesives adapted to fix the support arm to the package, the support arm includes a tip portion and a width-decreasing portion having a width smaller than the width of the tip portion, and the electrically-conductive adhesive has contact with at least a part of the width-decreasing portion in a planar view.

Abstract: A resonator element includes a piezoelectric substrate including a vibrating section and a thick section having a thickness larger than that of the vibrating section. The thick section includes a first thick section provided along a first outer edge of the vibrating section, a second thick section provided along a second outer edge, and a third thick section provided along a third outer edge. A first inclined outer edge section that is inclined with respect to both of an X axis direction and a Z? axis direction is provided in a corner section of the piezoelectric substrate where the second thick section and the third thick section are connected to each other.

Abstract: A vibration element includes a piezoelectric substrate including a vibrating section and a thick section having a thickness larger than that of the vibrating section. The thick section includes a first thick section provided along a first outer edge of the vibrating section, a second thick section provided along a second outer edge thereof, and a third thick section provided along a third outer edge thereof. When a maximum size of the second thick section in the vibration direction is Lmax and a minimum size thereof is Lmin, an average size expressed by (Lmax+Lmin)/2 is 100 ?m or smaller.

Abstract: An oscillator that can suppress a solder crack caused by a temperature change by a simple structure at low cost and improve heat cycle resistance performance is provided. The oscillator includes an epoxy resin board and an electronic component mounted on the board. Two-terminal electrode patterns are formed on the board, and connected to terminal electrodes of the electronic component by solder. A projection is formed on each of the electrode patterns at a part connected to a corresponding terminal electrode to create a space between the terminal electrode and the electrode pattern, and the solder forms a fillet in the space. This contributes to enhanced adhesion strength of the solder.

Abstract: A resonator includes a resonator element, which includes a quartz crystal substrate formed of crystal, and a package in which the resonator element is housed. The quartz crystal substrate includes a base portion and two vibrating arms that are aligned in the X-axis direction of the crystal and extend from the base portion in the +Y?-axis direction (or the ?Y?-axis direction) of the quartz crystal. The principal surface of the base portion on the ?Z?-axis side (+Z?-axis side when the vibrating arms extend in the ?Y?-axis direction) in the quartz crystal is fixed to the package.

Abstract: An oscillator assembly which, in one embodiment, is an ovenized crystal oscillator assembly including an enclosure defined by a base and a lid which is seated on the base. The components of the oscillator assembly are supported by the base and located under the lid. The base and the lid together define an interior oven and are both preferably made of an insulative thermoplastic material to maximize the heat retention and oven performance of the oscillator assembly. In one embodiment, the lid and the base incorporate a clip for securing the lid to the base.

Abstract: A crystal resonator comprises a first vibrating region provided on a crystal wafer, a second vibrating region provided on the crystal wafer, the second vibrating region having a different thickness and positive/negative orientation of the X-axis from those of the first vibrating region, and excitation electrodes which are provided respectively on the first vibrating region and the second vibrating region for causing the vibrating regions to vibrate independently. Frequencies that change by different amounts from each other relative to a temperature change can be retrieved from one vibrating region and the other vibrating region. Thus, based on an oscillating frequency of the vibrating region in which a clear frequency change occurs relative to the temperature, the oscillating frequency of the other vibrating region can be controlled. Thereby, increases in the complexity of the crystal oscillator can be suppressed.

Abstract: A piezoelectric oscillation circuit includes: a Colpitts oscillation circuit; a first circuit unit which includes a circuit having a variable-capacity capacitor for controlling an oscillation frequency; a second circuit unit which includes a circuit having a resistance; and a piezoelectric resonator which includes a first terminal connected to the first circuit unit and the second circuit unit, and a second terminal connected to the Colpitts oscillation circuit. The Colpitts oscillation circuit connects the second terminal to a fixed potential via a dividing resistance. The second circuit unit connects the first terminal to the fixed potential via the resistance.

Abstract: Oscillators are described that have a highly stable output frequency versus the variation of supply voltage and different operating conditions such as temperature. The concepts are broadly applicable to various types of oscillators. The highly stable output is achieved with the use of self biasing loops. The circuits associated with providing constant harmonic output current can be used with the concept of a phi-null oscillator to further stabilize the output frequency.

Abstract: A semiconductor device according to an exemplary aspect of the invention is capable of being selectively switched between an oscillation circuit and a signal input-output circuit, and includes first and second external connecting terminals that are connectable to an oscillation device; an inverting amplifier an input side of which is electrically connected to the first external connecting terminal through a coupling capacitor and an output side of which is electrically connected to the second external connecting terminal; a feedback resistor connected to the input side and the output side of the inverting amplifier; a bias stabilization circuit that stabilizes a bias applied to the coupling capacitor; a first signal input-output portion connected to the first external connecting terminal; and a second signal input-output portion connected to the second external connecting terminal.

Abstract: A large gain is used to start up the oscillation of the crystal quickly. Once the oscillation starts, the amplitude is detected. A control circuit determines based on the measured amplitude to disable a low resistance path in the controlled switch array to reduce the applied gain below the power dissipation specification of the crystal. Another technique introduces a mixed-signal controlled power supply multi-path resistive array which tailors the maximum current to the crystal. A successive approximation register converts the amplitude into several partitions and enables/disables one of several power routing paths to the inverter of the oscillator. This allows a better match between the crystal selected by the customer and the on-chip drive circuitry to power up the oscillator without stressing the crystal. The “l/f” noise of the oscillator circuit is minimized by operating transistors in the triode region instead of the linear region.

Abstract: A method for manufacturing a quartz crystal unit, comprising the steps of forming a quartz crystal tuning fork shape having a quartz crystal tuning fork base, and first and second quartz crystal tuning fork tines, a quartz crystal tuning fork resonator having the quartz crystal tuning fork shape, forming at least one groove in at least one of opposite main surfaces of each of the first and second quartz crystal tuning fork tines, determining each of a length of the at least one groove and an overall length of the quartz crystal tuning fork resonator so that a series resistance R1 of a fundamental mode of vibration of the quartz crystal tuning fork resonator is less than a series resistance R2 of a second overtone mode of vibration thereof, housing the quartz crystal tuning fork resonator in a case, connecting a lid to the case, and disposing a metal or a glass in a through-hole of the case.

Abstract: An oscillation circuit section is provided which can attain the reduction of a consumed power amount and the reduction of a manufacturing cost. In a semiconductor device, voltages are generated to drive the oscillation circuit section by using a plurality of MOS transistors which are connected in serial and each of which is in a diode connection. At this time, each voltage is generated based on a power supply voltage and a ratio of the threshold voltages of the plurality of MOS transistors. Therefore, it is possible to suppress the threshold voltage of each MOS transistor, to save an area of each MOS transistor, and to reduce the consumed power amount of the oscillation circuit section.

Abstract: A system for managing a reference clock signal includes an XO; a signal buffer coupled to the XO and configured to drive a reference clock signal generated by the XO; and a first IC coupled to the signal buffer. The first IC includes an XO input buffer configured to receive the reference clock signal, to switch between an enabled, operational state and a disabled state, and to have a first operational impedance while in the enabled state; an impedance equivalence circuit configured to be in an enabled, operational state when the XO input buffer is in its disabled state and vice versa and to have a second operational impedance while in the enabled state that is equivalent to the first operational impedance; and a control mechanism configured to switch the XO input buffer and the impedance equivalence circuit between the enabled state and the disabled state.

Abstract: A crystal resonator includes a plate-shaped crystal element, excitation electrodes, and a second crystal region. The plate-shaped crystal element is supported to a supporting portion. The crystal element is configured to vibrate at a thickness shear vibration. The excitation electrodes are disposed at both surfaces of a first crystal region of the crystal element. The second crystal region is positioned outside with respect to the excitation electrodes. The second crystal region is formed at a peripheral edge portion of the crystal element so as to occupy a region of equal to or more than 75% of a whole circumference of the crystal element. The second crystal region has a positive/negative direction of an X-axis of a crystal different from a positive/negative direction of an X-axis of a crystal of the first crystal region.

Abstract: A crystal resonator includes a crystal element and excitation electrodes. The crystal element includes an ? crystal region and a ? crystal region that have mutually different positive/negative directions along an X-axis. Each two or more of the ? crystal regions and the ? crystal regions are alternately formed along a direction perpendicular to the X-axis. The excitation electrodes are formed on both surfaces of the respective ? crystal region and ? crystal region other than crystal regions positioned at both end portions of a row of the ? crystal regions and the ? crystal regions.

Abstract: Systems and methods for amplitude loop control for oscillators. In some embodiments, an electronic circuit may include oscillator circuitry configured to produce a periodic signal, and control circuitry operably coupled to the oscillator circuitry, the control circuitry including switched capacitor circuitry configured to determine a difference between maximum and minimum peak voltage values of the periodic signal, the control circuit configured to control a voltage amplitude of the periodic signal based upon the difference. In other embodiments, a method may include receiving a clock signal from a clock generator, determining, using a switched capacitor circuit, a first peak voltage value of the clock signal, determining, using the switched capacitor circuit, a second peak voltage value of the clock signal, and controlling a bias current applied to the clock generator based upon a difference between the first and second peak voltage values.

Abstract: A piezoelectric resonating element includes a piezoelectric substrate having a rectangular vibrating portion and a thick-walled portion, excitation electrodes and, and lead electrodes. The thick-walled portion includes a fourth thick-walled portion, a third thick-walled portion, a first thick-walled portion, and a second thick-walled portion. The third thick-walled portion includes a third slope portion and a third thick-walled body, and at least one slit is formed in the third thick-walled portion.

Abstract: An oscillator having a plurality of operatively coupled ring oscillators arranged in hyper-matrix architecture. The operatively coupled ring oscillators are either identical or non-identical and are coupled through a common inverter or tail current transistors. Due to the arrangement of the ring oscillators in a hyper-matrix structure, the ring oscillators are synchronized and resist any variation in frequency or phase thereby maintaining a consistent phase noise performance.

Abstract: A piezoelectric vibrating piece includes a pair of vibrating arm portions, a base portion which is arranged between a pair of vibrating arm portions, and connecting portions which connect proximal end portions of a pair of vibrating arm portions and a proximal end portion of the base portion. Narrow width portions are provided at the base of the base portion.

Abstract: A piezoelectric vibrating piece includes a pair of vibrating arm portions which are arranged with a center axis interposed therebetween, a base portion which is arranged between a pair of vibrating arm portions and fixed to the outside, and a pair of connecting portions which connect proximal end portions of a pair of vibrating arm portions and a proximal end portion of the base portion. The distance between distal end portions of the vibrating arm portions and the center axis is smaller than the distance between the proximal end portions of the vibrating arm portions and the center axis.

Abstract: Methods for compensating the existing crystal oscillator frequencies in extended temperature ranges. Utilizing existing crystal oscillators on any system design which may have quartz crystals with associated circuitry to deliver frequency or timing reference signals and increasing the accuracy of such by additional circuitry.

Abstract: A constant voltage circuit which can realize a low consumption current, and a crystal oscillation circuit using the constant voltage circuit. The constant voltage circuit is provided with a temperature characteristic regulation element, in order to minimize a difference between a negative slope of a voltage response of a constant voltage to a temperature change and a negative slope of a voltage response of the smallest operation voltage that can oscillate in the crystal oscillation circuit to the temperature change, so that the consumption current of the crystal oscillation circuit is decreased. When the constant current generated by the constant voltage circuit is decreased, the consumption current of the constant voltage circuit is decreased, and the consumption current of the whole oscillation device is decreased.

Abstract: The present invention provides a TSV-based oscillator WLP structure and a method for fabricating the same. The method of the present invention comprises steps: providing a silicon base having an oscillator unit disposed thereon; forming on the silicon base at least one package ring surrounding the oscillator unit; and disposing a silicon cap on the package ring to envelop the oscillator unit. The present invention adopts a cap and a base, which are made of the same material, to effectively overcome the problem of thermal stress occurring in a conventional sandwich package structure. Further, the present invention elaborately designs the wiring on the lower surface of the base to reduce the package size and decrease consumption of noble metals.

Abstract: A quartz crystal resonator element includes: a base portion and a pair of vibrating arms which extend from a first end portion of the base portion along a Y-axis direction. The base portion includes a second end portion provided on the opposite side to a first end portion in the Y-axis direction. The base portion is provided with a protrusion in at least one of a third end portion and a fourth end portion which respectively connect both ends of the first end portion and both ends of the second end portion.

Abstract: Apparatus to provide a time reference are disclosed herein. An example apparatus disclosed herein includes a resonator. A first cap is coupled to a first side of the resonator to define a first cavity, and a second cap is coupled to a second side of the resonator to define a second cavity. The first cavity and the second cavity provide a first vacuum in which the resonator is to resonate. The resonator, the first cap and the second cap have substantially identical thermal expansion coefficients. The example apparatus also includes a vacuum chamber surrounding the resonator, the first cap and the second cap. The vacuum chamber is to provide a second vacuum in which the resonator, the first cap and the second cap are disposed. A frequency of resonance of the resonator in the first vacuum is to provide a time reference.