Piezoelectric acoustic metamaterial resonators include a piezoelectric substrate having a top surface and a bottom surface and a plurality of magnetostrictive members disposed on the top surface of the piezoelectric substrate and extending along a length of the piezoelectric substrate and spaced across a width of the piezoelectric substrate.

A circuit device includes an oscillation circuit. The oscillation circuit includes a first variable capacitance circuit whose capacitance change characteristic with respect to a capacitance control voltage is a positive characteristic and a second variable capacitance circuit whose capacitance change characteristic with respect to the capacitance control voltage is a negative characteristic, and oscillates a resonator. The circuit device further includes a switch circuit. The switch circuit receives a first input voltage at a first input terminal thereof, receives a second input voltage at a second input terminal thereof, outputs a first output voltage selected from a plurality of voltages including the first input voltage and the second input voltage to a first output terminal thereof to which the first variable capacitance circuit is electrically coupled, and outputs a second output voltage selected from the plurality of voltages to a second output terminal thereof to which the second variable capacitance circuit is electrically coupled.

In one embodiment, a piezo-resistive resonator device includes one or more drive transistors with source and drain regions in a first well and a sense transistor with source and drain regions in a second well of opposite polarity than the first well. The gates of the drive and sense transistor are connected to a first direct current (DC) source. The drain region of the sense transistor is connected to a second DC source, and the source and drain regions of the drive transistor are connected to an alternating current (AC) source.

In one embodiment, a piezo-resistive resonator device includes one or more drive transistors with source and drain regions in a first well and a sense transistor with source and drain regions in a second well of opposite polarity than the first well. The gates of the drive and sense transistor are connected to a first direct current (DC) source. The drain region of the sense transistor is connected to a second DC source, and the source and drain regions of the drive transistor are connected to an alternating current (AC) source.

An oscillator includes: a resonator; an oscillation circuit configured to oscillate the resonator; a first temperature compensation circuit configured to perform a first temperature compensation processing of temperature-compensating for a frequency of a first clock signal generated by oscillation of the resonator by the oscillation circuit; and a second temperature compensation circuit configured to receive the first clock signal subjected to the first temperature compensation processing, and to output a second clock signal subjected to a second temperature compensation processing based on the first clock signal. The first temperature compensation circuit is configured to perform a first-order first temperature compensation processing as the first temperature compensation processing. The second temperature compensation circuit is configured to perform a high-order second temperature compensation processing as the second temperature compensation processing.

A circuit device includes: an output circuit including a waveform-shaping circuit of an oscillation signal and configured to output an output clock signal based on a clock signal subjected to waveform-shaping; a bias voltage output circuit configured to output a bias voltage of the oscillation signal input to the waveform-shaping circuit; a comparator configured to compare a DC voltage obtained by smoothing the clock signal subjected to the waveform-shaping with a reference voltage; a logic circuit configured to set an adjustment value of the bias voltage; and a storage circuit. In a test mode, the logic circuit changes the adjustment value to determine a set value of the adjustment value based on output of the comparator when the adjustment value is changed, and stores the determined set value in the storage circuit.

A circuit device includes: an output circuit including a waveform-shaping circuit of an oscillation signal and configured to output an output clock signal based on a clock signal subjected to waveform-shaping; a bias voltage output circuit configured to output a bias voltage of the oscillation signal input to the waveform-shaping circuit; a comparator configured to compare a DC voltage obtained by smoothing the clock signal subjected to the waveform-shaping with a reference voltage; a logic circuit configured to set an adjustment value of the bias voltage; and a storage circuit. In a test mode, the logic circuit changes the adjustment value to determine a set value of the adjustment value based on output of the comparator when the adjustment value is changed, and stores the determined set value in the storage circuit.

A circuit device includes a first terminal to be coupled to one end of a resonator, a second terminal to be coupled to another end of the resonator, an amplifying element configured to amplify a signal from the first terminal to output the signal amplified to the second terminal, a first resistor element disposed on a signal path between an input node and an output node of the amplifying element, a capacitance element disposed on a signal path between the first terminal and the input node, and a first switch element configured to switch electrical coupling between the input node and a ground.

An oscillation circuit including an amplifier, a feedback resistor and a first switch circuit is provided. The amplifier inverts and amplifies an oscillation signal received from an input terminal thereof to provide an output oscillation signal at an output terminal thereof. The feedback resistor is coupled between the input terminal and the output terminal, and coupled with the first switch circuit in parallel. The first switch circuit conducts the input terminal to the output terminal in one of the following situations: (1) an input voltage of the oscillation signal is higher than an output voltage of the output oscillation signal by at least a first threshold value; and (2) the output voltage is higher than the input voltage by at least a second threshold value. The first switch circuit has a first on-state resistance smaller than a resistance of the feedback resistor.

A vibrating element includes a piezoelectric substrate having an excitation section adapted to excite a thickness-shear vibration, and provided with a step section in each of side surfaces on both ends, and a peripheral section having a thickness smaller than a thickness of the excitation section, and the peripheral section has at least one projection section disposed on both principal surfaces in an area where a vibratory displacement when the excitation section excites a vibration is sufficiently attenuated.