A local oscillator frequency-based proximity sensor is disclosed. The proximity sensor includes: an integrated circuit having at least a capacitive element; and an antenna designed with an inductive element; wherein the capacitive element and the inductive element form a proximity sensor oscillating at a local oscillator (LO) frequency, wherein the integrated circuit is configured to measure a frequency offset from the LO frequency, wherein the frequency offset is indicative of a detection of a nearby object.

An apparatus includes a microelectromechanical system (MEMS) die having a first surface and an opposing second surface. The MEMS die includes a surface-mounted resonator on the first surface and includes a first inductor. The apparatus also includes first and second dies. The first die has a third surface and an opposing fourth surface. The first die is coupled to the MEMS die such that the third surface of the first die faces the first surface of the MEMS die. The first and second surfaces are spaced apart. The first die includes an oscillator circuit and a second inductor. The oscillator circuit is coupled to the second inductor. The second inductor is inductively coupled to the first inductor. The second die is electrically coupled to the first die.

Provided is a constant voltage output circuit having an output terminal and configured to supply power to a crystal oscillator circuit connected to the output terminal, the constant voltage output circuit, having: a bias current control circuit subjected to negative feedback control by an output voltage which is supplied from the output terminal. As a result, variation in the constant voltage output caused by variation in current from a constant current source is reduced.

A crystal oscillator includes a crystal resonator; an inverting amplifier configured to be coupled between a pair of excitation electrodes of the crystal resonator; and a control circuit configured to initiate an alarm and raise gain of the inverting amplifier in a case where an index value for representing oscillation amplitude of the crystal resonator in an oscillation state is equal to or lower than a reference value.

Provided is a constant voltage output circuit having an output terminal and configured to supply power to a crystal oscillator circuit connected to the output terminal, the constant voltage output circuit, having: a bias current control circuit subjected to negative feedback control by an output voltage which is supplied from the output terminal. As a result, variation in the constant voltage output caused by variation in current from a constant current source is reduced.