Embodiments of voltage-controlled oscillators for wireless transmission of data are disclosed herein. In one example, an oscillator circuit includes an active network, a passive differential network coupled to the active network, and a tail tank connected to the active network through a low impedance point of the active network is disclosed. The active network is configured to generate an activating signal for sustaining oscillation of the oscillator circuit. The passive differential network has a first input impedance magnitude peak at a first frequency and a second input impedance magnitude peak at a second frequency. The tail tank circuit has a third input impedance magnitude peak at a third frequency.

A sensing sensor includes an oscillator circuit, a base, a connection portion, and a temperature changing unit. The oscillator circuit oscillates the piezoelectric resonator. The base includes a base main body in which a depressed portion is provided and a lid portion at one side, supports the piezoelectric resonator at another side, and is for taking the oscillation frequency to an outside of the sensing sensor. The depressed portion houses the oscillator circuit. The lid portion covers the depressed portion. The connection portion is disposed at the one side of the base and connected to a cooling mechanism for cooling the base from the one side. The temperature changing unit is interposed between the piezoelectric resonator and the base, so as to cool and heat the piezoelectric resonator and transfer a heat radiated for cooling the piezoelectric resonator from the other side of the base to the one side.

Certain aspects of the present disclosure provide methods and apparatus for reducing phase noise in voltage-controlled oscillators (VCOs). One example VCO generally includes a first resonant circuit comprising an inductor and a first variable capacitive element coupled in parallel with the inductor; and a second variable capacitive element coupled to a center tap of the inductor and further coupled to a reference voltage, wherein the center tap of the inductor is further coupled to a voltage source.

A high-power transmitter with a fully-integrated phase Iocking capability is disclosed and characterized. Also provided herein is a THz radiator structure based on a return-path gap coupler, which enables the high-power generation of the disclosed transmitter, and a self-feeding oscillator suitable for use with the transmitter.

A substance detection system and a substance detection method are provided. The temperature identifying portion identifies a surface temperature of the quartz substrate, based on a difference between a deviation of the fundamental wave frequency from at least any predetermined reference fundamental wave frequency of the reference crystal resonator and the detecting crystal resonator and a deviation of the third harmonic frequency from a predetermined reference third harmonic frequency. The substance identifying portion identifies a temperature at which a contaminant attached to the detecting crystal resonator is desorbed from the detecting crystal resonator to identify the contaminant based on the temperature at which the contaminant is desorbed. The temperature is identified based on a difference between the fundamental wave frequency of the reference crystal resonator and the fundamental wave frequency of the detecting crystal resonator measured by the frequency measuring portion and the temperature identified by the temperature identifying portion.

A digital modulating device includes an oscillator that generates an oscillation signal, and a frequency doubling modulator that includes: a single-ended to differential converter converting the oscillation signal into two periodic signals; two inductors respectively receiving the periodic signals and respectively providing two input signals; a switching circuit; and two amplifier circuits. When the switching circuit operates in a first state, the amplifier circuits respectively amplify the input signals to respectively generate two amplified signals that are combined into a combined signal at a common node thereof. When the switching circuit operates in a second state, the amplifier circuits do not perform amplification.

A digital modulating device includes an oscillator that generates an oscillation signal, and a frequency doubling modulator that includes: a single-ended to differential converter converting the oscillation signal into two periodic signals; two inductors respectively receiving the periodic signals and respectively providing two input signals; a switching circuit; and two amplifier circuits. When the switching circuit operates in a first state, the amplifier circuits respectively amplify the input signals to respectively generate two amplified signals that are combined into a combined signal at a common node thereof. When the switching circuit operates in a second state, the amplifier circuits do not perform amplification.

A system includes a signal generator and a signal combiner. The signal generator is configured to output a first signal having a first frequency and to output one or more signals having the first frequency and having phases shifted relative to the first signal by predetermined amounts. The signal combiner is configured to combine the first signal and the one or more signals to output a frequency multiplied second signal having a second frequency. The second frequency is greater than the first frequency.

Certain aspects of the present disclosure provide methods and apparatus for reducing phase noise in voltage-controlled oscillators (VCOs). One example VCO generally includes a first resonant circuit comprising an inductor and a first variable capacitive element coupled in parallel with the inductor; and a second variable capacitive element coupled to a center tap of the inductor and further coupled to a reference voltage, wherein the center tap of the inductor is further coupled to a voltage source.

A high-power transmitter with a fully-integrated phase Iocking capability is disclosed and characterized. Also provided herein is a THz radiator structure based on a return-path gap coupler, which enables the high-power generation of the disclosed transmitter, and a self-feeding oscillator suitable for TS use with the transmitter.