245results about How to "Improve phase noise" patented technology

The present invention relates to a frequency synthesizer comprising a main unit and a side unit. The main unit comprises a main phase detector to obtain a main control signal, a main oscillator that generates a main synthesized frequency output signal representing the frequency synthesizer output signal based on said main control signal, and a mixer that mixes said main synthesized frequency output signal with a side synthesized frequency output signal to obtain said mixer output signal. The side unit generates said side synthesized frequency output signal and comprises a frequency signal generation unit that provides a linear frequency sweep signal or a fixed-frequency control signal at a fine frequency resolution from said fixed-frequency side reference signal, and a side oscillator that generates said side synthesized frequency output signal based on said frequency sweep signal or said fixed-frequency control signal.

An equalizer for serial data communications can be configured to compensate for the effects of deterministic jitter. The equalizer can be configured to compensate a received serial data stream for the effects of data-dependent jitter as well as duty cycle distortion jitter. The equalizer can be configured to determine the value of one or more previously received symbols and compare them to a recovered symbol. The equalizer can adjust a variable delay positioned in the serial data path to introduce a delay into the data path that is based in part on the received data stream. The equalizer can be configured to vary the delay when any of the one or more previously received symbols is different from the recovered symbol, and can be configured to maintain a constant delay if the one or more previously received symbols is the same as the recovered symbol.

A differential voltage controlled oscillator (VCO) employed in a frequency synthesizer used as a local oscillator of a wireless communication on-chip transmitter/receiver is provided. More particularly, a differential current negative feedback VCO equipped with a current-current negative feedback circuit that suppresses low- and high-frequency noise is provided.

A differential current negative feedback VCO includes a resonator determining oscillation frequency, and an oscillator generating negative resistance. In the oscillator of the differential current negative feedback VCO, transistors Q1 and Q2 form a cross-coupled pair, and negative resistance is generated by positive feedback of the cross-coupled pair. And, transistors Q1 and Q3 together with an emitter resistor and a capacitor form a current negative feedback part, and transistors Q2 and Q4 together with an emitter resistor and a capacitor form another current negative feedback part which is disposed opposite to a resonator. Thus, the VCO operates differentially.

In the oscillator of the differential current negative feedback VCO, emitter noise currents generated by base noise voltages of Q1 and Q2 induced by low- and high-frequency noise sources in the bases of Q1 and Q2 are sampled by emitter resistors, amplified through bases of Q3 and Q4, and thus return to the bases of the Q1 and Q2 and suppress the base noise voltages. Measurement of the phase noise of the differential current negative feedback VCO reveals a phase noise reduction of approximately 25 dB compared to a conventional differential VCO.

The invention relates to a broadband low-phase noise frequency synthesizer without a frequency divider based on harmonic mixing. The frequency synthesizer comprises a harmonic extraction module, a phase-locked loop, a direct frequency digital synthesizer and a reference source. The harmonic extraction module is used for extracting multiple-harmonic components of the reference source; appropriate components are elected and provided for an interpolation mixer; meanwhile, a reference clock of the direct frequency digital synthesizer is provided. The phase-locked loop is used for locking output signals and reference signals of a voltage-controlled oscillator. A feedback loop of the phase-locked loop comprises a frequency mixer which is used for guaranteeing broadband frequency outputting. By adopting the broadband low-phase noise frequency synthesizer without the frequency divider based on harmonic mixing, the broadband output frequency range of over one octave can be realized; the frequency divider is thoroughly omitted in the feedback loop, so that phase noise is reduced greatly; the frequency synthesizer supports wide bands and can be applied to a signal source, a frequency spectrograph and other high-performance measuring instruments, thereby having a wider application range.

An optical transmitter for generating a modulated optical signal for transmission over a fiber optic link to a remote receiver including a laser; a modulator for directly amplitude modulating the laser with an analog RF signal to produce an optical signal including an amplitude modulated information-containing component; and a phase modulator coupled to the output of the laser for canceling the noise signals generated in the laser.

A self-calibrating shared-component dual synthesizer includes, for example, two frequency synthesizers that are adapted to operate (respectively) in transmit (TX) and receive (RX) modes. Each synthesizer can be selectively arranged to vary and optimize the phase noise in accordance with the TX and RX requirements associated with each mode as well as independently optimized for flexible low area floorplan to achieve low power, spectral fidelity and reduced test time, low cost built in self-calibration. The two frequency synthesizers are also adapted to provide a built-in self-test signals used for intermodulation testing and calibration.

Provided are a differential voltage-controlled oscillator (VCO) and a quadrature VCO using center-tapped cross-coupling of a transformer. The differential VCO and the quadrature VCO can be driven by low power through a current reuse structure and have an excellent phase noise characteristic by center-tapped cross-coupling through a transformer. Further, variable capacitance units for frequency variation are divided into variable capacitance units for coarse tuning and variable capacitance units for fine tuning. Therefore, it is possible to obtain a wide tuning range while voltage oscillation gain is reduced. Further, the differential VCO and the quadrature VCO are configured in such a manner that the respective variable capacitance units operate linearly throughout the entire capacitance region due to control voltage distribution by resistors. Accordingly, it is possible to obtain a linear control voltage-oscillation frequency characteristic. The quadrature VCO according to the present invention can output four-phase quadrature signals while having an excellent phase noise characteristic, without substrate loss and current consumption caused by the switching transistors.

A method and apparatus for a fast and automatic setting of the phase locked loop (PLL) output frequency that significantly improves linearity, locking range as well as spectrum purity, jitter and phase noise performances is disclosed. In one embodiment, a PLL frequency synthesizer is disclosed having a reconfigurable voltage controlled oscillator VCO with three modes of operation: a Linear-High-gain, Zero-gain, and Low-gain mode. During a first tuning operation, the VCO work in a linear high gain mode, enabling a totally analogue self-calibration of the PLL over a wide frequency tuning range and with a fast settling time. During this operation the control voltage at the input of the VCO is varied by the PLL until the appropriate output frequency is found. A method for providing a linear variation of the frequency over all the voltage tuning range during this mode is disclosed. When the loop is locked, the VCO is automatically switched to the Zero-gain mode while keeping its frequency unchanged. Its sensitivity to the noise in the control path is then practically eliminated and its phase noise performances significantly improved. If the frequency error and phase noise are sufficiently small for the considered application the tuning is stopped. If the error and phase noise are not sufficiently small the VCO is switched again to Low-gain mode and fine-tuning adjustment of the output frequency is achieved.

An oscillator, comprising: a pair of transistors to which source terminals are interconnected and to which drain and gate terminals are coupled by a positive feedback loop comprising an oscillator tank, wherein the source terminals of the transistors are connected to a current source configured to control physical parameters of the oscillator.

The invention relates to a nuclear magnetic resonance imaging radio frequency receiver, the receiver being adapted to receive analogue signals from at least one radio frequency receiver coil unit (122; 204; 306), the radio frequency receiver comprising an analogue-digital converter (408) to convert the analogue magnetic resonance signal into a first digital signal, a resampling and demodulation unit (414) to convert the first digital signal into a second digital signal, a communication interface (400: 600; 602) adapted for transmitting the second digital signal via a communication link (202), and a first clock generator (406) for generating a sampling clock, the sampling clock being the direct clock source for the analogue-digital converter (408), the first clock generator (406) being adapted to generate the sampling clock using a digital timing reference, the digital timing reference being received digitally via the communication link (202) by the communication interface (400: 600; 602), wherein the receiver further comprises a second clock generator (410) for generating a system clock, the system clock being the direct clock source for the resampling and demodulation unit (414), the second clock generator (410) being adapted to generate the system clock using the sampling clock.

In one embodiment of the present invention, two crystal oscillator circuits are coupled in parallel to provide differing performance according to mode. Generally, a first circuit provides low phase noise and high accuracy while a second circuit provides greater phase noise within an acceptable tolerance while consuming significantly less power in a low power mode of operation. The second circuit includes an entirely separate amplifier for the low power operation that tolerates a relatively smaller input signal swing but that consumes even less power. The first circuit, which comprises selectable amplification elements, and the second circuit are coupled in parallel with selectable resistive elements and capacitive elements to provide varying amounts of amplification and filtering according to whether an operational mode is in a startup mode, a normal mode, or a low power mode of operation.

A PLL function may be implemented as a dual-loop structure having a first PLL circuit which generates an intermediate signal from the reference signal, and a second PLL circuit which generates an output signal from the intermediate signal. The intermediate signal frequency is preferably chosen at a value in which potential interference signals do not have much energy. The first loop preferably has low bandwidth to provide good input jitter attenuation, while second loop preferably has higher bandwidth to reduce phase noise of the output signal. The circuit preferably provides for a choice of several different intermediate frequencies to allow use where different intermediate frequencies may exist in each system. Moreover, in a system having two such dual-loop PLL circuits, each can be configured with a different intermediate frequency, so that interference from one to the other is reduced.

The invention provides a true random number generator and a realization method of the rue random number generator. The realization method comprises the steps: after a VDD/VSS is electrified, a power management unit starts working and provides voltage for all units of the true random number generator; a biasing circuit provides a biasing voltage signal for a second clock source; the biasing circuit in the second clock source provides a biasing voltage for a voltage-controlled oscillator; after being processed by a processing unit, a signal generated from a noise source is used as a voltage signal of an input signal of the voltage-controlled oscillator, and an output signal of the voltage-controlled oscillator is used as the output CLK2 of the second clock source; a signal generated from a circular oscillator is processed by a buffer to obtain a signal which is used as the output CLK1 of a first clock source; digital mixing on the received CLK1 and CLK2 is conducted by a sampler (3) to generate random data; and a post-processing unit processes the received random data of the sampler and outputs a random sequence. With the adoption of true random number generator and the realization method, the phase noise of the oscillation signals can be improved, and the random characteristic of the generated random data is greatly enhanced.

Provided is an oscillator using an MEMS resonator, which can reduce an influence of noise of a TIA and improve phase noise characteristics of an oscillator output. The oscillator includes an MEMS resonator, a TIA, a buffer amplifier, and a current/voltage converter that couples, by electromagnetic induction, with a wiring line via which an output of the MEMS resonator is fed to the TIA, so as to convert a current flowing in the wiring line to a voltage and output the voltage to the buffer amplifier. Thus, the oscillator output is extracted from the current/voltage converter. Further, the current/voltage converter is provided in the form of an oscillation output coil provided so as to surround the wiring line in a noncontact manner, in which oscillation output coil one end is connected to ground and the other end is connected to the buffer amplifier.

A single loop PLL frequency synthesizer for operation in the MHz to GHz range, suitable for integration in integrated circuits, operates at high comparison frequencies thus achieving superior phase noise performance, having wide loop bandwidths while able to tune in small frequency steps. It is based on the fact that the output frequency and the reference clock frequency always have a rational relationship, and so can always be represented as a ratio of two integer numbers. This ratio is expanded into various expressions of equivalent fraction expansions taking the form of a series of divided, added or subtracted terms, each being a rational number in itself. This ratio is realized in hardware through stages of frequency conversions using single sideband mixers (either the upper or lower sideband, and frequency dividers. This process of frequency translation thus generates the comparison frequency to which the PLL phase-locks the VCO.

The invention relates to a low-phase noise frequency source. The low-phase noise frequency source includes a low-phase noise reference source which sends low-phase noise 400MHz reference signals and low-phase noise 1000MHz reference signals to a DDS and control module and sends low-phase noise 400MHz excitation signals to a harmonic generation module, the DDS and control module which sends low-phase noise baseband signals to an output module and sends control signals to the output module and the harmonic generation module, the harmonic generation module which sends low-phase noise local vibration signals to the output module, and the output module which performs frequency mixing, filtering and frequency division on the baseband signals and the local vibration signals so as to obtain low-phase noise 5MHz-1000MHz signals which are adopted as output signals. The low-phase noise frequency source of the invention has the advantages of wide band, low stray degree, fine resolution and the like.

A voltage control oscillator (VCO) includes a VCO circuit and a back-gate coupling circuit, wherein the VCO circuit includes at least a first transistor, a second transistor and a resonant cavity formed by an inductor and a capacitor. The back-gate coupling circuit is formed by a plurality of capacitors and a plurality of resistors. In the embodiments of the present invention, the capacitors are coupled to the back-gate terminals of the first transistor and the second transistor, so as to reduce the power consumption and the phase noise of the VCO.

The invention discloses an injection locking millimeter wave frequency divider based on a self-oscillation optical frequency comb and a frequency division method of the injection locking millimeter wave frequency divider. The frequency divider comprises a photoelectric hybrid oscillator, an optical comb modulator is arranged in an optical link of the photoelectric hybrid oscillator, and a band-pass filter is arranged in an electric link of the photoelectric hybrid oscillator; a millimeter wave signal to be subjected to frequency division is injected into the photoelectric hybrid oscillator; wherein the central frequency of the millimeter wave signal is an integral multiple of the central frequency of the band-pass filter, the optical frequency comb sideband generated by the photoelectric hybrid oscillator and the modulation sideband of the signal to be converted output a fundamental frequency signal in a beat frequency mode, and the fundamental frequency signal is located within the locking bandwidth range of the photoelectric hybrid oscillator. When a super-harmonic signal is injected into the oscillation loop and locked, the frequency division function of the injected millimeterwave signal can be realized, and the frequency divider has the characteristics of wide band, low phase noise and large frequency division ratio.

The LC tank of a VCO includes a main varactor circuit and temperature compensation varactor circuit coupled in parallel with the main varactor circuit. The main varactor is used for fine tuning. The temperature compensation varactor circuit has a capacitance-voltage characteristic that differs from a capacitance-voltage characteristic of the main varactor circuit such that the effects of common mode noise across the two varactor circuits are minimized. The LC tank also has a plurality of switchable capacitor circuits provided for coarse tuning. To prevent breakdown of the main thin oxide switch in each of the switchable capacitor circuits, each switchable capacitor circuit has a capacitive voltage divider circuit that reduces the voltage across the main thin oxide switch when the main switch is off.