Showing papers on "Frequency drift published in 1998"

Frequency stability degradation of an oscillator slaved to a periodically interrogated atomic resonator

Abstract: Atomic frequency standards using trapped ions or cold atoms work intrinsically in a pulsed mode. Theoretically and experimentally, this mode of operation has been shown to lead to a degradation of the frequency stability due to the frequency noise of the interrogation oscillator. In this paper a physical analysis of this effect has been made by evaluating the response of a two-level atom to the interrogation oscillator phase noise in Ramsey and multi-Rabi interrogation schemes using a standard quantum mechanical approach. This response is then used to calculate the degradation of the frequency stability of a pulsed atomic frequency standard such as an atomic fountain or an ion trap standard. Comparison is made to an experimental evaluation of this effect in the LPTF Cs fountain frequency standard, showing excellent agreement.

Frequency jittering control for varying the switching frequency of a power supply

Abstract: EMI emission is reduced by jittering the switching frequency of a switched mode power supply. An oscillator with a control input for varying the oscillator's switching frequency generates a jittered clock signal. In one embodiment, the oscillator is connected to a counter clocked by the oscillator. The counter drives a digital to analog converter, whose output is connected to the control input of the oscillator for varying the oscillation frequency. In another embodiment, the oscillator is connected to a low frequency oscillator whose low frequency output is used to supplement the output of the oscillator for jittering the switching frequency. The invention thus deviates or jitters the switching frequency of the switched mode power supply oscillator within a narrow range to reduce EMI noise by spreading the energy over a wider frequency range than the bandwidth measured by the EMI test equipment.

Method and apparatus for measuring localized voltages on programmable integrated circuits

Abstract: A method is described for measuring localized operating temperatures and voltages on an integrated circuit. The integrated circuit includes an oscillator circuit with a frequency that varies with temperature and/or applied voltage. The frequency of the oscillator is then determined, using a constant voltage, for a number of temperatures to establish a known relationship between oscillation frequency and temperature. Once the relationship is known, a similar oscillator is included within or adjacent a second circuit of the integrated circuit. The operating temperature or operating voltage of the second circuit may then be determined by monitoring the frequency of the oscillator while the second circuit is operational.

Properties of an oscillator slaved to a periodically interrogated atomic resonator

Abstract: In advanced atomic resonators, such as those using a fountain of cold cesium atoms or an ensemble of stored ions, the atomic medium is interrogated periodically, and the control signal of the slaved oscillator is updated at equally spaced time intervals. We analyze the properties of the output frequency of these frequency standards. We establish the equations that describe the time behavior of this frequency. We give the stability condition and the transient response of the frequency feedback loop, the response to systematic frequency changes of the free running oscillator, the frequency stability for given free-running oscillator noise and given optical detection noise, and the limitation of the frequency stability by down-conversion of the intrinsic oscillator frequency noise (Dick effect). We point out that a second integration in the feedback loop may not improve significantly the rejection of slow perturbations, unless a condition relative to the timing of the atom-field interaction is verified.

Temperature compensated multi-channel, wavelength-division-multiplexed passive optical network

Abstract: Temperature compensation of a wavelength-division-multiplexed (WDM) passive optical network (PON) communication system uses power measurements from each of it remote nodes (RNs) to adjust the frequency of an associated multifrequency laser (MFL). Changes in the power level at each RN caused by frequency drift of its waveguide grating router (WGR), due to changes in the WGR temperature, is determined by monitoring the power level received at each RN and corrected by appropriate changes in the temperature of the associated MFL. The WGR uses one output port (e.g., channel 1 ) which is looped-back through the WGR a second time to increase the temperature sensitivity of the power measurements. A temperature-control algorithm controls the temperature of the MFL as a function of changes in the received power at the WGR.

Temperature insensitive silicon oscillator and precision voltage reference formed therefrom

Abstract: Micromachined, thermally insensitive silicon resonators are provided having accuracy equivalent or superior to that of quartz resonators, and are fabricated from a micromechanical, silicon-on-glass process. In one embodiment, such a resonator is realized using a tuning fork gyroscope (4). Radiation-hard precision voltage references (PVRs) are enabled using the silicon resonators. Thermal sensitivity is reduced relative to that of a silicon-on-silicon process oscillator, providing a thermal sensitivity comparable to that of a quartz oscillator. By employing a micromechanical device based upon a tuning fork gyroscope (4), resonators are made from either or both of the gyro drive and sense axes. A resonator constructed as an oscillator loop (8) whose resonant frequency is compared to a frequency standard provides a bias voltage as a reference voltage (Vref).

Automatic frequency control in FSK receiver using voltage window deviation

Abstract: An AFC circuit for controlling an oscillation frequency of a local oscillator is disclosed. An f/V converter converts a frequency of an FSK signal to a received signal voltage varying depending on the frequency of the FSK signal. A window generator generates a voltage window including a reference voltage corresponding to a center frequency of the FSK signal. The oscillation frequency of the local oscillator is controlled depending on a deviation of the received signal voltage from the voltage window so that the received signal voltage falls into the voltage window.

Communication device a frequency compensating synthesizer and method of providing same

Abstract: A communication device including a plurality of frequency synthesizers (24, 28, 30). At least one of the frequency synthesizers (24) is driven with a reference frequency from a crystal oscillator (58). The at least one frequency synthesizer (24) includes a phase locked loop with a fractional-N divider (48) which is programmed by a control circuit (64) to vary as a function of temperature compensation, frequency compensation, and a frequency multiplication factor. The output (46) of the at least one frequency synthesizer (24) is used to provide a compensated reference frequency input for the remaining frequency synthesizers (28, 30). The radio provides all the frequency synthesizers (24, 28, 30) with temperature and frequency compensation using a reference frequency from a crystal oscillator (58) and only one high resolution frequency compensating synthesizer (24).

Frequency band select phase lock loop device

Abstract: A multi-band phase lock loop (PLL) device for use in a communication system. The PLL comprises a frequency reference oscillator, a reference frequency divider, a phase and frequency detector, a filter and compensation circuit, a microcontroller, a multi-band voltage controlled oscillator (VCO), and a feedback divider. A fast feedback signal is provided to the VCO for phase locking operation. A slow feedback signal is used by the microcontroller to generate a frequency adjust signal for frequency band centering for the VCO. The microcontroller also controls the VCO to change the frequency band of operation. The PLL device may be used in a communication system that operate in both the cellular frequency band and the PCS frequency band.

High frequency Wien-type chaotic oscillator

Abstract: A Wien-type oscillator based on a current feedback opamp (CFOA) employed as a non-inverting voltage-controlled voltage source is modified for chaos by adding an inductor and a general purpose signal diode. By using a CFOA as the active element, high operating frequencies are possible. The chaotic oscillator is described by a fourth order system of differential equations. Experimental results, PSpice simulations and numerical simulation of the proposed model are included.

Adaptive filtering method and apparatus to compensate for a frequency difference between two clock sources

Abstract: Frequency differences between differing clock sources are compensated for by an adaptive filtering mechanism. An amount of frequency drift between two clock sources is determined. Then, based on that amount of frequency drift, a filtering value is selected to be used in tracking the frequency drift. If the frequency drift is determined to be large, then a minimum filtering value is selected. However, if it is determined to be small, then a maximum filtering value is selected. The selected filtering value is used to adjust the address(es) of one or more data bits being transmitted and received using the two clock sources, such that the frequency drift is properly tracked.

Method and apparatus for fine frequency synchronization in multi-carrier demodulation systems

Abstract: A method and an apparatus relate to a fine frequency syn-chronization compensating for a carrier frequency deviation from an oscillator frequency in a multi-carrier demodulation system of the type capable of carrying out a differential phase decoding of multi-carrier modulated signals, the sig-nals comprising a plurality of symbols, each symbol being defined by phase differences between simultaneous carriers having different frequencies. A phase difference between phases of the same carrier in different symbols is deter-mined. Thereafter, a frequency offset is determined by eliminating phase shift uncertainties related to the trans-mitted information from the phase difference making use of a M-PSK decision device. Finally, a feedback correction of the carrier frequency deviation is performed based on the deter-mined frequency offset. Alternatively, an averaged frequency offset can be determined by averaging determined frequency offsets of a plurality of carriers. Then, the feedback correction of the frequency deviation is performed based on the averaged frequency offset.

Temperature compensating circuit for a crystal oscillator

Abstract: An electrical device to compensate for crystal oscillator frequency shifts occurring over a temperature range includes a voltage divider for generating a temperature variable, compensation voltage at an output. The output of the voltage divider is to be electrically coupled to the oscillator so that the compensation voltage compensates for the crystal oscillator frequency shifts otherwise occurring over the temperature range. A voltage source is to be coupled to an input of the voltage divider for inputting a generally fixed voltage during normal crystal oscillator operation, and providing for multiple and repeatable adjustments to the fixed voltage before beginning the normal crystal oscillator operation.

Frequency synthesizer having a speed-up circuit

Abstract: It is an object of the present invention to provide a frequency synthesiser with a lock speed-up arrangement in a simple and effective form. In accordance with the invention there is provided a frequency synthesiser including a voltage controlled oscillator, a phase detector which receives a base frequency signal and a feedback signal derived from the output of the voltage controlled oscillator and a filter circuit connecting the output of phase detector to a frequency control voltage input of the voltage controlled oscillator, the filter circuit having a reference voltage connection, and a speed-up circuit for applying a voltage signal to the reference voltage connection when a frequency change is demanded.

Crystal oscillator having prestressing bias circuit to provide fast start-up

Abstract: A fast start-up oscillator has an oscillator for generating a signal having a desired frequency. A prestress biasing circuit is coupled to the oscillator. The prestress biasing circuit is used for prestressing a piezoelectric resonator of the oscillator and for placing a bias voltage on the oscillator after the piezoelectric resonator of the oscillator has been prestressed.

Dc offset compensation for zero if quadrature demodulator

Abstract: The present invention provides dc offset compensation circuit (800) for a zero IF FM quadrature demodulator in an AMPS cellular mobile telephone system. A frequency offset is introduced to remove modulation inherent dc components from supervisory audio tones and Manchester codes from a modulated signal. The local oscillator (608) is operated at a frequency that is slightly different, e.g. 5 kHz from a frequency which would mix down the intermediate frequency signal to zero. A dc offset is produced with a control loop to eliminate fixed dc components caused by leakage from a local oscillator (608). After a given time, the control loop may be frozen and the frequency offset of the local oscillator (608) can be removed.

Digital frequency generation method and apparatus

Abstract: A method and a circuit are described for generating a frequency signal having fine frequency control, and which are suitable for implementation on an-integrated circuit. The output frequency is generated having a controllable relationship with an oscillator frequency by using multiple phases of the oscillator signal. The output is provided by selecting a signal from the plurality of phases, and the frequency control is achieved by varying the selection cyclically, so that the output signal may be composed of segments of different phases. The cyclic selection is performed at a controllable rate to achieve stable generation of an original frequency signal.

Tunable oscillator using a reference input frequency

Abstract: A tunable oscillator includes an input for receiving an input signal from a source of precision frequency such as a CMOS quartz crystal oscillator. The tunable oscillator converts the frequency of the input signal to a first current using a frequency to current converter. The current produced is proportional to a first capacitor, C1. The first current is replicated to produce a subsequent current using a current mirror structure. The subsequent current is then used to generate a periodic signal using a current to frequency converter. The output frequency of the current to frequency converter is inversely proportional to a second capacitor, C2. As such the output frequency of the tunable oscillator is tunable by changing the value of the capacitance ratio C1/C2. The invention is suitable for applications that require a precision tunable source of frequency such as automated test equipment (ATE) and electrical instrumentation.

Multiple frequency band voltage controlled oscillator

Abstract: A radio frequency oscillator containing a means of frequency band selection and a tuning mechanism permitting frequency variation within each of the bands. The oscillator typically consists of a transistor, a frequency determining circuit, one or more voltage controlled variable capacitance diodes for frequency tuning and frequency range switching means to step change the operating frequency. The frequency determining circuit can consist of a lumped inductor, a microstrip line or a combination of a microstrip line and a lumped inductor. The frequency determining circuit is typically connected to the base of the transistor. In a preferred embodiment the frequency range switching is accomplished using an RF switching diode, used to short out one or more portions of the tuned microstrip line in accordance with the required frequency step change. The circuit also incorporates additional circuitry to support frequency modulation.

The modulational method of quartz crystal oscillator frequency stabilization

Abstract: A new trend in self-contained (without the use of quantum discriminators) frequency stabilization of an oven controlled crystal oscillator (OCXO) and frequency standard is proposed and discussed. The method developing the trend is called a modulational method and is based on the use of the reference properties of crystal resonator natural bulk vibrations (double-frequency and multi-frequency oscillators are not used in this case). The concept is based on dynamic modulation characteristics of an oscillator, and basic relationships are found for their calculation. The construction principles of the frequency control systems are formulated substantiating mathematically the essence of the method. Basic ratios of modulating signals are determined, the solution of which shows only a slight influence of the modulation signal on the Allan variance and spectral density of an OCXO. The results of the method's practical use are considered. Their subject is the OCXO with the oven system adapted to the ambient temperature and crystal frequency standard with aging rate compensation.

Method for realizing an improved radio frequency detector for use in a radio frequency identification device, frequency lock loop, timing oscillator, method of constructing a frequency lock loop and method of operating an integrated circuit

Abstract: An integrated circuit comprising a receiver, a transmitter, and a frequency lock loop configured to supply clock signals to the receiver and transmitter, the frequency lock loop including a current source having a thermal voltage generator, a current controlled oscillator having a plurality of selectively engageable current mirrors multiplying up the current of the current source, the frequency of the frequency lock loop varying in response to selection of the current mirrors, the current mirrors including transistors operating in a subthreshold mode. A method of operating an integrated circuit including a receiver, a transmitter, and a frequency lock loop configured to supply clock signals to the receiver and transmitter, the frequency lock loop including a current source having a thermal voltage generator, a current controlled oscillator having a plurality of selectively engageable current mirrors multiplying up the current of the current source, the frequency of oscillation of the frequency lock loop varying in response to selection of the current mirrors, the method comprising engaging selected current mirrors and operating transistors in the current mirrors in a subthreshold mode.

Dual band voltage controlled oscillator

Abstract: A voltage controlled oscillator operable on two widely separated frequency bands, such as 900MHz and 1.8 GHz for example. The voltage controlled oscillator includes two negative resistance generators (32, 34) which share a common tunable tank circuit (26) and a common impedance matched combiner circuit (28) which provides the RF output (36). The VCO uses no pin diodes which could degrade Q and phase noise, and the VCO uses only one varactor (30) to tune both frequency bands which reduces costs. Separate negative resistance generators (32, 34) are used to provide optimum frequency selectivity within each frequency band.

Oscillator circuit for a semiconductor memory having a temperature dependent cycle

Abstract: An oscilator circuit for a integrated circuit memory device to optimize the refresh operating circuit and suppress wasteful power consumption in which the oscillator frequency is set high during high temperatures and the oscillator frequency is set low during low temperatures. A current I 1 is generated by means of the current source 100 a having characteristics in which it is increased during high temperatures and decreased during low temperatures, and is supplied to the ring oscillator 200 . A current corresponding to the current I 1 is supplied to each inverter in the frame oscillator 200 , and since the oscillator frequency is controlled by means of the current value of the supplied current, the frequency of the clock signal CLK generated increases accompanying a rise in temperature, and since the refresh operation is conducted based on the clock signal CLK, the data holding capabilities can be ensured during high temperatures, wasteful power consumption can be reduced during low temperatures, and optimization of the refresh operating frequency can be realized.

Circuit for minimizing turn-on time of temperature compensated crystal oscillator

Abstract: A temperature compensated crystal oscillator with an improved phase noise characteristic and a fast start up time includes a large time constant low-pass filter coupled to a temperature compensation circuit. At start up the low pass filter is effectively bypassed to enable the temperature compensation voltage and oscillator output frequency to settle quickly. A capacitance in the low-pass filter is precharged by a precharge circuit to match the temperature compensation voltage without disturbing the temperature compensation circuit and the concurrent settling of the oscillator. When the capacitance is fully charged, the low-pass filter is enabled without unsettling the oscillator output frequency.

Extended frequency range relaxation oscillator with improved linearity

Abstract: A relaxation oscillator, such as a voltage controlled oscillator (VCO), with automatic swing control feedback which dynamically monitors the voltage swing across a capacitor and adjusts the oscillator threshold voltage, at which reversal of the polarity of the charging/discharging current occurs, to maintain the effective voltage swing at a constant level. The improved relaxation oscillator provides a very wide linear range of frequency variation versus control voltage (or current) and allows for the extendibility of linear operation to or near the maximum frequency that can be practically achieved by the oscillator circuitry.

Digital communication device

Abstract: Known is a digital communication device, such as a pager, with an AFC loop. In order to avoid erroneous tuning in such a receiver to a strong adjacent channel, frequency offset compensation should be done over a limited range. A robust AFC control loop is provided by separating short term and long term frequency drift. Herewith, optimal short term compensation can be done. Alternatively, cost reduction can be achieved by allowing greater temperature and aging drifts.

Transmit signal generation with the aid of a receiver

Abstract: A transceiver which generates transmit and receive channel frequencies using a single crystal reference oscillator is disclosed. A first and second local oscillator is connected to the crystal reference oscillator. A first down converter is connected to the first local oscillator which mixes a receive signal with a first local oscillator frequency to produce a first intermediate frequency signal. The first intermediate frequency signal is then amplified and filtered and applied to a second down convertor which mixes the filtered first intermediate frequency signal with a second local oscillator frequency to produce a second intermediate frequency. A transmit frequency offset is then generated using the second local oscillator frequency. A transmit frequency generator generates a transmit frequency using the transmit frequency offset and the first local oscillator frequency.

Coarse frequency synchronization in multicarrier systems

Abstract: A method and apparatus provide coarse frequency synchronization compensating for a carrier frequency deviation from an oscillator frequency in a demodulation system capable of demodulating a signal having a frame structure with at least one useful symbol and a reference symbol which is an amplitude-modulated sequence. A received and down-converted signal undergoes amplitude-demodulation to generate an envelope that is correlated with a predetermined reference pattern to determine the carrier frequency deviation. Finally, the oscillator frequency is controlled based on the carrier frequency deviation. The reference symbol may comprise two identical sequences. In this case, the envelope obtained by the amplitude-demodulation has two portions which are based on the identical sequences. One of the portions of the envelope is correlated with the other one of the portions in order to determine the carrier frequency deviation. The oscillator frequency is controlled based on the determined carrier frequency deviation.

Time division duplex transceiver utilizing a single oscillator

Abstract: A single voltage controlled oscillator (VCO) running at a closed loop controlled fundamental frequency whereby the harmonic products generated by the VCO are used for both transmission and reception. The use of a single VCO and associated supporting circuitry for both transmit and receive portions of the circuit serves to reduce the cost of the transceiver. The radio transceiver comprises a single synthesized oscillator having high harmonic content. The frequency conversions in the receiver make use of the harmonic frequency components of the same oscillator used in performing modulation during transmission.

Accurate frequency comparisons at the 1/spl times/10/sup -15/ level

Abstract: Increased fractional frequency uncertainties in comparing two cesium-fountain primary frequency standards due to a long-baseline comparison process are examined. These include frequency uncertainties introduced by the time-transfer process and uncertainties introduced by possible long-term dead time in the fountain operation. Using common-view GPS it may take up to 40 days to reduce the time-transfer fractional frequency uncertainty to 1/spl times/10/sup -15/ A combination of common-view GPS and two-way satellite time and frequency transfer can reduce this to 24 days. With a very low noise local oscillator such as a cavity-tuned hydrogen maser, distributed fountain dead times as large as 87% can be present and yet contribute only an additional uncertainty of less than 3.3/spl times/10/sup -16/.