Showing papers on "Frequency drift published in 1988"

High-performance crystal oscillator circuits: theory and application

Abstract: A general theory that allows the accurate linear and nonlinear analysis of any crystal oscillator circuit is presented. It is based on the high Q of the resonator and on a very few nonlimiting assumptions. The special case of the three-point oscillator, that includes Peirce and one-pin circuits, is analyzed in more detail. A clear insight into the linear behavior, including the effect of losses, is obtained by means of the circular locus of the circuit impedance. A basic condition for oscillation and simple analytic expressions are derived in the lossless case for frequency pulling, critical transconductance, and start-up time constant. The effects of nonlinearities on amplitude and on frequency stability are analyzed. As an application, a 2-MHz CMOS oscillator which uses amplitude stabilization to minimize power consumption and to eliminate the effects of nonlinearities on frequency is described. The chip, implemented in a 3- mu m p-well low-voltage process, includes a three-stage frequency divider and consumes 0.9 mu A at 1.5 V. The measured frequency stability is 0.05 p.p.m./V in the range 1.1-5 V of supply voltage. Temperature effect on the circuit itself is less than 0.1 p.p.m. from -10 to +60 degrees C. >

Direct conversion FM receiver with offset

Abstract: A direct conversion FM receiver that includes AC coupling and automatic gain control employs an offset frequency at the first local oscillator. The offset frequency prevents the frequency spectrum occupied by the signal modulation from being affected by AC coupling. The offset frequency is chosen so that it translates the frequency spectrum of the received signal outside the DC notch created in the spectrum by the AC coupling. To conserve battery supplied power, an error amplifier coupled between the output of the receiver and the first local oscillator maintains the offset frequency after it has been established by a frequency synthesizer, which is then turned off.

A fully integrated high-speed voltage controlled ring oscillator

Abstract: An N ring element ring oscillator merged with an M element ring oscillator by using a linear combining circuit. By adjusting the control voltage, the oscillation frequency can be varied from 1/2*N*T d (where T d is a gate delay) to 1/2*M*T d . Other embodiments provide extended frequency tuning range.

Integrated circuit random number generator using sampled output of variable frequency oscillator

Abstract: An integrated circuit random number generator which uses a triangular output analog oscillator to vary the frequency of a higher frequency voltage controlled oscillator. The output of the voltage controlled oscillator is sampled at a rate much less than the rate of oscillation of the voltage controlled oscillator to produce random digital values.

Apparatus and method for detecting small changes in attached mass of piezoelectric devices used as sensors

Abstract: In analysis, particularly for medical diagnostics, material can be selectively bound to the surface of a piezoelectric crystal by a reagent. The amount of material so bound affects the speed of propagation of an acoustic wave launched and received on the crystal surface by respective electrode pairs. Previously the crystal was used as a resonant element in an oscillator controlling the frequency of oscillation and so indicating the amount of bound material. However, the oscillator was either unstable or the range of bound masses too small to be of practical use. In the present invention delay between launch and reception of the acoustic wave provides a control signal for a voltage controlled oscillator. A much more stable system can therefore be constructed with a wide working range and high stability since the crystal is no longer the resonant element. Much greater sensitivity is also possible since the oscillator frequency may be greatly increased. A control signal representative of delay may be produced by a phase comparator comparing the phase of two input signals: one direct from the oscillator, and one from the reception of an acoustic wave on the crystal surface launched using a signal from the oscillator. The signal to the crystal may be modulated using a low frequency oscillator before it reaches the crystal to aid the oscillator in following frequency changes due to changing crystal surface conditions and the resulting signal may be summed with the output of a resonance oscillator before application to the crystal to aid the oscillator in initially settling to a stable frequency.

Ultrasonic oscillation circuit

Abstract: A circuit for generating a driving signal for an ultrasonic vibrating element including a voltage controlled oscillator for generating an oscillation signal which is supplied to the ultrasonic vibrating element as the driving signal, a phase difference detector for detecting a phase difference between the voltage and the current of the driving signal to produce a control voltage corresponding to the detected phase difference, said control voltage being applied to a control input of the voltage controlled oscillator, a comparator for comparing the control voltage from the phase difference detector with a reference voltage to generate an output signal when the control voltage exceeds the reference voltage, and a voltage setter for responding to the output signal to reset the oscillation frequency of the voltage controlled oscillator to a predetermined frequency which is lower than the optimum resonance frequency so that the ultrasonic vibrating element is energized in the most efficient manner.

Signal analyzer apparatus with automatic frequency measuring function

Abstract: In a siganl analyzer apparatus, a signal received while a local oscillator is swept in a analog manner is selected and detected by an IF circuit using a desired RBW, and the resultant data is stored in a memory and displayed on a display unit. A sweep signal generator controls the local oscillator in an analog manner such that frequency measurement can be performed within a desired measuring frequency range. A peak search section outputs a frequency valve corresponding to the maximum value of the data in the memory. A discriminator compares the span set in the sweep signal generator with the resolution bandwidth set in the IF circuit, when a frequency is measured using the desired span, and outputs the obtained value. A frequency controller causes the sweep signal generator to perform sweeping/measurement by setting a frequency detected by the peak search as a center frequency, and by using a span narrower than that used in the previous measurement cycle, on the basis of the comparison result from the discriminator. A frequency measuring section measures the frequency of an input signal using the output frequencies from the local oscillator and the IF circuit, on the basis of the comparison result from the discriminator, when the frequency controller causes the sweep signal generator to perform frequency measurement by minimizing the span.

Integrator controlled time compensated clock oscillator

Abstract: A time compensated clock oscillator (TCCO) is provided with an integrator to produce stability of the output frequency. The integrator is connected between the D/A converter and the voltage controlled crystal oscillator (VCXO) of the TCCO. The output frequency of the VCXO is fed back to a frequency counter, which samples the output, determines its average frequency, and compares it with a reference frequency. A microprocessor corrects the reference frequency for temperature changes, determines the output frequency error, calculates the output frequency drift rate, and provides a digital correction signal. The D/A converter converts the digital correction signal to an input voltage for the integrator. The integrator produces a ramp-shaped control voltage for input to the VCXO. Because the control voltage produced by the integrator changes smoothly over the interval between samples by the frequency counter, the output frequency drift rate of the VCXO is continuously corrected to produce improved short-term frequency stability.

Process and apparatus for phase-regulated power and frequency control of an ultrasonic transducer

Abstract: A phase-regulated power and frequency control of an ultrasonic transducer which is supplied by a variable frequency oscillator of a phase control circuit with a plurality of voltage pulses amplified by a driver. First the variable frequency oscillator is canned to find a resonance frequency of the ultrasonic transducer and the scanner is locked to the resonance frequency of the ultrasonic transducer after locking into the phase control circuit. After initial oscillation of the ultrasonic transducer in the vicinity of a series resonance frequency thereof a capacitive phase angle between voltage and current is introduced and is maintained operationally so that by phase control of the phase control circuit the operating frequency of the oscillator is reduced relative to the series resonance frequency of the transducer. A phase angle change as a result of mechanical loading of the transducer leads to an increase of the operating frequency of the oscillator and thus to a shift toward the series resonance frequency of the transducer.

Variable frequency light source

Abstract: PURPOSE:To assure a variable frequency light source excellent in frequency accuracy and long-time stability with a simplified structure by changing an oscillation frequency of a semiconductor laser by changing a frequency of an oscillator. CONSTITUTION:A switch 14 is shifted from the side (a) to the side (b) when the oscillation frequency of a semiconductor laser makes coincidence with one frequency at a point P among peaks of transmission characteristics of a Fabry-Perrot interferometer 6. Modulation frequency f1 is here assumed f1L. An output from an optical detector 9 is subjected to synchronous detection with a frequency f1 signal in a synchronous rectifier circuit 131. The output is proportional to a frequency difference between FM sub-carriers 22, 23 and the transmission peak through the Fabry-Perrot interferometer 6. Accordingly, with such a difference, a control section 132 controls an injection current into the semiconductor laser 1 such that said difference is zero. Hereby, the emission frequency of the semiconductor laser 1 is changed and the transmission peak of the Fabry-Perrot interferometer 6 is forced to follow the just- mentioned change of the emission frequency by first control means 10. Thus, FSR makes coincidence with the modulation frequency f1. In the above operation, the number (m) of modes of the Fabry-Perrot interferometer 6 is evaluated according to the formula I and the laser oscillation frequency f0 is continuously changed according to the formula II by changing f1.

Center offset microwave frequency synthesizer

Abstract: An improved microwave frequency signal source using a single frequency offset technique which increases the frequency range of an indirect frequency synthesizer to twice the highest operating frequency of the programmable digital frequency divider in the loop includes a voltage-controlled oscillator (VCO) operating within a predetermined microwave frequency band and phase-locked to a reference oscillator operating at a reference frequency below microwave frequencies. The offset loop signal is developed by heterodyning the voltage-controlled oscillator (VCO) output signal with a microwave signal whose frequency is located at the center of the predetermined microwave frequency band of the VCO to form a signal at an intermediate frequency (I.F.) within the frequency range of a programmable digital frequency divider.

Tracking receiver for broadband chirp emissions

Abstract: A tracking receiver is disclosed which utilizes optical processing for detecting and tracking input broadband chirp like emission signals. The tracking receiver includes a scanning local oscillator, the output signal of which is caused to be scanned in frequency. A mixer mixes the unknown input signal and the local oscillator output signal to produce an intermediate frequency (IF), frequency difference signal. The IF signal is analyzed in an optical spectrum analyzer which includes an acoustooptical modulator for modulating a beam of radiation, as a laser beam, with the intermediate frequency signal, and optical means, as a lens, for producing a spatial frequency distribution of the intermediate frequency spectrum in a Fourier plane. A photodetector array is provided in the Fourier plane for detecting the spatial spectrum. A processor processes the output of the photodetector for temporally stable grouped intensity patterns caused by an input spectra signal varying in frequency near the scan rate of the local oscillator. The processor is responsive thereto to control a programmer which controls the frequency of the local oscillator to cause it to approach and become equal to the frequency of the input spectra signal. A recorder is provided for recording the output of the scanning local oscillator, and the scanning local oscillator is controlled to proceed through a programmed frequency scan pattern.

Multiband radar detector

Abstract: The invention concerns radar detectors which are capable of monitoring at least two frequency bands. A broad band antenna is provided, together with a mixer comprising an anti-parallel pair of diodes, and at least one local oscillator. The local oscillator frequency is mixed with radar frequency from the antenna to produce an intermediate signal which is amplified further down converted detected and fed to signal processing circuitry to actuate an alarm when radar frequency of interest is detected. The most effective mixing with the RF input takes place at twice the local oscillator frequency. By application of direct current bias to the mixer, the most effective mixing with the RF input is changed to occur at the local oscillator frequency. The local oscillator is used to monitor two different radar frequencies by application and non-application of DC bias to the mixer. For multiband detectors, more than one local oscillator may be used.

Frequency-doubling oscillator, tuned by varactors

Abstract: An ultrahigh-frequency oscillator. To double the frequency of an oscillator having a single field-effect transistor (10), whose fundamental frequency is adjusted by an impedance of gate (13) and an impedance of source (15), a filter (16+17) is mounted between the drain of transistor (10) and the ground. This filter, formed by a self-induction coil (16) in series with a varactor (17) is adjusted to the fundamental frequency: it assures the rejection, and favors the generation of the second harmonic, at double frequency. Application to ultrahigh-frequency sources.

Excitation supply for gas discharge tubes

Abstract: The present invention uses a variable frequency oscillator to drive a primary resonant converter output transformer circuit for exciting gas discharge tubes. The combination of the impedance of the resonant conversion circuit along with the impedance of the driven gas discharge tube taken in combination with the frequency of the variable oscillator will determine the output voltage of the circuit. By varying the frequency of the oscillator, the optimal output voltage and hence the optimal brightness of the gas discharge tube may be selected. At the optimal output voltage, the frequency of the switching supply may create an undesirable or desirable "bubble effect" in the gas discharge tube. An optional secondary frequency may be combined with the frequency of the variable frequency oscillator to create or eliminate the bubble effect according to the esthetic desires of the user.

A 300-MHz digitally compensated SAW oscillator

Abstract: A method for compensating for the inherent temperature sensitivity of surface-acoustic-wave (SAW) oscillators is described. Results for a 300-MHz digitally compensated SAW oscillator (DCSO) show a reduction of temperature-induced frequency variation from +or-125 parts per million to +or-1.4 parts per million over the temperature range of -23 to 75 degrees C. This is accomplished using simple digital circuitry and microprocessor control. The temperature-sensing scheme, using a SAW structure with two delay paths of different temperature sensitivity on the same AT-cut quartz substrate, virtually eliminates thermal resistance and time-constant problems. Advantages over ovenized systems include fast warmup; reduced size, weight, and power dissipation; low cost potential; and the ability to compensate for other sources of frequency drift. >

Frequency Stabilization Of A Diode Laser To A Fabry-Perot Interferometer

Abstract: A commercial GaAIAs diode laser is frequency locked to a Fabry-Perot interferometer. The temperature stabilization loop of this diode laser system maintains the relative frequency stability within 11 kHz. When the frequency control loop is closed, the relative frequency stability is improved to 450 Hz. A previously neglected frequency offset is also analyzed. This offset is a result of the injection current modulation technique commonly used to frequency lock diode lasers. The calculated frequency offset in our system is 150 kHz.

Method and apparatus for frequency modulation stabilization of a laser

Abstract: A microwave oscillator frequency modulates the output of the laser system to be controlled. The modulated output passes through a molecular gas cell. The output of the molecular gas cell is detected by a square law device, which produces a signal at the desired microwave frequency only when a sideband of the modulated laser output coincides with the desired molecular transition frequency. A quadrature signal pair is produced by mixing the filtered output of the square law device with two phase-shifted signals from the microwave oscillator. The dispersion signal can be used to control the output frequency of the laser system, since its magnitude and sign are uniquely related to the required direction of correction.

Method and apparatus for frequency control of multiple oscillators using a single frequency-locked-loop

Abstract: Frequency control of multiple oscillators using a single frequency locked loop is accomplished by a single frequency-control device that is time-shared with a plurality of voltage-controlled oscillators and selectively establishes a "desired" frequency for each oscillator. The output of each oscillator is, in turn, selectively routed to a frequency counter which measures the "actual" frequency of the oscillator. A comparison between the desired frequency and the actual measured frequency for each oscillator is made, and an error voltage developed. This error voltage is routed to the appropriate capacitor, which stores the voltage required to keep the selected oscillator on frequency until the next time it is measured.

Radio communication apparatus free from interference between local signal and transmission signal

Abstract: A radio communication apparatus capable of carrying out transmission and reception of signals at a time has a frequency synthesizer and a frequency modulator both in novel structures for removing interference between a local signal and a transmission signal. The frequency synthesizer has a local oscillator controlled by a first phase comparator for phase-comparing a frequency divided output of the local oscillator and a reference frequency signal to provide a local signal. The frequency division of the output of the local oscillator is effectd by a first frequency divider for dividing the frequency of the output of the local oscillator and a variable division ratio frequency divider for dividing the frequency of the output of the first frequency divider. The frequency modulator has a transmission oscillator controlled by a second phase comparator for phase-comparing the output of the first frequency divider and a frequency divided output of the transmission oscillator to provide a transmission signal. The frequency division of the output of the transmission oscillator is effected by a second frequency divider.

Digitally temperature-compensated oscillator

Abstract: A digitally temperature-compensated oscillator has an oscillator for producing a frequency signal, a regulator for regulating the frequency of the frequency signal, and a detector for detecting ambient temperature and producing a corresponding temperature signal. A processor processes the temperature signal with reference to the frequency signal to produce processed temperature data. A memory stores compensation data effective to regulate the frequency of the frequency signal. A controller operates according to the temperature data to retrieve corresponding compensation data from the memory for controlling the regulator according to the retrieved compensation data to regulate the frequency of the frequency signal.

Tuning system with provisions for calculating the local oscillator frequency from an aft characteristic

Abstract: A television tuning system includes control apparatus for changing the frequency of a local oscillator signal during a search and a comparator arrangement for determining when an AFT signal traverses first and second threshold values corresponding to first and second frequencies in respective "hump" regions of the AFT signal. The frequency of the local oscillator is set to the average of the first and second frequencies in order to set the frequency of the IF picture carrier closer to the nominal value than the first and second frequencies.

Common bus multinode sensor system

Abstract: The present invention is a multimode sensor system that transmits power down a common bus coaxial cable typically using an alternating current power source. Each remote unit connected to the coaxial cable and through an isolation transformer converts the alternating current power to direct current power for an integrated circuit bus interface. The interface is connected to the sensors. The interface is externally pin programmable to provide a carrier at a frequency for a channel assigned to the remote unit. The carrier is provided by a ripple counter producing a frequency divided signal compared to a fixed reference frequency, where the result of the comparison controls a voltage controlled oscillator. When plural low frequency analog signals are to be transmitted over the common bus, an on-chip multiplexer multiplexes the signals to an off-chip, external analog-to-digital converter. The analog-to-digital converter loads an on chip parallel to serial register that applies each bit of the sampled signal serially to an on chip Manchester encoder. The encoder modifies the input voltage of the voltage controlled oscillator operating at the carrier frequency. The oscillator signal is applied to the coaxial cable. Receivers at the end of the coaxial cable are each tunable to a designated carrier frequency and each decode the respective encoded signal. If a high frequency analog signal is supplied to the voltage controlled oscillator, the carrier is modulated by the high frequency signal and the receiver demodulates the signal. The integrated circuit is arranged so that the digital circuitry is generally isolated from the analog circuitry so noise immunity is enhanced.

Phase locked loop with self-adjusting circuit for oscillator working point

Abstract: A self-adjusting phase lock circuit including a frequency and/or phase comparator which compares the frequency and/or phase of a reference signal FVCO with the frequency and/or phase of a frequency or phase modulated signal RD generates an error signal which is applied as an input to an integrating network. The network generates an error voltage VC related to the frequency/phase error of the two signals which is applied to the control input of a voltage controlled oscillator operative to generate the reference signal FVCO as a function of the error voltage and of an adjusting voltage received at an adjusting input of the oscillator. Self-adjusting means is provided which includes a fixed reference voltage periodically applied as an input to the control input of the oscillator as a substitute for the error voltage and a source of a fixed frequency signal periodically applied as an input to the comparator as a substitute for the modulated signal RD. An operational network generates from the error voltage VC, a feedback signal (VRANGE) which is periodically applied to the adjusting input of the oscillator and held at said input by sample and hold circuits so that the adjusting voltage VRANGE is periodically adjusted automatically to maintain the phase lock circuit in an operative condition permanently close to a nominal working point independently of thermal drift and the performance spread of the components used.

High frequency multi-electrode linear accelerator

Abstract: PURPOSE: To simplify the structure and reduce the cost by allowing the frequency of high-frequency power introduced to make followup after variation in the resonance frequency of an acceleration cavity. CONSTITUTION: An accelerator according to existing invention consists of a high frequency power generating means (voltage control oscillator 15 and power amplifier 10) which varies its output frequency according to input signals, a frequency difference sensing means (phase detector 13 and amplifier 14) to sense the difference of the output frequency from the first named means from the actual resonance frequency of an acceleration cavity 1 and supplies this output from sensing as an input signal to the high frequency power generating means. The frequency of the high frequency power introduced into this acceleration cavity 1 is so formed as to follow up its resonance frequency. Accordingly, when the resonance frequency is varied by thermal deformation, etc., of the cavity 1, the output from sensing given by the frequency difference sensing means will vary, and the frequency of the high frequency power from the high frequency power generating means will vary in following-up thereto. This enables resonance without keeping constant the resonance frequency of the cavity 1, which eliminates use of any side tuner. COPYRIGHT: (C)1989,JPO&Japio

Smart sweep apparatus for data rate receivers

Abstract: Apparatus is provided for locking onto a severe doppler shifted data modulated carrier signal. A phase lock loop of the type having a data detection branch, a carrier tracking branch and a voltage controlled oscillator branch is modified to provide a summing circuit at the input of the voltage control oscillator in the voltage controlled oscillator branch. A sweep control circuit is connected to the input of the summing circuit for sweeping the voltage controlled oscillator through a range of frequencies which encompass the doppler shifted carrier frequency. An automatic frequency control circuit is connected to the input of the summing circuit for automatically disconnecting the sweep control circuit from the summing circuit when the frequency of the voltage controlled oscillator reaches a predetermined value defining a window which encompasses only the center frequency of the doppler shifted carrier frequency. The automatic frequency control circuit is adapted to drive the output of the voltage controlled oscillator to the center frequency of the doppler shifted carrier frequency without overshoot and then enable the phase lock loop to phase lock onto the phase of the doppler shifted carrier frequency to provide a locked on condition.

Method and circuit for trimming the frequency of a frequency source

Abstract: In order to adjust the frequency of an oscillator in a substation of a network to a reference frequency of the network, a reference station is provided with a high precision oscillator which is connected to a clock input of a counter If this counter has a defined counting state, a start signal is generated and transmitted to said substation At another defined counting state a stop signal is generated and transmitted to said substation In the substation the oscillator to be adjusted is connected to a local counter, which counts the pulses of the oscillator between said start and stop signals The count of this counter then is used as a measure for the frequency deviation of the oscillator and can be used for generating a control signal to adjust the frequency of the oscillator of the substation

Voltage control oscillator with modulation compensation

Abstract: An improved voltage controlled oscillator (VCO) is provided whereby the control voltage is utilized for modulation compensation by a modulation compensation network (90). The modulating signal is variably coupled into the voltage controlled oscillator (70) to compensate for the variation in the VCO's gain factor to yield a constant modulation level over a frequency band.

Sensitivity simulation results for a direct-conversion FSK receiver

Abstract: Results of computer simulation of a direct-conversion FSK (frequency-shift keyed) receiver are reported. The demodulation sensitivity depends strongly on the characteristics of the channel and postdetection filters. The sensitivity is defined as the Eb/No ratio at a bit-error rate of 10/sup -2/. The authors evaluated the dependence of the receiver sensitivity for bandwidth, section order, and filter type as parameters. Sensitivity degradation caused by the local frequency drift was determined. A phase detection technique for this type of receiver, which improves the sensitivity by 2 dB, is proposed. >

Effect of reflections on the drift characteristics of a fiber-optic passive ring-resonator gyro.

Abstract: We show the effect of reflections at the fiber ends on the drift characteristics of a fiber-optic passive ring-resonator gyro. A rotation-detection sensitivity as low as 3 × 10−5 rad/sec (τ = 30 sec) was obtained by reducing the effect of reflected lights with an optical phase modulator.