Showing papers on "Frequency drift published in 1991"

Offset frequency converter for phase/amplitude data measurement receivers

Abstract: An offset frequency converter (10) for the intermediate frequency (IF) stages of a multi-channel radio frequency (RF) phase/amplitude measurement receiver (8). The converter allows use of noncoherent transmitter and receiver local oscillator sources which utilize digital frequency synthesizers and enables harmonic mixing to be employed. The converter samples an incoming first intermediate frequency signal IF1 in a reference channel (38b). The IF1 sample is then upconverted to a higher frequency, filtered and downconverted to an IF1+IF2 signal offset from the IF1 sample by a lower second intermediate frequency IF2. The added frequency offset IF2 is derived from a time stabilized source independent of the transmitter but coherent with the receiver LO. The mixed IF1+IF2 signal is heterodyned with signals in both the signal channel (38a) from the antenna under test and the reference channel to obtain coherent outputs at IF2 which differ by phase and magnitude corresponding to the characteristics of the antenna under test.

High-speed voltage-controlled oscillator with quadrature outputs

Abstract: A voltage-controlled oscillator topology is described that combines a fully-differential four-stage ring oscillator with a balanced exclusive NOR gate frequency doubler, and provides both inphase and quadrature output signals at twice the ring oscillator frequency. These quadrature signals have a period of only four gate delays, which implies high frequency operation.

Digital temperature-compensated oscillator

Abstract: A digital temperature-compensated oscillator comprises a crystal oscillator, a first memory previously storing digital temperature compensation data obtained by previously measuring the relation between the ambient temperatures and the frequency deviations of the crystal oscillator, a second memory for storing frequency offset amounts of the oscillation frequency of the crystal oscillator, a temperature sensor for outputting analog detection data relating to the ambient temperature, an A/D converter for converting the analog detection data to digital detection data, a readout circuit for reading out temperature compensation data corresponding to the digital detection data and stored in the first memory according to the digital detection data and reading out the frequency offset amount stored in the second memory according to the digital detection data, an operation circuit for effecting the following calculation by use of the readout temperature compensation data and readout frequency offset amount to derive digital control voltage, V.sub.c =V.sub.co +(K.sub.00 +V.sub.co K.sub.10 +K.sub.01 T)×(ΔF+ΔF 2 ×K 10 /2) where K 00 , K 01 and K 10 are constants, V co is an initial value of the control voltage, T is an ambient temperature and ΔF is a frequency offset amount, a D/A converter for converting the digital control voltage into an analog control voltage, and a voltage-capacitance converter for receiving the analog control voltage and generating a control signal to be supplied to the crystal oscillator according to the received analog control voltage, wherein the frequency of the crystal oscillator is controlled according to the control signal.

Digital radio frequency compensation

Abstract: A frequency compensation voltage system in a mobile station of a digital packet radio system is used to modify the output frequency of the mobile's crystal controlled reference oscillator. A burst transmitted by a base station is received by the mobile and, once it is determined that the burst came from the correct base station, the frequency of the burst is compared to that of the reference oscillator. Stored voltage values corresponding to temperature, aging and tuning voltage compensation values are modified to conform the frequency of the mobile's reference oscillator to that of the burst received from the base station.

Differential-logic ring oscillator with quadrature outputs

Abstract: A topology for a high speed voltage controlled oscillator (VCO) with quadrature outputs is produced utilizing four inverting differential circuits (12, 14, 16, 18). The fully differential four stage ring oscillator has outputs from alternate delay circuits combined in balanced exclusive OR gate frequency doublers (24, 26) to provide both in-phase and quadrature output signals at twice the ring oscillator frequency. The period of the quadrature delay signals is four gate delays and is easily realized in the Ghz frequency ranges. The in-phase and quadrature output signals are again combined in a balanced exclusive OR gate frequency doubler (36) to obtain a final output frequency quadruple the ring oscillator frequency.

Phase locked loop circuit responding to supplied signal frequency

Abstract: A phase locked loop circuit, which is arranged for receiving a first signal having a given frequency and producing a second signal which has the same frequency and is synchronous with the first signal, comprises control voltage generating means for generating a control voltage responding to a phase difference and a frequency difference between the first and second signals, a voltage controlled oscillator containing a ring oscillator having a multiplicity of the rows of inverters for producing a frequency output which is primarily determined by the control voltage, and a quantity-of-rows changing means for automatically changing the quantity of the inverters rows in the ring oscillator according to the control voltage.

Method of realigning the local oscillators of a receiver and device for implementing the method

Abstract: The present invention relates to a method of realigning the local oscillators of a receiver, as well as a device for implementing the method. In a receiver with a high frequency/intermediate frequency translation oscillator, an intermediate frequency/baseband translation oscillator, and a sampling oscillator receiving a signal modulated by at least one circuit for inverse fast Fourier transform FFT -1 computation according to a multicarrier modulation of OFDM (Orthogonal Frequency Division Multiplexing) type with addition of a transition interval at the start of each transmission interval. The spectrum of the signal has two master lines with a fixed frequency difference between them. The method is characterized by the following steps: (1) determination of the start of a transmission interval; (2) determination of the position of the two master lines; and (3) computation of the variation of the phases of these two lines as a function of time, and exploitation of the result to set the frequency of the sampling oscillator and of the intermediate frequency baseband translation oscillator. The invention will find particular application to digital television.

Control of long‐term output frequency drift in commercial dye lasers

Abstract: A simple technique using a scanning confocal Fabry‐Perot etalon and a stabilized helium‐neon laser is described that can be used to correct the long‐term drift in output frequency of actively stabilized commercial dye lasers. Using this technique the long‐term drift in the ultraviolet output frequency of an intracavity‐doubled Coherent Inc. CR699‐21 ring dye laser has been reduced to ≲±2 MHz.

Switching regulator in which oscillation is maintained below a predetermined frequency

Abstract: A switching regulator, which applies output DC voltage to a load via an oscillator oscillatable between ON and OFF states, has an oscillation controller to control the oscillation of the oscillator based on the load so that a frequency of the oscillating of the oscillator is kept lower than a predetermined frequency irrespective of the load.

Electrically tuned RF receiver, apparatus and method therefor

Abstract: An electrically tuned super-regenerative receiver (10) comprises a feedback type oscillator having a signal output and a signal input, phase shift components (30) connected in a feedback loop for coupling the signal output to the signal input to cause oscillations, and a quench oscillator (35) coupled to the signal input for switching the oscillator between an oscillating and a non-oscillating condition. A variable capacitance device (40), such as a varactor diode, is connected between the signal output and a reference potential (21), and a microprocessor (105) provides a tuning voltage (42) which is applied at the signal output for varying the current in the varactor diode, thereby varying the oscillator center operating frequency. The oscillator center operating frequency is detected by a spectrum analyzer (112) and compared to a desired center operating frequency by a controller (118). The controller controls a signal generator (123) to transmit a control signal which is received by the receiver and provided to the microprocessor for varying the tuning voltage to change the oscillator center operating frequency to be equal to the desired center operating frequency. An EEPROM (108) is provided for storing the tuning voltage required to produce oscillations at the desired center operating frequency.

Wideband oscillator with bias compensation

Abstract: An RF oscillator is disclosed that can be tuned to operate over a wide range of frequencies while maintaining advantageous bias conditions. The oscillator includes circuitry that adjusts an oscillator bias signal in response to changes in oscillator frequency and/or ambient temperature, and does so without resort to using the same signal for both bias and frequency control. By so doing to control parameters such as phase noise, output power and compression angle, both the frequency range and temperature range of an oscillator can be extended, while simultaneously improving the oscillator's performance.

Circuit for phase locking an oscillator within any one of a plurality of frequency ranges

Abstract: An adaptive oscillator control system for use in television receivers or monitors includes a phase locked loop together with a static phase error correction system which responds to long term error signals of significant magnitude within the phase locked loop to adjust the free-running frequency of the oscillator. An oscillator range control includes a processor having a plurality of established oscillator frequency ranges which are identified by oscillator range code numbers. A measuring counter and clock circuit cooperate to count the number of clock signals occurring during the horizontal sync reference signal period to establish a frequency reference number. A first frequency approximation is provided based upon the oscillator range code number or a known standard scan frequency. A frequency detector examines the oscillator output and provides a second frequency approximation to adjust the oscillator frequency until it falls within the appropriate frequency range. A confidence circuit examines the consistency of oscillator frequency maintenance within the appropriate frequency range and upon establishing the desired confidence level enables the phase locked loop to provide synchronization. Thereafter, a lock detector responds to the occurrence of frequency and phase lock by the phase lock loop to enable the static phase error corrector and deactivate the oscillator range control system. The lock detector upon detecting horizontal synchronization, for broadcast type video, increases the second frequency approximation range.

Voltage controlled oscillator with correction of tuning curve non-linearities

Abstract: A scanning-superhetrodyne ESM receiver having a VCO for a local oscillator which is linearized and temperature compensated. A stable combline oscillator is used to generate known frequency signals which are frequency converted to an intermediate frequency (IF) using the local oscillator and frequency converter(mixer). The frequency of each combline signal is measured and a table of known voltage/frequency points is generated. The table is input to a Cubic Spline program which computes the coefficients for the best-fit third order polynomial for each pair of data points. When a particular local oscillator frequency is desired, the corresponding tune voltage is computed by solving the polynomial equation for the given frequency range. By repeating the calibration on a periodic, or an "as needed" basis, temperature compensation is achieved.

PLL including static phase error responsive oscillator control

Abstract: A static phase error responsive oscillator control includes a phase detector coupled to a source of horizontal synchronizing pulses, a low pass filter, an error amplifier, a voltage controlled oscillator having a frequency equal to a multiple of the horizontal scan frequency, and a corresponding frequency divider. A threshold detector responds to error signals in excess of predetermined upper and lower thresholds to indicate large magnitude frequency corrections. An averaging circuit determines the long term character of the large magnitude corrections to alter the free-running or static frequency of the oscillator. Once the free-running frequency is corrected, static phase error is substantially reduced or eliminated.

Method for resetting the local oscillators of a receiver and device for implementing such method

Abstract: Receiver comprising a high frequency-intermediary frequency transposition oscillator, an intermediary frequency-base band transposition oscillator, a sampling oscillator and receiving a signal modulated by at least one circuit for the inverse rapid Fourier transformed calculation FFT-1 according to a multicarrier modulation of the type OFDM (Orthogonal Frequency Division Multiplexing) with addition of a transition interval at the beginning of each emission interval, the spectrum of said signal including two pilot spectral lines presenting between each other a fixed frequency difference. The method is characterized by the following steps: 1) determination of the beginning of an emission interval; 2) determination of the position of the two pilot lines; 3) calculation of the variation of phases of said two lines as a fonction of time and exploitation of the result in order to adjust the frequency of the sampling oscillator and of the intermediary frequency-base band transposition oscillator. Application to digital television.

A model for the frequency fine structure of auroral kilometric radiation

Abstract: A model for AKR frequency fine structure in which the fine structure is a natural consequence of the emission of electron cyclotron maser radiation in a nonuniform magnetic field is presented. The model is examined by using 1D electromagnetic particle-in-cell simulations. It is found that maser radiation is emitted as individual wave packets combine to form the drifting emission features that make up the fine structure. Rising frequency drifts are associated with wave packets emitted independently of one another. Wave packets that interact with one another produce features with falling frequency drift. The emission features produced have a large spread in both positive and negative frequency drift rates. The average positive drift rate of rapidly drifting features is found to be approximately proportional to the maser growth rate.

Adjustable bandwidth in a radiotelephone

Abstract: The frequency of a first local oscillator signal (1.LO) is offset in reference to the center frequency of a first bandpass filter (4), and the frequency of a second local oscillator signal (2.LO) is offset in reference to the center frequency of a second bandpass filter (7). The frequency offsets are selected so that only a portion (x, y) of the filter (4, 7) bandwidths (bw, BW) will add to an "imaginary" effective narrow bandwidth (NBW). The amounts of frequency offset are continuously adjustable by programmable controller.

On channel agile FM demodulator

Abstract: An on channel frequency agile PLL demodulator is provided using a precise and stable oscillator (82), such as a VCXO having its output frequency variable over a limited range. The output of the oscillator is multiplied (84) by a multiplication factor to produce a mixing frequency. The multiplication factor scales the limited range of the oscillator to produce a proportionate mixing frequency deviation. A frequency synthesizer (90) is used to enable the demodulator to detect signals on different channels. In one embodiment, the output of the frequency synthesizer (90) is mixed with the scaled oscillator output to provide a mixing frequency (fn) having a fixed deviation for all channels.

Voltage controlled oscillator employing negative resistance

Abstract: A voltage controlled oscillator circuit has been provided that allows for varying the center frequency of oscillation through an applied voltage signal (V F ). Further, the center frequency of oscillation can be fine tuned around the center frequency via a modulation signal (S M ). The voltage controlled oscillator circuit utilizes a negative resistance technique for oscillation and includes an output amplifier whose output resistance can be adjusted to match the input impedance of another circuit for maximum drive capability.

High speed automatic frequency tuning method

Abstract: A high speed automatic frequency tuning method for tuning a broadcasting frequency of a channel selected by a viewer is disclosed. For this, the high speed automatic frequency tuning method moves a tuning control frequency in one direction of the high or low band directions of the reference search frequency, according to the magnitudes between the reference search frequency and the active broadcasting frequency, thereby searching the broadcasting frequency.

High-frequency voltage controlled oscillator

Abstract: A voltage controlled oscillator provides a trimming stub (3) for adjusting a free-running frequency in parallel to a microstrip line resonator (4) This arrangement makes it possible to easily perform fine adjustment of a free-running frequency used in the voltage controlled oscillator capable of supplying 2 GHz or higher oscillating frequency

Estimating of steady state voltage and frequency of power systems from digitized bus voltage samples

Abstract: This paper presents a new efficient technique for estimating the voltage and frequency of power systems from digitized bus voltage samples. The new algorithm is based on the least absolute value error (LAV) approximation technique. The proposed algorithm is superior to the well-known least error squares technique (LS) used in Ref. 1, when the voltage samples contain bad data or noise in instrumentation and telemetry. The algorithm was tested on off-line simulated data. Results of the comparison between the least error squares technique and the new proposed algorithm are reported in this paper.

Apparatus for maintaining the frequency of an oscillator within a predetermined frequency range

Abstract: The frequency of a local oscillator is maintained within a small frequency window around any one of a number of reference frequencies so that it can lock onto the frequency of an incoming color burst (CHRM). The oscillator (10) may be a current-controlled oscillator. Its control input is switched via a fet (32) to a capacitor (20) charged to a voltage level which will, when connected to the oscillator control input, result in the correct oscillator frequency (Fo). The connection to this capacitor (20) is made when the charge on either one of two control capacitors (22,24) exceeds a threshold value. The threshold values are exceeded when the local oscillator frequency (Fo) is respectively greater than or less than the reference frequency (Fr) by a predetermined frequency difference.

Baseband processing frequency-drift-compensation for QDPSK signal transmission

Abstract: BER performance of differential detection severely degrades with carrier frequency drift. This Letter proposes a baseband processing frequency-drift-compensation (FDC) scheme that estimates the phase rotation of the differential detector output expressed in complex form and multiplies the complex conjugate of the estimate to cancel the phase rotation. 16 Kbit/s QDPSK transmission experiments using a simulated Rayleigh fading channel show that a carrier frequency drift of up to about 3/64 times the bit rate can be tolerated with the use of the proposed baseband FDC

Numerical investigation of a three-mirror resonator for a TE CO(2) laser.

Abstract: A numerical model of a three-mirror resonator for a TE CO2 laser was developed. This model was used to determine if a three-mirror resonator with an etalon could be used to ensure tunable single-mode action on the lower gain lines of CO2. Single-mode pulse energies were also predicted and good agreement was found with experimentally measured values. An analysis of the thermal frequency drift of the resonator is also presented.

Error amplifier for multiple frequency oscillator control

Abstract: A multiple frequency scan oscillator control system includes a phase locked loop operative upon a scan oscillator to provide phase and frequency synchronization thereof to a periodic reference signal. A static phase error correction is operative to provide adjustment of the free-running or static frequency of the scan oscillator. An error amplifier includes a pair of intercoupled differential amplifier configurations one having a constant current source and the other having a frequency dependent current source which responds to a frequency dependent bias current to alter amplifier gain. A threshold detection circuit includes a differential amplifier pair coupled to a pair of switching circuits for establishing a threshold action in response to system error voltage to indicate large magnitude error voltages and signal the need for free-running frequency adjustment of the oscillator.

FM modulator for compensating modulation characteristics on each channel

Abstract: A frequency-modulation modulator in a cellular wireless telephone for modulating frequency after uniformly and linearly compensating for frequency characteristics to be suitable for each engaged channel in a cellular wireless telephone. Since frequency modulation characteristics are compensated uniformly and linearly according to each one of a plurality of channels, an error due to the frequency distorted modulation can be prevented and the cellular wireless telephone becomes more reliable. The frequency-modulation modulator includes a controller for providing data to assign the channel by sensing a transmitting/receiving channel, and for generating a switch control signal corresponding to each channel, and of a frequency compensator for compensating for frequency characteristics according to each channel by regulating a gain of an input channel by means of the switch control signal from the controller, and of a capacitance converter for converting a given voltage value from the frequency compensator into a capacitance value, and of a resonator for generating a given resonance frequency with the capacitance value of the capacitance converter, and of a voltage controlled oscillator for generating an oscillation frequency to modulate the corresponding frequency based on the resonance frequency.

Crystal oscillator having frequency adjustment responsive to power supply voltage

Abstract: Frequency compensation for a crystal oscillator circuit whose oscillation frequency is dependent on source voltage applied thereto. When a capacitor is added to the frequency compensation terminal of the crystal oscillator circuit, the circuit changes the oscillation frequency thereof on the basis of the capacitance of the capacitor. A source voltage detector compares the source voltage being applied to the crystal oscillator circuit with a predetermined reference voltage and produces a control signal matching whether the source voltage is higher or lower than the reference voltage. On receiving the control signal, a control switch turns on or off the contact thereof to add or not to add the capacitor to the frequency compensation terminal. Assuming that the characteristic of the crystal oscillator circuit is such that the oscillating frequency decreases with the decrease in the source voltage, when the source voltage is low, the capacitor for frequency compensation is not added so as to increase the oscillation frequency of the crystal oscillator. Conversely, when the characteristic is such that the oscillation frequency increases with the decrease in the source voltage, the capacitor is added so as to decrease the oscillation frequency.

Phase locked loop with d.c. modulation

Abstract: A D.C. modulated phase locked oscillator (60, 80, 100, 140, 160, 190, 220, 264, or 290) includes a phase locking oscillator (70, 90, 128, 180, 192, 222, 266, or 292) and a D.C. modulator (72, 92, 130, 156, 182, 194, 224, 268, or 294). Both a forward path (14) and a feedback path (16) are D.C. modulated. D.C. modulation of the feedback path (16) optionally includes changing the frequency in the feedback path (16) as a function of the frequency of a modulation oscillator (64), changing the frequency in the feedback path (16) by a plurality of pulses for each cycle of the modulation oscillator (64), removing pulses from the feedback path (16), adding pulses to the feedback path (16), dividing the frequency in the feedback path (16) by higher and lower dividing ratios, preventing one cycle in the feedback path (16) from developing a ''high'' in the feedback path (16), holding a ''high'' in the feedback path (16) between two adjacent pulses, mixing quadrature frequencies with the feedback frequency in the feedback path (16), changing one input to a variable modulus divider (48) by means of a parallel adder (272), and using logic elements (148) to remove pulses from the feedback path (16).

Optical laser frequency stabilizer

Abstract: An optical laser frequency stabilizer which is simple, inexpensive, produces an unmodulated output, and a highly controlled oscillation frequency, wherein signals supplied to a master laser are modulated with a signal which is switched between four or more different levels to control the oscillation frequency of the master laser to the frequency of an absorption line; and wherein the beat frequency of signals from the master laser and a slave laser is counted by an up-down frequency counter in synchronism with the modulation signal and, in response to the obtained total count, the oscillation frequency of the slave laser is controlled to a frequency based on the center frequency of the oscillation of the master laser so that an unmodulated output is generated which is not affected by variations in the powers of the laser beams. The laser frequency can be offset from the frequency of the absorption line, and also the offset frequency can be varied continuously.