Showing papers on "Frequency drift published in 1981"

Method and assembly for monitoring respiration and detecting apnea

Abstract: A method and assembly for monitoring respiration and detecting apnea. The assembly includes an oscillator for generating an electromagnetic field having an output frequency in the radio frequency range and a high Q passively tuned LC circuit which has a resonant frequency variable in the radio frequency range generated by the oscillator. The LC circuit responds to the electromagnetic field by absorbing electromagnetic energy from the field when the resonant frequency matches the output frequency of the oscillator. A band is positioned about the subject's chest or abdominal cavity to vary the resonant frequency of the LC circuit in response to the expansion and contraction of the subject's chest or abdominal cavity. A detecting means is also provided for detecting when the LC circuit is responsive to the electromagnetic field established by the oscillator. In one embodiment the output frequency of the electromagnetic field established by the oscillator is maintained constant and the detecting means includes reset timing means for providing a signal when the LC circuit fails to respond to the electromagnetic field within a predetermined time period. In a second embodiment the output frequency of the electromagnetic field established by the oscillator is varied within the predetermined frequency range and the detecting means includes reset timing means for providing a signal when the LC circuit fails to respond to the electromagnetic field at different resonant frequencies within the predetermined frequency range within a predetermined time period.

A voltage-controlled switched-capacitor relaxation oscillator

Abstract: A new switched-capacitor (SC) oscillator is described. The oscillator is easily modified to be either voltage controlled or digitally programmed. Although the oscillator is practical only when its oscillating frequency is less than about 1/25 the clock frequency (because of the excess phase jitter that develops at higher ratios), it is useful in a number of low frequency applications, especially when stability is important.

Optical FSK heterodyne detection experiments using semiconductor laser transmitter and local oscillator

Abstract: Frequency modulated semiconductor laser signals are demodulated by optical heterodyne detection using an independently temperature stabilized semiconductor laser local oscillator and a square-law detector followed by electrical frequency discrimination circuitry. Short-term and long-term beat frequency stability of the free-running laser transmitter and the local oscillator are delineated. Direct frequency modulation characteristics of the laser transmitter are studied by observing the intermediate frequency spectra. Frequency modulation-demodulation of pulse pattern signals at 100-200 Mbit/s is demonstrated. Reduction of the intermediate frequency fluctuation to less than 5 MHz is realized by employing a feedback of the RF frequency discriminator output to the local oscillator injection current.

Battery saving frequency synthesizer arrangement

Abstract: The phase-locked loop section (10, 14) of the synthesizer is periodically disconnected from the battery supplied power by means of a switch (60). In order to prevent substantial drift of the phase-locked loop during such power interruption, means (22, 24) are provided for maintaining a control signal on the VCO (12) associated with the loop (10) that maintains the VCO frequency. By minimizing the frequency drift, the loop can be re-locked in a short period of time following each power interruption.

Modulation frequency characteristics of directly optical frequency modulated AlGaAs semiconductor laser

Abstract: Optical frequency spectra of directly frequency modulated AlGaAs semiconductor laser in the 0?5.2 GHz range were measured by using a Fabry-Perot interferometer and a birefringent optical filter. The frequency deviation is linearly proportional to the RF modulation current. The measured modulation frequency characteristics for the frequency deviation show that the thermal effect is predominant in the frequency below 10 MHz. It has a resonance peak which behaves just like the peak observed in the modulation. Experimental results agreed well with theoretical values calculated by considering thermal effect and carrier-dependent refractive index variation.

Television tuning system with electronic frequency adjustment apparatus

Abstract: A television (TV) receiver tuning system for selecting one of a plurality of receivable TV channels comprises a frequency selective radio frequency device including trimming elements for receiving TV signals, a local oscillator controlled by a first control signal and a mixer in which the TV signals and the local oscillator signal are heterodyned to develop an intermediate frequency signal A first control device develops the first control signal in response to the selection of a TV channel to control the local oscillator frequency so that the mixer shifts the selected TV channel signal to the IF frequency A second control device including a PROM trims the frequency selectivity of the RF device using its trimming elements unaffected by selection of the TV channel whereby mechanical alignment of the TV tuning system can be avoided In other aspects of the invention, the second control device develops signals for adjusting tunable circuits in the IF amplifier, for adjusting the tracking of the local oscillator frequency in relation to its control signal, and, in a double-conversion tuner, for adjusting the frequency of a second local oscillator

A bipolar voltage-controlled tunable filter

Abstract: A complete monolithic state variable filter is described which has been fabricated with bipolar technology. Two-quadrant multipliers are used in a novel fashion to achieve integration time constant large enough for audio purposes. Voltage control of frequency response from 20 Hz to above 20 kHz has been achieved without sacrifice of accuracy (notch depth >50 dB, low-pass and bandpass responses accurate to better than 0.1 dB), dynamic range (>90 dB), power supply rejection (PSRR>40 dB) or frequency drift (<200 ppm//spl deg/C). The design has been shown to be generally useful in the design of self-contained bipolar filters.

Digital frequency/phase locked loop

Abstract: A frequency/phase locked loop for providing signals which are frequency and phase locked to signals at a reference frequency from a reference oscillator which is determinative of the frequency stability includes a frequency-controlled generator of a lower frequency stability. The frequency controlled generator is responsive to control signals for switching between first and second frequencies which are substantially higher than the reference frequency. The second frequency is approximately one to ten percent higher than the first frequency. The frequency divider coupled to the frequency generator provides an output signal at the same frequency as the reference oscillator. A digital phase comparator compares the outputs of the frequency divider with the reference signals. A digital integrating stage coupled to the comparator provides the control signals such that during a first portion of a period of the reference signals the first frequency is selected and during a second portion of the period the second frequency is selected.

Multifrequency piezoelectric horn system

Abstract: A multifrequency piezoelectric sound-generating system is provided with a piezoelectric vibrator for generating audible sound at two or more resonance frequencies, an oscillator circuit connected to the piezoelectric vibrator for oscillating at one of the resonance frequencies, and a modulator circuit connected to the oscillator circuit for amplitude-modulating the oscillator circuit with a modulating frequency substantially equal or close to a frequency separation between the resonance frequencies to energize the piezoelectric vibrator with frequency-modulated waves to generate multifrequency audible sound. The modulator circuit may have a frequency divider that is operative in response to an oscillating frequency in the oscillator circuit for dividing or counting down the oscillating frequency into the modulating frequency to modulate the oscillator circuit therewith. The piezoelectric vibrator may include a diaphragm, a generally rectangular metal sheet which is smaller in size than the diaphragm and mounted on the diaphragm, and a sheet of a piezoelectric material mounted on the metal sheet.

Transmission systems for transmitting signals over power distribution networks, and transmitters for use therein

Abstract: A transmission system, for transmitting signals over an electrical power distribution circuit, comprises a transmitter arranged to produce at least two carrier signals of different frequency and to modulate each of them with the same digital signal. The respective frequencies of the carrier signals are derived by frequency division from a common master oscillator, and are thus phase-coherent. The system includes a receiver for receiving the signals, comprising a respective input circuit for each modulated carrier, the input circuits each being tuned to the frequency of their respective carrier signal. A plurality of oscillator signals of different frequencies, derived from a variable frequency oscillator, are used to beat the received carrier signals to respective signals at a common frequency, which signals are summed. The summed signal at the common frequency is applied to one input of a phase detector, whose other input is connected to receive another oscillator signal, also at the common frequency, from the variable frequency oscillator. The output signal from the phase detector is applied to the variable frequency oscillator to lock its frequency to those of all the carriers and therefore to that of the master oscillator in the transmitter. The digital signal is derived from the output of the phase detector by digital correlation techniques.

Achievement of 1 MHz frequency stability of semiconductor lasers by double-loop AFC scheme

Abstract: A temperature-controlling AFC system has been developed to realise high-frequency stability with semiconductor lasers. The frequency drift in DC operation can be reduced to below 1 MHz peak-to-peak. When necessary, the laser frequency can be modulated directly in the AFC state while the centre frequency is kept stabilised within 3 MHz. A heterodyne experiment was also performed using two frequency stabilised lasers; a stable IF output could be obtained for 10 min.

Wideband, synthesizer switched element voltage controlled oscillator

Abstract: An exceptionally wideband, synthesizer controlled voltage controlled oscillator is disclosed which is characterized by a plurality of pin diode frequency shift networks which, when actuated shifts the frequency of the oscillator in selectable binary steps within a wide frequency range in the order of 48 MHz. Special means are included to prevent undesireable parasitic oscillation modes when such frequency shift networks are in an inactuated, switched off mode. A multiple varactor tuning circuit is provided for selecting a precise frequency within a relatively narrow frequency band on the order of 6 MHz.

Radio receiver having phase locked loop and automatic frequency control loop for stably maintaining local oscillator frequency of voltage-controlled local oscillator

Abstract: A radio receiver comprises a phase locked loop and an automatic frequency control loop which are selectively coupled with a voltage-controlled local oscillator to control a local oscillator frequency. The phase locked loop and the automatic frequency control loop have a common loop filter which supplies the voltage-controlled oscillator with a control voltage. The loop filter is arranged so that its time constant may be switched from a small value to a great value in response to switching of the operation mode of the voltage-controlled oscillator from a phase locked loop control mode for the selection of broadcasting station to an automatic frequency control loop control mode for the maintenance of the local oscillator frequency after tuning of the radio receiver. The radio receiver can be arranged so that the local oscillator frequency may be maintained by the phase locked loop after the tuning of the receiver to a weak broadcast signal when muting control is rendered ineffective by a muting switch.

Apparatus for measuring the oscillation frequency of a voltage controlled oscillator

Abstract: The apparatus of the present invention is provided with a reference oscillator having an oscillation frequency lower than the oscillation frequency of a voltage controlled oscillator to be measured. Either reference oscillator or the oscillator to be measured is controlled by a phase lock loop so that a difference between a frequency N times the oscillation frequency of the reference oscillator and the oscillation frequency of the voltage controlled oscillator may assume a predetermined value. A coarse oscillation frequency of the voltage controlled oscillator is obtained from its control voltage. The oscillation frequency of the reference oscillator is counted by a counter and the coarse frequency is divided by the count value and then an integer value is obtained by rounding off the divided result. The count value of the counter is multiplied by the divided result to obtain a highly accurate oscillation frequency value for the voltage controlled oscillator with high accuracy.

Phase-locked loop frequency demodulator and frequency synthesizer

Abstract: A combined phase-locked loop frequency demodulator and frequency synthesizer for frequency-modulated wave receivers using two phase-locked loops respectively for synthesis and for demodulation In this device, the frequency-modulated signal is applied to one of the inputs of a first phase comparator whose other input is coupled to the output of a voltage-controlled oscillator, which output is also coupled, through a prescaler and a programmable frequency divider mounted in cascade, to one of the inputs of a second phase and frequency comparator whose other input is coupled to the output of a crystal-controlled reference oscillator The output of the first comparator is coupled by means of a first low-pass or bandpass filter to a first input of an analog adder whose second input is coupled by means of a second low-pass filter, having a relatively low upper cut-off frequency, to the output of the second comparator The output of the adder which combines the signals from the two filters is connected to the frequency-control input of the voltage-controlled oscillator The output of the first filter supplies the demodulated signal and thus constitutes the output of the frequency demodulator, whose phase-locked loop is combined with the phase-locked loop of the frequency synthesizer, which selects the frequency of the modulated carrier wave, by means of the adder and the single voltage-controlled oscillator which are the common elements of both phase-locked loops

Frequency Stabilization Of Semiconductor Lasers

Abstract: Heterodyne-type optical communication will provide a wide bandwidth and a high signal-to-noise ratio. However, at present the frequency drift of semiconductor lasers is the greatest difficulty, which must be overcome before the heterodyne-type communication is realized. This paper describes an automatic frequency control system for GaAkAs semiconductor lasers. The frequency drift can be reduced to below 10 MHz. Besides, without sacri ficing the frequency stability, a tunable frequency range of 0.5 THz is obtained. These values are good enough for heterodyne-type optical communication systems.

Frequency control system for radio apparatus employing filter amplifier operated at harmonic of frequency of synthesized signal source

Abstract: An improved frequency control system for radio apparatus is provided, which is especially advantageous for employment in portable, battery powered, multichannel, radio transceivers.The system involves both individual and combinational type improvements relating to the constructional and operational aspects of transceiver equipment. Some salient features of the system include digital frequency synthesizer circuitry having a frequency and phase locked loop employing a voltage controlled oscillator, out-of-band selection detecting and transmit inhibit signal generating circuitry, and filtering and amplifying circuitry employing voltage controlled tuning and improved wide-band inter-stage coupling for supplying frequency controlling signals for both a receiver and a transmitter from a common excitation source.

Monolithic voltage controlled oscillator

Abstract: A monolithic voltage controlled oscillator is fabricated on a single semiconductor body. The oscillator includes an FET and a varactor diode interconnected such that a voltage applied across the varactor modulates the oscillating frequency of the FET output.

Local oscillator frequency drift compensation circuit

Abstract: The invention provides a double superheterodyne receiver having the usual first and second frequency changers associated with first and second local oscillators. The second local oscillator is provided as a voltage controlled oscillator and means are provided for determining the difference frequency between the two local oscillators to produce a control signal which is applied to the second local oscillator to tend to maintain the difference frequency constant.

Frequency and phase controlled HF oscillator - uses frequency divider and phase comparator receiving quartz oscillator reference frequency

Abstract: The high frequency oscillator has a frequency divider (4) with a variable division ratio, supplying a fraction of the oscillator output frequency to a phase comparator (2) for comparison with a reference frequency (Fr). The output of the phase comparator (2) is used to provide a control voltage for frequency regulation of the oscillator. The division ratio of the frequency divider (4) and the momentary value of the control voltage provided by the phase comparator (2) are held and then again released via a control circuit (11), responsive to the two inputs to the comparator (2) being in phase. Pref. the division ratio of the frequency divider (4) is selected by a digital input device (5) which it operates as a counter.

Zone switching system for a frequency synthesized transceiver

Abstract: A frequency synthesized transceiver capable of tuning to a plurality of communication channels is disclosed. The transceiver includes a receiver section and a transmitter section which are coupled to the synthesizer which generates the appropriate injection signals to achieve tuning. The frequency synthesizer includes a multiposition switch which accesses various addressable memory locations in a programmable read-only memory where the appropriate divisors are stored to cause tuning of the synthesizer to the appropriate communication channel. A zone selector switch enables grouping and easy retrievability of channels. The divisors are supplied to a single synchronous binary swallow counter which works in conjunction with a dual modulus prescaler to monitor the frequency output of the voltage controlled oscillator. A programmable divider coupled to a reference oscillator source is compared with the output of the synchronous counter in a digital and analog phase detector. The phase detector supplies signals through a loop filter to apply the appropriate voltage to the voltage controlled oscillator. The phase detector includes means to rapid advance the voltage controlled oscillator to cause frequency tuning.

Low-noise digitally tunable phase-locked loop frequency generator

Abstract: A variable-frequency main oscillator of digitally tunable high output frequency f A is controlled by the integrated output voltage of a phase discriminator receiving on the one hand a relatively low comparison frequency and on the other hand a matching feedback frequency stepped down from output frequency f A by frequency division or by heterodyning with an auxiliary frequency f H of the same order of magnitude from an ancillary oscillator, a difference frequency f D =f A -f H is fed to a frequency discriminator delivering a corrective voltage, independent of that emitted by the phase discriminator through a filter network, to the control input of the main oscillator. A pair of frequency selectors varying the feedback frequency and/or the comparison frequency enable the output frequency f A to be adjusted in coarse and fine tuning steps, the coarse adjustments being also applied to the auxiliary frequency f H to limit the excursions of the difference frequency f D . In order to minimize shifts in the corrective voltage due to changes in the setting of the fine-tuning selector, a digital command generated by that selector is converted into an analog compensating voltage subtracted from the output voltage of the frequency discriminator.

Temperature compensated crystal oscillator

Abstract: A frequency regulated crystal oscillator with (1) an oscillating circuit made up of an amplifier, piezoelectric crystal and voltage controls capacitor, and (2) a two-part compensating circuit connected to the terminals of the variable capacitor, each part having thermistors whose resistance varies with temperature to produce complementary signals and which are shunted with electrical resistors.

Method and circuitry for chirped oscillator automatic frequency control

Abstract: The starting frequency and sweep rate of a chirped frequency-shift-keyed oscillator are automatically controlled for correction of long-term drift. The substantially linear swept frequency output of the oscillator, during each of a successive multiplicity of swept frequency chirps, is counted and the count converted to an error signal utilized to control an appropriate potential in the oscillator circuit. The initial frequency is monitored, where the swept frequency range is small compared to the initial frequency, by counting the number of cyles during a chirp period in obtaining a first error signal from the total cycle count. The frequency-chirp ramp rate is monitored by counting the number of cycles during an initial portion, e.g. the first one-tenth, of the chirp interval, and comparing the count thus obtained with a frequency count obtained during an identical-length interval at the end of the frequency chirp; the count difference is utilized for automatic correction of change in frequency chirp sweep rate. Circuitry for implementation of initial frequency and/or sweep rate automatic correction is described.

Low temperature coefficient wide band-width voltage controlled oscillator

Abstract: An emitter coupled oscillator having a wide bandwidth capability is tuned by an applied voltage or current. The oscillator obtains its feedback coupling by means of a differential amplifier which greatly reduces the second order temperature versus frequency drift. This is accomplished by forcing the oscillator to trip under conditions which greatly reduce V BE in the switching transistors.

Range control circuit for counter to be used in a frequency synthesizer

Abstract: A frequency synthesized transceiver capable of tuning to a plurality of communication channels is disclosed. The transceiver includes a receiver section and a transmitter section which are coupled to the synthesizer which generates the appropriate injection signals to achieve tuning. The frequency synthesizer includes a multiposition switch which accesses various addressable memory locations in a programmable read-only memory where the appropriate divisors are stored to cause tuning of the synthesizer to the appropriate communication channel. A zone selector switch enables grouping and easy retrievability of channels. The divisors are supplied to a single synchronous binary swallow counter which works in conjunction with a dual modulus prescaler to monitor the frequency output of the voltage controlled oscillator. A programmable divider coupled to a reference oscillator source is compared with the output of the synchronous counter in a digital and analog phase detector. The phase detector supplies signals through a loop filter to apply the appropriate voltage to the voltage controlled oscillator. The phase detector includes means to rapid advance the voltage controlled oscillator to cause frequency tuning.

Color synchronizing circuit

Abstract: A color synchronizing circuit comprises a phase locked loop which includes a voltage controlled oscillator including a ceramic vibrator. Phase comparison is made of an intermittent color burst and the output of the voltage controlled oscillator and the phase comparison output is applied to a low pass filter. The low pass filter provides a control voltage associated with the phase difference of these two signals to the voltage controlled oscillator. The frequency variable range Δf of the voltage controlled oscillator is selected such that a relation Δf<±f H is met with respect to the repetition frequency f H of the color burst. The low pass filter comprises a dual time constant circuit, which sufficiently attenuates a beat signal from the phase comparator, thereby to make narrow the pull-in range of the phase locked loop. On the other hand, a sawtooth waveform voltage of a stepwise fall is obtained from a sweeper circuit and is applied to the voltage controlled oscillator together with the output voltage from the low pass filter as a control voltage.

Broadband injection locked oscillator system

Abstract: The broadband injection locked oscillator system comprises a first voltage controlled oscillator having a signal output for a first signal controlled to have a first frequency in a first relatively broad frequency range, and a second voltage controlled oscillator having a signal output for a second signal controlled to have a second frequency in a second relatively broad frequency band. The output of the second oscillator is coupled to a signal input of the first oscillator to injection lock the first oscillator to the second oscillator. The second frequency is harmonically related to the first frequency when the injection lock occurs.

An Electrostatic Voltage Sensor Using Surface Acoustic Waves

Abstract: A compact electrostatic voltage sensor has been developed using a delay line type SAW oscillator. An additional collecting electrode is settled on a surface of a piezoelectric substrate between input and output interdigital transducers. The electrostatic voltage applied to the collecting electrode is detected by a frequency change of the SAW oscillator. Piezoelectric ceramics with d=-42×10-12C/N are used for making the SAW oscillator. The sensitivity achieved is 0.64 Hz/V at oscillation frequency of 23 MHz.