Rockwell International Corporation

Other

United States of America As Represented by the Secretary of the Air Force

Marvin E Frerking

Roy W Berquist

Glenn R Hykes

A means is provided to establish oscillations on a particular mode or resonance of a quartz crystal in a crystal oscillator and to discriminate against other modes. This is done by injecting a signal close in frequency to the desired mode until oscillation have been established and saturation of the active element has occurred. The limiting process then discriminates against the unwanted modes and holds the oscillation on the desired mode.

Injection mode steering oscillator

A means is provided to estimate the amount of frequency deviation experienced in a precision resonator resulting from the effects of previous thermal history, acceleration, or aging by determining the differential effect of the perturbing condition on different resonant modes in the same resonator or on different resonators exposed to the same environment. The measurements may be made simultaneously, or sequentially against an independent frequency source. Residual frequency hysteresis effects may be determined in connection with an independent temperature sensor if the exact temperature in not known.

Residual frequency effects compensation

A digital mixer employs a plurality of flip-flops to mix two digital input signals and provide a beat frequency output. The first input signal is provided as a clock signal to a first D flip-flop and to a third JK flip-flop. The second input signal is provided as a clock signal to a second D flip-flop. The inverted output of the first flip-flop is provided as a clock input to a fourth JK flip-flop. The non-inverted and inverted outputs of the second flip-flop are connected, respectively, to the J and K inputs of the third flip-flop. The non-inverted outputs of the second and third flip-flops are input to a first AND gate, the output of which connects to the J input of the fourth flip-flop. Likewise, the inverted outputs of the second and third flip-flops are input to a second AND gate, the output of which connects to the K input of the fourth flip-flop. The non-inverted output of the fourth flip-flop provides a beat frequency that is one-half the difference frequency of the two input signals. The third flip-flop in the digital mixer prevents glitches around the transition time of the beat frequency output even for very low beat frequencies.

Deglitched digital mixer circuit

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.

Integrator controlled time compensated clock oscillator

In order to compensate for mechanical vibration that corrupts the RF output spectrum of a crystal oscillator, three accelerometers are mounted with the oscillator and aligned on mutually perpendicular axes. The outputs of the accelerometers are digitized and applied to adaptive transversal filters comprising a digital signal processor. The crystal oscillator is placed on a vibration table and its output is compared with an external frequency reference. The tap weights of the filters are then optimized so that the vibration components of the output spectrum of the oscillator are minimized. After the tap weights of the filters are determined and fixed, the filters provide vibration compensation for the oscillator. During operation of the crystal oscillator, the outputs of the filters are summed and applied to a varactor in the oscillator to compensate the output for the effects of mechanical vibration.

Vibration compensated crystal oscillator

A closed loop frequency source includes a controllable oscillator that provides a first frequency source, a reference oscillator that provides a second signal, and a comparator that compares the two frequencies to provide an error signal that represents the difference between the frequencies. The error signal is used by an error signal generator to generate a compensation signal which offsets the carrier frequency that drives an output device such as a time-of-day clock so that the output device automatically gains or loses the previously accumulated time error without the necessity of being periodically updated.

Closed loop temperature compensated frequency reference

The frequency of an electronic oscillator is controlled by a crystal located in the oven. The heaters in the oven include resistance elements for quick warm-up, and steady state. The circuit allows the quick warm-up power to be reduced incrementally as the set temperature is approached and effects a smooth transition to the steady-state heater. This is accomplished by circuit features which reduce the control loop gain when high power is applied to the heaters and increase the gain as the warm-up power decreases.

Variable gain oven temperature control circuit

Temperature stability is quickly achieved for a crystal oscillator mounted in a warm-up crystal oven because the heat is applied proportionally to the mass of the oscillator and circuitry during the initial warm-up period of time and then applied proportionally to the area that will allow compensation for thermal loss after the warm-up period. The oscillator crystal is encapsulated within a case along with an oscillator circuit for the oscillator crystal that is thermally mounted to the case. A controlled heater heats the warm-up crystal oven and crystal oscillator. The controlled heater is controlled by a temperature controller that responds to a first thermal sensor that senses the temperature of the case and a second thermal sensor that senses the temperature of the controlled heater.

Accelerated warm-up crystal oven

A time compensated clock oscillator is disclosed that has a first low power oscillator that drives an output device such as a time-of-day clock, a second more precise oscillator whose output is compared to the output of the first oscillator, and develops a correction signal that is used to periodically correct the output device.

Time compensated clock oscillator

An oscillator is temperature compensated by adjusting a slave oscillator with an error signal, that is produced by using the temperature of a reference oscillator to determine the frequency error of the reference oscillator, and then adjusting the frequency of the slave oscillator until its frequency coincides with an ambient reference frequency.

Non-linear digital-to-analog conversion is performed by employing a plurality of counting rates and counting intervals in a digital counter to generate a variable width pulse, the width of which determines the desired analog value corresponding to the digital value to be converted.

Non-linear digital-to analog conversion

Noise suppression in a radio receiver is accomplished by clamping the receiver detector output for a predetermined period each time the noise content in the receiver signal exceeds some predetermined threshold value.

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Cedar Rapids, IA, United States of America

Marvin E Frerking