Oscillators – Automatic frequency stabilization using a phase or frequency... – Particular error voltage control
Reexamination Certificate
1999-07-15
2002-07-09
Mis, David (Department: 2817)
Oscillators
Automatic frequency stabilization using a phase or frequency...
Particular error voltage control
C331S00100A, C331S016000, C331S023000, C331S025000, C327S156000, C327S159000
Reexamination Certificate
active
06417738
ABSTRACT:
STATEMENT RE FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
REFERENCE TO A “MICROFICHE INDEX”
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to adaptive frequency-hopping oscillators and phase-locked oscillators. More particularly, the present invention pertains to phase-locked oscillators with adaptive circuitry, to lead-compensated digital integrators for use in phase-locked oscillator, and to nonlinear D/A converters for use in learning systems such as adaptive frequency-hopping oscillators.
2. Description of the Related Art
Frequency-hopping transmitters are capable of transmitting radio frequencies on successive ones of a plurality of individual output frequencies with the output frequencies chosen in accordance with a code for a particular day or period.
Since the transmitted information remains on a given frequency for a matter of seconds, or microseconds, and since the order of selection of frequencies can be changed rapidly and precisely, information can be successfully encoded by the use of frequency-hopping transmitters.
As an example, when used to transmit video signals, a frequency-hopping transmitter could transmit each successive scan line at a different frequency.
The individual output frequencies are called channels, and the process of dividing a range of frequencies into channels is called channelizing. Each channelized frequency is produced by applying a selective voltage to a voltage controlled oscillator, and the selective voltages that will drive the voltage controlled oscillator to the channelized frequencies are called channelizing voltages.
Frequency-hopping oscillators can be designed to learn channelizing voltages for a particular voltage controlled oscillator, to correct for errors of proportionality and nonlinearity of analog components, and to correct for temperature-caused drift of analog components. Learning systems are sometimes called adaptive systems or adaptive learning systems.
Charavit et al., in U.S. Pat. No. 4,511,858, issued Apr. 16, 1985, teaches embodiments of phase-locked oscillators that use analog integrators. Their phase-locked oscillators are adaptive in that channelizing voltages are stored, recalled, corrected through a phase-locked loop, and placed again in storage.
A frequency-hopping transmitter is a transmitter that utilizes a frequency-hopping oscillator. In like manner, a frequency-hopping receiver is a receiver that utilizes a frequency-hopping oscillator. A frequency-hopping oscillator is a phase-locked oscillator that is channelized and whose channelized frequencies can be accessed rapidly in response to a predetermined program.
Phase-locked oscillators are used in transmitters for producing an output frequency that is crystal referenced, for demodulating frequency modulated signals in radio receivers, to achieve frequency deviation compression in frequency-modulated and phase-modulated receivers, and in various devices in which both rapid change to selected frequencies and precise frequency control are critical.
The use of phase-locked oscillators to achieve frequency deviation compression in radio receivers is taught by Lautzenhiser in U.S. Pat. No. 5,091,706, issued Feb. 25, 1992; in U.S. Pat. No. 5,497,509, issued Mar. 5, 1996; and in U.S. Pat. No. 5,802,462, issued Sep. 1, 1998.
Phase-locked oscillators can be AC modulated, DC modulated, or both, as taught by Lautzenhiser in U.S. Pat. No. 5,091,706; in U.S. Pat. No. 5,097,230, issued Mar. 17, 1992; and in U.S. Pat. No. 5,311,152, issued May 10, 1994. In addition, phase-locked oscillators can be channelized as also taught by the aforesaid Lautzenhiser patents. Frequency-hopping oscillators may be AC and/or DC modulated using principles taught in the aforesaid Lautzenhiser patents.
A phase-locked oscillator includes both a forward path and a feedback path. As defined herein, the forward path extends from a comparing device, or phase detector, through a VCO, to an output frequency conductor. The feedback path extends from the output frequency conductor, through one or more frequency dividers which serve as channelizing devices and/or other devices in the feedback path, to the comparing device. In accordance with these definitions, the comparing device is not a part of either path.
In phase-locking oscillators, both the forward path and the feedback path are connected to a crystal-controlled reference oscillator by a comparing device. Phase lock is achieved when a feedback frequency from a voltage controlled oscillator equals the frequency of the reference oscillator.
Channelization of phase-locking oscillators is achieved by channelizing the feedback path. The feedback path is channelized by dividing frequencies in the feedback path by N, as shown herein, by any of the ways taught by Lautzenhiser in the aforesaid patents, by partial N manipulation, or by nearly any other method that is conceivable.
Since channelization of the feedback path is dependent only upon the time required to divide the frequency in the feedback path by a different number, if a channelization voltage is simultaneously applied to the VCO, channelization is extremely rapid.
AC modulation of the forward path, at frequencies above the loop frequency, may be achieved by applying an analog voltage, or modulating voltage, to the VCO via a modulation resistor, as taught in the aforesaid Lautzenhiser patents, or by any other suitable means.
DC modulation of the feedback path may be achieved by digital manipulation of pulses in the feedback path, as taught by Lautzenhiser in the aforesaid patents, or by any other suitable means.
In phase-locked oscillators, an error signal is produced by a difference in a feedback frequency to a reference frequency. This error signal may be integrated by analog or digital circuitry.
In phase-locked oscillators that use an analog integrator, the error signal is time-integrated. This time-integrated error signal, which is a voltage, is applied to the VCO during the integration process. The error signal disappears and integration stops when phase lock is achieved.
In phase-locked oscillators that use a digital integrator, the error signal is integrated by summing clock-timed UP and DOWN error signals. D/A conversion changes the digitally-integrated error signals into voltage which is applied to the VCO during the integration process. Error signals disappear and integration stops when phase lock is achieved.
BRIEF SUMMARY OF THE INVENTION
The frequency-hopping oscillators of the present invention include adaptive circuitry with learning and recalling functions, thereby providing frequency-hopping oscillators in which an output frequency of a VCO can be channelized without waiting for phase locking.
Channelizing information, and/or frequency-correction information, is developed and stored that, when recalled will drive the output frequency to the desired channel almost instantly, and with very little deviation from frequencies that would phase lock for the respective channels.
The channelizing information compensates for errors in proportionality and linearity of such components as a D/A converter, an analog combiner/offsetter, resistor values, and/or a VCO. Subsequent return to the same channelized frequency results in automatic correction for temperature drift of various components that may have occurred since the channel was last accessed.
That is, adaptive circuitry stores channelizing information that can be recalled and converted into a plurality of channelization voltages, one for each channel. Thereafter, the output frequency of the VCO can be driven to channelized frequencies that approach phase lock without waiting for the phase-locked oscillator to phase lock.
The various embodiments include digital integrators and special circuitry that mimics analog circuitry. That is, they each include circuity that provides digital lead compensation, thereby providing loop stability for the digital integrators, even as analog integrators use a lead resistor in series with an integrating capacitor to ach
Emhiser Research Limited
Miller Wendell E.
Mis David
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