Coded data generation or conversion – Analog to or from digital conversion – Digital to analog conversion
Reexamination Certificate
2000-03-31
2002-06-25
JeanPierre, Peguy (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Digital to analog conversion
C341S145000, C341S154000
Reexamination Certificate
active
06411237
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 digital-to-analog (D/A) converters. More particularly, the present invention relates to D/A converters taught herein that eliminate holes in output voltages by intentionally-placed downward steps in output voltages, thereby producing nonlinear output voltages. nonlinear digital-to-analog (D/A) converters for use in phase-locked oscillators, and in learning systems such as adaptive frequency-hopping oscillators.
2. Description of the Related Art
Digital-to-analog converters have found various uses in electronic devices. One use that has gained importance is D/A conversion of digitally-stored channelizing information to analog channelizing voltages used in frequency-hopping oscillators.
In frequency-hopping oscillators, it is sometimes advantageous to store channelizing information in digital form for a plurality of channelized frequencies, to subsequently recall digitally-stored channelizing information for one of the channelized frequencies, to D/A convert the recalled digital information for that one channel into a channelizing voltage, and to drive an output of frequency of a voltage controlled oscillator (VCO) approximately to phase lock for that one channelized frequency in response to that channelizing voltage.
Clark et al., U.S. Pat. No. 5,703,587, issued Dec. 30, 1997, use three 6-bit D/A converters and decoding logic, such as first and second exclusive OR gates, to convert sixteen bits of digital information.
Their D/A converter produces dual addresses by making the binary weight of the most significant bit of a lower-bits D/A converter the same as the binary weight of the least significant bit of a higher-bits D/A converter.
Noguchi, U.S. Pat. No. 5,914,682, issued Jun. 22, 1999, also produces dual addresses in the output voltage, but without the necessity of providing a greater number of bits than the binary number to be D/A converted, and also without the exclusive OR logic of Clark et al. Instead, Noguchi uses a resistor to proportion output voltages of an upper-bits D/A converter circuit and a lower-bits D/A converter.
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 (VCO), 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.
Hulbert et al., in U.S. Pat. No. 4,810,974, issued Mar. 7, 1989, teaches algebraically summing UP/DOWN signals in a counter which has therein previously stored channelizing information that has been recalled from a random access memory (RAM), correcting the channelizing information for temperature drift, one bit at a time, while driving the output frequency with channelizing information that is held in a latch. That is, corrected channelizing information is developed by counting and subsequently storing in a RAM for use the next time the same frequency is accessed.
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.
In phase-locked oscillators, both a forward path and a 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-locked 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, DOWN, and/or ZERO error signals. D/A conversion changes the digitally integrated error signal into a voltage whi
Emhiser Research LTD
Jean-Pierre Peguy
Miller Wendell E.
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