Electrical computers: arithmetic processing and calculating – Electrical digital calculating computer – Particular function performed
Reexamination Certificate
1999-09-07
2003-07-01
Ngo, Chuong Dinh (Department: 2124)
Electrical computers: arithmetic processing and calculating
Electrical digital calculating computer
Particular function performed
C708S271000
Reexamination Certificate
active
06587862
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to the field of electronic circuit devices, and more particularly to an apparatus and method for digitally synthesizing variable frequency sinusoidal waveforms.
2. Description of the Related Art
In electronic systems, in particular those which are used in the communications field, the requirement to generate sinusoidal waveforms of varying frequency is very prevalent. Elementary physics tells us that the most effective and efficient means of transmitting information over long distances—regardless of whether the medium of transmission is wire, air, water, or some other substance—is to encode the information for transmission such that it is represented in the form of a sinusoid.
Virtually every electronic communications product on the market today employs multiple circuits whose only function is to generate a sinusoidal waveform at a prescribed frequency. Radios require such circuits so that they can receive a transmission over a specific channel. Telephones utilize specified frequency tones to indicate dialing sequences. And wireless products such as cellular telephones and pagers modulate voice signals for transmission over narrow and constantly changing frequency bands using sinusoidal modulation components. Spread-spectrum portable telephones utilize sinusoidal components to modulate voice at rapidly changing frequencies between a base station and a hand-held receiver. The list goes on and on.
In fact, certain products, specifically portable phones, cell phones, and pagers, could never have been developed using early apparatus to synthesize variable frequency sinusoidal waveforms. These early frequency synthesizers consisted entirely of analog electronic components that were heavy, complex, costly, and required lots of power to operate. Moreover, once set to a prescribed frequency, they typically had to be periodically reset because they tended to drift in frequency when operating temperature changed or as a function of operating time.
But all this changed with the introduction of digital frequency synthesis techniques. Because of the precision, speed, and low power requirement of digital logic devices, digital frequency synthesizers can be produced that are precise, small, inexpensive, and that can be operated in conjunction with other circuits for acceptable time periods on battery power alone. The proliferation of cell phones and pagers in our present culture attests to the enabling features of digital frequency synthesis techniques.
A present day digital frequency synthesizer consists of a phase signal generator and a phase-to-amplitude converter. The phase signal generator is loaded with a value that corresponds to a desired sinusoidal output frequency. Then, in synchronization with a clock signal, the phase signal generator produces digital data words at the frequency of the clock signal that correspond to phase samples ranging between 0 degrees and 360 degrees of the desired output signal. For example, at a clock signal rate of 100 MHz, if the phase signal generator produces phase samples that are 36 degrees apart (i.e., 0°, 36°, 72°, etc.), then this sequence corresponds to a 10 MHz output frequency.
This synthesized phase signal is then converted to an output amplitude by the phase-to-amplitude converter. Typically, a number of amplitude samples, each corresponding to a specific phase angle value for the output sinusoid are stored in a memory device such as a read-only memory (ROM) within the phase-to-amplitude converter. The phase signal is used to address a specific amplitude sample, which is then provided in digital form to an analog-to-digital converter. The analog to digital converter then produces a continuous amplitude waveform, changing the amplitude magnitude with each cycle of the clock signal.
From the above discussion, one skilled in the art can deduce that the generation of low-distortion sinusoids demands that a large number of amplitude samples be available for output within the ROM. Yet the storage of many samples requires many storage locations, proportionately increasing the cost, complexity, and power requirements of the digital frequency synthesizer. Fortunately, several techniques have been developed in more recent years that exploit the quadrature symmetry of sinusoidal waveforms so that storage location requirements are decreased by 75 percent. In addition, other compression techniques have been provided that allow even further reductions in power and size. One such technique utilizes Taylor Series expansion terms to improve the resolution of an amplitude sample corresponding to an intermediate phase angle, that is, an angle that is in between two angle values mapped by the ROM. But one skilled in the art will appreciate that for generation of a sine wave, to employ a meaningful Taylor series approximation, a term corresponding to a cosine wave must also be generated. Taylor series techniques are effective, but they require that both sine and cosine amplitudes be generated.
In spite of the advantages afforded by present day digital frequency synthesis techniques, application demands for mobile, portable, hand-held, and battery operated products continue to force designers to seek synthesizers that are less complex, that are more reliable, that are more precise, that use less power, and hence, that are less costly.
Therefore, what is needed is a digital frequency synthesizer that further exploits the symmetries inherent in sinusoidal waveforms to achieve further amplitude storage compression.
In addition, what is needed is an apparatus for simultaneously synthesizing sine and cosine wave components that only requires generation of amplitudes corresponding to an octant ranging in phase from 0 to 45 degrees for each of the components.
Furthermore what is needed is an octant-based digital frequency synthesizer for providing spectrally pure sine and cosine wave outputs.
Moreover, what is needed is a method for producing a sinusoidal waveform that uses only sine and cosine amplitude samples corresponding to an octant ranging from 0 degrees to 45 degrees in phase.
SUMMARY OF THE INVENTION
To address the above-detailed deficiencies, it is an object of the present invention to provide a digital frequency synthesizer that is based upon octant symmetries observed in a sine wave and cosine wave, taken together.
Accordingly, in the attainment of the aforementioned object, it is a feature of the present invention to provide a frequency synthesizer for producing a sinusoidal waveform. The frequency synthesizer includes a phase signal and a phase-to-amplitude converter. The phase signal indicates a desired phase angle of the sinusoidal waveform. The phase-to-amplitude converter is coupled to the phase signal. The phase-to-amplitude converter provides a desired amplitude sample corresponding to the desired phase angle, where the desired amplitude sample is derived from amplitude samples corresponding to an octant of the sinusoidal waveform The phase-to-amplitude converter includes a Haar Transform-based coarse octant amplitude sample generator that computes Haar coefficients corresponding to the phase signal and transforms the Haar coefficients into the desired amplitude sample.
An advantage of the present invention is that it requires less power to operate than that which has heretofore been provided.
Another object of the present invention is to provide an apparatus for simultaneously synthesizing sine and cosine wave components that translates of sine and cosine amplitudes corresponding an octant ranging in phase from 0 to 45 degrees to an octant corresponding to a desired phase angle.
In another aspect, it is a feature of the present invention to provide a digital frequency synthesizer for simultaneously producing a sine wave and a cosine wave, the sine wave and the cosine wave being at a prescribed frequency. The digital frequency synthesizer has an amplitude sample generator, a symmetry controller, and interpolation logic. The amplitude sample generator computes Haar
Huffman James W.
Huffman Richard K.
Ngo Chuong Dinh
Spectral Logic Design
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