Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Synthesizer
Reexamination Certificate
1999-11-01
2001-11-20
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Synthesizer
C327S129000, C327S113000, C327S107000, C331S061000, C708S270000, C708S276000
Reexamination Certificate
active
06320431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to numerically controlled oscillators. In particular, the invention relates to multifunctional numerically controlled oscillators that concurrently generate more than one waveform.
2. Description of the Related Art
FIG. 1
shows an example of how a cosine waveform may be stored for retrieval and reproduction by a circuit device. A cosine waveform
28
may be stored as a plurality of stored numerical cosine values
30
. The quantity of stored numerical cosine values
30
may be increased as desired for more accurate representation of the cosine waveform
28
. The cosine waveform
28
is periodic, so a periodic cosine signal may be reproduced by generating a signal having amplitudes corresponding to the stored numerical cosine values
30
.
Because the cosine waveform
28
is symmetric, it is not necessary to store all of the stored numerical cosine values. One period of the cosine waveform
28
may be divided into four quadrants
20
,
22
,
24
and
26
. Only the stored numerical cosine values
30
that are in the first quadrant
20
must be stored. To produce the stored numerical cosine values
30
in the second quadrant
22
, the values of the first quadrant
20
may be used, but in reverse order and with a sign change. To produce the stored numerical cosine values
30
in the third quadrant
24
, the values of the first quadrant
20
may be used, but with a sign change. To produce the stored numerical cosine values
30
in the fourth quadrant
26
, the values of the first quadrant
20
may be used, but in reverse order. Thus, only one-fourth of the stored numerical cosine values
30
must be stored in memory, which reduces the amount of memory required.
However, issues arise when a user would like more than one similar waveform to be generated concurrently; for example, if a sine waveform
32
having the same period is desired in addition to the cosine waveform. Such a sine waveform is merely the cosine waveform
28
with a phase shift of one quadrant. Therefore, it is not theoretically required to store any more values than the stored numerical cosine values in one quadrant (e.g., the first quadrant
20
).
However, when putting the theory into practice, a number of concerns arise. Since two waveforms are desired, the memory containing the stored numerical values
30
must be accessed twice for each output cycle. One way to access two values at once is to provide a second memory containing duplicate values, and to access each memory on each output cycle. However, this doubles the amount of memory required. A second potential solution is to use only one memory, but to access it with a doubled clock speed. This effectively accesses two of the stored numerical values on each output cycle. However, the technology used may not allow the memory to operate at twice the clock speed, or there may be a penalty of increased power for operating the memory at twice the speed.
Therefore, there is a need to generate multiple similar waveforms (e.g., a sine and a cosine) without additional memory or clocking requirements.
SUMMARY OF THE INVENTION
The present invention addresses these and other problems of the prior art by providing an apparatus for and method of generating numerically controlled oscillator signals.
According to one embodiment, an apparatus according to the present invention includes a plurality of storage elements, at least one selector circuit, and at least one inverter circuit. The plurality of storage elements is configured to store a plurality of values corresponding to a portion of a periodic waveform and to receive an addressing signal, and in accordance therewith generate a plurality of first output signals, wherein each of the plurality of storage elements is configured to generate one of the plurality of first output signals corresponding to an addressed one of the plurality of values. The at least one selector circuit is coupled to the plurality of storage elements and is configured to receive at least one select signal and the plurality of first output signals, and in accordance therewith generate a plurality of second output signals, wherein each of said plurality of second output signals corresponds to a selected one of the plurality of first output signals. The at least one inverter circuit is coupled to the at least one selector circuit and is configured to receive the plurality of second output signals and a plurality of polarity signals, and in accordance therewith generate a plurality of final output signals, wherein each of said plurality of final output signals corresponds to one of the plurality of second output signals and to the periodic waveform.
According to another embodiment, a method according to the present invention includes the steps of storing a plurality of values corresponding to a portion of a periodic waveform; and receiving an addressing signal and in accordance therewith generating concurrently a plurality of first output signals, wherein each of the plurality of first output signals corresponds to an addressed one of the plurality of values. The method further includes the step of receiving at least one select signal and in accordance therewith generating a plurality of second output signals, wherein each of the plurality of second output signals corresponds to a selected one of the plurality of first output signals. The method still further includes the step of receiving a plurality of polarity signals and in accordance therewith generating a plurality of final output signals, wherein each of the plurality of final output signals corresponds to one of the plurality of second output signals and to the periodic waveform.
A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description and accompanying drawings which set forth illustrative embodiments in which the principles of the invention are utilized.
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Potson David
Rives Mark F.
Callahan Timothy P.
Girard & Equitz LLP
National Semiconductor Corporation
Nguyen Minh
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