Differing frequency sine wave generation from a look-up table
First Claim
1. A method for generating at least two different frequency sine waves for transmission at a first frequency from a look-up table having entries including samples taken at a second sampling frequency which is not an integral multiple of said first frequency, said method comprising the steps of:
- selecting a fundamental table frequency such that the frequencies of said different frequency sine waves to be generated are each an integral multiple of said fundamental table frequency;
determining a fractional correction factor by;
placing said second sampling frequency over said first frequency to form a fraction; and
reducing said fraction;
forming a look-up table for a sine wave of said fundamental table frequency by taking samples at a rate equal to said second sampling frequency times a denominator of said fractional correction factor;
accessing said look-up table using at least two different table steps corresponding to said at least two different frequency sine waves to be generated; and
taking first and second fractional portions of two different table steps for transitions between corresponding first and second frequency sine waves, said first and second fractional portions summing to one.
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Accused Products
Abstract
Sine waves are generated by a port circuit processor of a telephone switching office by accessing a look-up table stored in a memory associated with the port circuit processor. Entries in the look-up table are accessed by using table steps or Δ'"'"'s which correspond to the frequencies of the sine waves to be generated. The table steps or Δ'"'"'s are changed for different sine wave frequencies and may be changed each bit period. Whether changed or not, a first fractional portion of the table step or Δ for the previous frequency is combined with a second fractional portion of the table step or Δ for the current frequency with the first and second fractional portions adding up to one. In this way, an X sample per second data stream, X equaling the base sample rate of the look-up table, that precisely matches a Y bits per second rate, Y equaling the transmission rate of the data stream, is generated.
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Citations
18 Claims
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1. A method for generating at least two different frequency sine waves for transmission at a first frequency from a look-up table having entries including samples taken at a second sampling frequency which is not an integral multiple of said first frequency, said method comprising the steps of:
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selecting a fundamental table frequency such that the frequencies of said different frequency sine waves to be generated are each an integral multiple of said fundamental table frequency; determining a fractional correction factor by; placing said second sampling frequency over said first frequency to form a fraction; and reducing said fraction; forming a look-up table for a sine wave of said fundamental table frequency by taking samples at a rate equal to said second sampling frequency times a denominator of said fractional correction factor; accessing said look-up table using at least two different table steps corresponding to said at least two different frequency sine waves to be generated; and taking first and second fractional portions of two different table steps for transitions between corresponding first and second frequency sine waves, said first and second fractional portions summing to one. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for generating at least two different frequency sine waves for transmission at a first frequency from a look-up table having entries including samples taken at a second sampling frequency which is not an integral multiple of said first frequency, said method comprising the steps of:
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selecting a fundamental table frequency such that the frequencies of said different frequency sine waves to be generated are each an integral multiple of said fundamental table frequency; determining a fractional correction factor by; placing said second sampling frequency over said first frequency to form a fraction; and reducing said fraction; determining a new fundamental table frequency by multiplying said fundamental table frequency by said denominator of said fractional correction factor; forming a look-up table for a sine wave of said new fundamental table frequency by taking samples at a rate equal to said second sampling frequency; determining at least two different table steps corresponding to said at least two different frequency sine waves to be generated; accessing said look-up table using said at least two different table steps; and taking first and second fractional portions of two different table steps for transitions between corresponding first and second frequency sine waves, said first and second fractional portions summing to one. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A method for generating at least two different frequency sine waves for transmission at a first frequency from a look-up table having entries including samples taken at a second sampling frequency which is not an integral multiple of said first frequency, said method comprising the steps of:
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selecting a fundamental table frequency such that the frequencies of said different frequency sine waves to be generated are each an integral multiple of said fundamental table frequency; determining a fractional correction factor by; placing said second sampling frequency over said first frequency to form a fraction; and reducing said fraction; forming a look-up table for a sine wave of said fundamental table frequency by taking samples at a rate equal to said second sampling frequency times a denominator of said fractional correction factor; accessing said look-up table using at least two different table steps corresponding to said at least two different frequency sine waves to be generated; and taking first and second fractional portions of two table steps occurring on either side of transmission transition points defined by said first frequency, said first and second fractional portions summing to one. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification