Patent
1979-12-31
1982-09-14
Popek, Joseph A.
328 27, H04M 150
Patent
active
043497047
ABSTRACT:
Multifrequency (FIGS. 2 and 4) signals are generated by employing a microcomputer system (500) in conjunction with a digital-to-analog converter (506) and filter (507). Digital representations of amplitude values of the signals to be generated are stored in a read only memory (ROM 503) and sampled at a predetermined rate under control of a central processor unit (CPU 502) to generate digital signals representative of the desired multifrequency signal. The sampling rate is selected to be less than the theoretical Nyquist rate for the highest frequency tone in the multifrequency signal to turn to account the resulting so-called "alias" signals for generating tones closely spaced in frequency. In a specific example, the sampling rate is equal to twice the average frequency of the tones in the desired multifrequency signal. Unwanted harmonic components (3.omega..sub.0, etc.) in the resulting multifrequency signal are minimized by employing a sampling interval which is in a predetermined relationship to the average frequency of the tones in the desired multifrequency signal. In a specific example, the sampling interval is equal to the reciprocal of three times the average frequency of the multifrequency signal.
REFERENCES:
patent: 3959604 (1976-05-01), Newsom et al.
patent: 4017693 (1977-04-01), Roche et al.
patent: 4171466 (1979-10-01), Carbrey
patent: 4227248 (1980-10-01), Munter
Bell Telephone Laboratories Incorporated
Padnes David R.
Popek Joseph A.
Stafford Thomas
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