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Improving the Zero Crossing Performances in a Digital Sine Wave Generator

IP.com Disclosure Number: IPCOM000080632D
Original Publication Date: 1974-Jan-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Peard, M: AUTHOR

Abstract

This description is directed to a method for generating sine waves by using a read-only memory, wherein a binary pattern corresponding to a quarter of period is stored.

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Improving the Zero Crossing Performances in a Digital Sine Wave Generator

This description is directed to a method for generating sine waves by using a read-only memory, wherein a binary pattern corresponding to a quarter of period is stored.

According to this method, to generate a sine wave having any frequency F, a N-bit pattern is read out of the memory as a function of this frequency, and the symmetry properties of such a wave are used to reconstruct the whole period from the quarter of period.

The reading operation is performed under the control of a clock running at a high frequency Fc. For frequency F, the duration of the quarter period is:. T = 1 over 4F This duration corresponds to a number Nc of clock impulses: Nc = Fc over 4F.

To obtain the greatest accuracy, the value taken for Nc is the better approximating integer corresponding to the exact ratio Fc/4F. This approximating integer is chosen as follows:

If Fc over 4F is not an integer, it satisfies the following inequality:

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The number of clock impulses per bit of the pattern is: Nb = Fc over 4NF = Nc over N which is not an integer for any F and N.

Consequently to improve the zero crossing performances, a number k of bits of the pattern is extracted from the memory using a bit rate equal to the integer part of Nb:Q, and the number (n-k) of remaining bits is extracted from the memory using the bit rate Q + 1.

This number k is calculated for any frequency F to be generated by solving the...