Digital sine wave synthesizing method and apparatus

Abstract

A simple method and apparatus for generating approximate sine waves is described. A digital accumulator or adder is driven at a basic counting rate to accumulate increments representative of phase with the total sum representative of total phase angle of a sine wave. The output is periodically sampled and the value is converted into an analog output voltage in a normal D to A converter. A straight line ramp voltage approximation to the sine wave function is created as the result. The accumulator operates in this fashion until a total phase angle of approximately 45.degree. is accumulated. Then accumulation value additions are then accorded 1/2 their usual significance until 671/2.degree. of total phase angle are accumulated. Then accumulation is then at 1/4 the basic significance accorded to increments until 90.degree. is reached. The symmetry of the sine wave allows the 0.degree. through 90.degree. samples to be used to generate the full 360.degree. wave form by simple inversion or reverse counting of the counter and inversion of the algebraic sign as necessary. A binary slope approximation to the sine function is achieved by this technique. A series of straight line slopes with a slope of 1, 1/2 and 1/4 are utilized to approximately track a true sine function. The breaks in slope occur in a binarily related fashion to a 90.degree. quarter cycle at 90.degree./2 and at 90.degree./4. These simple binary relationships allow the sine function to be approximated very easily by discrete logic and simple binary counters or parallel adders or by the equivalent counting in registers of a microprocessor. The resulting output is applied to a D to A converter to derive the output analog voltages.