Digital generator for producing a sinewave

Claim 2

A digital generator for producing a sinewave in the form of a succession of digitally encoded samples produced with a sampling period T, the sinewave having an amplitude R and a phase difference φ between two successive samples, the sinewave at time k defined by the vector sum A k +jB k =Re jk φ the generator comprising: means for generating signals a=cos φ, b=sin φ, A k , B k at time k, where A o =R and B o =0 at time 0; first signal processing means (5, 7, 3, 6, 8, 4) for combining said signals a, b, A k and B k for providing signals aA k -bB k , and bA k+aB k , at time k; second signal processing means (18, 19, 15, 16, 27) responsive to said first signal processing means for providing a signal proportional to ##EQU8## at time k; and third signal processing means (24, 17, 25, 22, 23) responsive to said second signal processing means for providing signals ##EQU9##

Claim 3

A generator according to claim 1, wherein R=1.

Claim 4

A digital generator for producing a sinewave in the form of a succession of digitally encoded sample values A k and B k at successive instants k=0, 1, 2, . . . regularly separated by periods T, such that A k +jB k =Re jk φ, where R is the desired amplitude of the sinewave and φ is its phase difference between two successive samples, the generator comprising: primary calculation means including two registers (1, 2) for storing the current values of A k and B k , two registers for storing constants a and b (12, 11) such that a=cos φ and b=sin φ, multiplying means (5, 6, 8, 7) connected to said two registers storing A k and B k and said two registers storing a and b for calculating the products: aA k , bA k , aB k and bB k , and adding and subtracting means (3, 4) connected to said multiplying means for calculating approximations A' k+1 and B' k+1 to the next sample values A k+1 and B k+1 where: A'.sub.k+1 =aA.sub.k -bB.sub.k B'.sub.k+1 =bA.sub.k +aB.sub.k ; correction factor calculation means arranged to receive the approximations a' k+1 and B' k+1 and including multiplying/dividing means (18, 19, 24, 25) and adding/subtracting means (15, 16, 17) to calculate a correction factor (1-1/2ε k+1 ) therefrom, where ##EQU10## multiplication means (22, 23) arranged to receive said correction factor and the approximations A' k+1 and B' k+1 to calculate the next sample values: ##EQU11## means for replacing (1, 2) the sample values A k and B k by the sample values A k+1 and B k+1 in said registers for storing the current values in order to begin a further cycle of calculation; and initialization means (13, 14) providing an input to said primary calculation means for ensuring that the amplitude of the starting values A o and B o is greater than 0 and not greater than R√5.

Claim 5

A digital generator for producing a sinewave in the form of a succession of digitally encoded sample values A k and B k at successive instants k=0, 1, 2, . . . regularly separated by periods T, such that A k +jB k =Re jk φ, where R is the desired amplitude of the sinewave and φ is its phase difference between two successive samples, the generator comprising: primary calculation means including two registers (1, 2) for storing the current values of A k and B k , two registers for storing constants a and b (12, 11) such that a=cos φ and b=sin φ, multiplying means (5, 6, 8, 7) connected to said two registers storing A k and B k and said two registers storing a and b for calculating the products: aA k , bA k , aB k and bB k , and adding and subtracting means (3, 4) connected to said multiplying means for calculating approximations A' k+1 and B' k+1 to the next sample values A k+1 and B k+1 where: A'.sub.k+1 =aA.sub.k -bB.sub.k B'.sub.k+1 =bA.sub.k +aB.sub.k ; correction factor calculation means arranged to receive the approximations a' k+1 and B' k+1 and including multiplying/dividing means (18, 19, 24, 25) and adding/subtracting means (15, 16, 17) to calculate a correction factor (1-1/2ε k+1 ) therefrom, where ##EQU10## multiplication means (22, 23) arranged to receive said correction factor and the approximations A' k+1 and B' k+1 to calculate the next sample values: ##EQU11## means for replacing (1, 2) the sample values A k and B k by the sample values A k+1 and B k+1 in said registers for storing the current values in order to begin a further cycle of calculation; and initialization means (13, 14) providing an input to said primary calculation means for ensuring that the amplitude of the starting values A o and B o is greater than 0 and not greater than R√5.

Claim 6

A generator according to claim 3, wherein the initialization means sets one of A o and B o to R and the other to zero.

Claim 7

A generator according to claim 3, wherein the multiplying/dividing means comprising: means for squaring (18, 19) the approximate values to obtain A' k+1 2 and B' k+1 2 ; said adding/subtracting means comprising means for summing the said squares (15) to obtain (A' k+1 2 +B' k+1 2 ), means for subtracting (16) the sum of the squares from R 2 , to obtain R 2 -(A' k+1 2 +B' k+1 2 ); said multiplying/dividing means further comprising means for halving (24) the difference thus obtained to obtain ##EQU12## said adding/subtracting means further comprising means for adding the halved difference to R 2 to obtain ##EQU13## said multiplying/dividing means further comprising means for multiplying by 1/R 2 to obtain ##EQU14##

Claim 8

A generator according to claim 3, wherein the value of R is chosen to be unity.

Claim 9

A generator according to claim 3, wherein the primary calculation means, the correction factor calculation means and the multiplication means are all constituted by a single, program-controlled processor, which performs all the said operations sequentially within each period T.

Claim 10

A generator according to claim 3, wherein the period T corresponds to a sampling frequency of not less than 4,800 Hz.

Claim 11

A generator according to claim 3, wherein calculations are performed in binary using 16 bit two's complement arithmetic.