Patent GB-1134055-A (GB)
Title: Improvements in or relating to signal generators
Inventor: GIBSON RODNEY WILLIAM
IPC: G06F1/02
Filed: 1966-02-04
Abstract: 1,134,055. Processing digital signals. MULLARD Ltd. 4 Feb., 1966, No. 5119/66. Heading G4A. An apparatus for generating sequences of samples of a set of " N " periodic waves having fundamental frequencies spaced by equal amounts "f" includes a clock 1 of beat frequency Na, where a = 2Nf, which sends signals to an adder 4 and a divider 3, the latter directing every Nth pulse to a counter 2 and to a register 5 of capacity 2N. For every beat of the clock a signal via lead 7 actuates adder 4 to cumulatively add into register 5 the contents of counter 2, every Nth signal being transmitted by the divider 3 to increment the counter 2 and to set the register 5 to zero. If the contents of counter 2 at the beginning of a cycle is " i ", then after " j " beats of the clock (j <( N), since the capacity of the register is just 2N, it will contain at that instant the number 2N. [fractional part of (ji/2N)] which, assuming the lowest frequency of a set of N periodic waves having frequencies spaced by equal amounts " f " is " kf " where " k " is any integral multiple of a, corresponds to the phase of the jth wave in the ith cycle when the waves are generated in sequence, in ascending frequency order, and the frequency of generation corresponds to the beat of the clock 1. Thus if at a particular beat of the clock the register 5 is 1/xth full then the phase of a wave corresponding to that beat is 1/xth of a cycle. If the accumulator comprising adder 4 and register 5, is a binary accumulator, and has S digits it will therefore determine the phase of a corresponding wave to one (2<SP>s</SP>)th of a cycle, and therefore determining means 9 connected to the " n " most significant digits of the register 5, may be arranged to transmit signals to a translator 10 corresponding to (<SP>1</SP>/ 2 )th part of the phase of a particular wave, the translator then transmitting the appropriate quantized amplitude level of that wave. If the frequency of the lowest wave is pf where p is not an integral multiple of a, then to represent the phase of the jth wave in the ith cycle, the register 5 should contain the number 2N [fractional part of and to accomplish this further registers (11, 13) (Fig. 2, not shown) and adders (12, 18) are provided to add the number pi into the register (15). Further translators may be incorporated to transmit simultaneously the amplitude levels of waves having identical phase but varying waveform. Alternatively the levels of two waves of identical shape but of different phase, may be transmitted alternately by a single translator receiving signals alternately from register 5 and a further register, which latter register is incremented by an amount corresponding to the phase difference in the two waves. In a further arrangement the frequency of the clock 1 and the capacity of the accumulator 4, 5 are doubled and the output of the translator arranged to give alternate sequences of sine and cosine waves. The generator may form part of a Fourier analyser for deriving the spectral components of an unknown wave, the output components of generator corresponding to one particular wave frequency being multiplied by the unknown wave and then integrated to give the spectral component of the unknown wave corresponding to that particular frequency.