Apparatus and method for a programmable clock generator

1. A digital circuit for generating a second frequency clock from a first frequency clock where the second frequency is a ratio N/M of the first frequency, where N and M are adjustable integers, N≦M/2 and M<2 B comprising:

an adder, one input being N and the other input from a register;

a modulo M function, said function receiving an adder output;

said register clocked by the first frequency clock and receiving the modulo M output, and,

a comparator clocked by the first frequency clock, said comparator receiving the register output and outputting the second frequency clock;

wherein said adder, function, register and comparator are B bits.

2. The digital circuit of claim 1 , wherein the operation of the comparator is a function of M.

3. A digital circuit for generating a sine wave of a second frequency from a first frequency clock where the second frequency is a ratio N/M of the first frequency, where N and M are adjustable integers, N≦M/2 and M<2 B comprising:

an adder, one input being N and the other input from a register;

a modulo M function, said function receiving an adder output;

said register clocked by the first frequency clock and receiving the modulo M output, and,

a look up table receiving the register output and outputting a corresponding magnitude to create the sine wave of the second frequency;

wherein said adder, modulo M function and register are B bits.

4. The digital circuit of claim 3 , wherein the look up table for each M has M/2 register values associated with a magnitude of a sine wave at M/2 increments.

5. A method for digitally generating a second clock from a source clock in a digital circuit, wherein the frequency of the second clock is N/M times the frequency of the source clock, where N and M are selectable integers comprising the steps of:

selecting an integer N;

selecting an integer M, where N≦M/2;

determining the Modulo M of a sum and providing the Modulo M as an input to a register;

outputting a second clock from a comparator if the register output is greater than M/2;

adding the output of the register to N to obtain the sum; and,

clocking the register and the comparator from the source clock;

thereby generating a second clock from the source clock.

6. The method of claim 5 wherein the register is a B-bit register and M≦2 B .

7. The method of claim 5 wherein the Modulo M is determined in a Modulo M function.

8. A Direct digital synthesizer for generating a clock signal with a frequency of N 1 /M 1 of a first clock frequency, having an adder, register and comparator, wherein the register and comparator are driven by the first clock, the adder adds N 1 and the output of the register and outputs the sum to the register which outputs B bits into the comparator and wherein N is selectable, the improvement comprising a modulo M circuit between the adder and the register and replacing the fixed comparator of M 1 with a variable M comparator, where M is selectable.

9. The synthesizer of claim 8 , wherein the variable M comparator further comprises a look up Sine table for each M.

10. A gateless digital circuit for generating a second clock with a frequency of N/M of the frequency of a first clock, wherein N and M are integers, N≦M/2 comprising a function, a register and a adder operable connected to generate the second clock, wherein both N and M are independently selectable, wherein most significant bit (MSB) of the register output is the second clock signal.

11. A digital circuit for generating a second frequency clock from a first frequency clock where the second frequency is a ratio N/M of the first frequency, where N and M are adjustable integers, N≦M/2 and 2 B >M≧(2 B −N) comprising:

an adder, one input being N and the other input from a register;

a modulo M function, said function receiving an adder output;

said register clocked by the first frequency clock and receiving the modulo M output, and,

outputting the second frequency clock as the most significant bit;

wherein said adder, modulo M function and register are B bits.