Sine wave generator with dual port look-up table

A method of generating a cyclical signal, the method comprising:

• a) generating a series of addresses at periodic intervals;
• b) producing a shifted series of addresses from the series of addresses;
• c) reading a first series of values through a first port of a memory, the values in the first series being read from the memory at addresses in the series of addresses, and reading a second series of values through a second port of the memory, the values in the second series being read from the memory at addresses in the shifted series of addresses;
• d) obtaining a third series of values based on the first series of values and the second series of values;
• e) computing a fourth series of values by combing the third series of values with at least the first series of values;
• and
• f) applying the fourth series of values to a digital to analog converter.

An automatic test system, comprising a direct digital synthesis circuit adapted to generate a cyclical signal, the direct digital synthesis circuit comprising:

• a) an accumulator having an output;
• b) a memory comprising a first address input and a second address input and a first output and a second output, the first address input being coupled to the output of the accumulator, and the memory storing values representing at least a portion of the cyclical signal;
• c) a shifter coupled between the output of the accumulator and the second address input of the memory;
• d) a circuit having a first input and a second input coupled to the first output and the second output, respectively, of the memory, the circuit having an output based at least in part on a combination of values responsive to the first input and the second input;
• and
• e) a digital to analog converter coupled to the output of the circuit.