Patent ID: 7307568

Claim:
A method to eliminate inter-symbol interference error at an I-to-V output stage of a current steering DAC having a plurality of current cells, said output stage comprising at least an I-to-V amplifier having summing junctions SJP and SJN, feedback resistances R 1 and R 2 , and feedback capacitances C 1 and C 2 , said method comprising the steps of: disconnecting said feedback resistors R 1 and R 2 and said current cells from said summing junctions SJP and SJN of said amplifier in said output stage; connecting said feedback resistors R 1 and R 2 together to form a resistor string across outputs of said output stage, with said feedback capacitors C 1 and C 2 creating a hold period to hold output voltage of said I-to-V amplifier when said I-to-V amplifier is not connected to said current cells of said current steering DAC; using the I-to-V amplifier as a buffer to maintain a CM level at drains of said current cells during said hold period by connecting the outputs of said current cells to midpoint of said resistor string; and changing DAC codes while outputs of said current cells are in said hold mode, and disconnecting the outputs of said current cells from each other after the DAC codes are changed and re-connecting said feedback resistors and appropriate outputs of said current cells back to the summing junctions of said I-to-V converter.