2nd order sigma delta DAC

[zhangseong]

i am currently studying on this sigma delta DAC
in the 2nd order form , what is the " ??" i point to? anyone know?

 

[Btrend]

it is a feedback gain, and gain is 2

 

[zhangseong]

how to implement the gain of 2? what i know is, for the unity gain, the feedback digital value must be negative of the input range. for example, if the input is 4 bit(0-15), the feedback must be in the range of 0 to -16.
so, for the gain of 2, does that mean that the range of the feedbank signal must be twice the input (0 to -32)?

 

[Btrend]

since ur feedback is negative (there is a minus sign around the adder), so ur feedback signal should be positive, otherwise it will become positive feedback.
shift left a bit will equivalent to multiply by 2.