Hi all,

I'm using a 2nd-order digital error feedback noise shaper in my resistor devider DAC design. But I find that if I first input a signal to the noise shaper, and then cut this signal off to a zero or just a DC code, I would get a tone at the output of the noise shaper, and the tone frequency would change with the input DC level. I have tried to use a (pseudo-random) dither signal at the input of the noise shaper or before the bit-splitter (into MSBs and LSBs) inside the noise shaper. For some input DC levels, the dither can remove the tone, but for some others, the tone could still appear.

Certainly I can remove the tone if I cut off the error-feedback loop when the noise shaper input is a DC signal, but does anyone know that if it's possible to remove this idle-channel tone with (what kind of) a dither signal, and where should I inject this dither signal for this kind of noise shaping architecture?

Thanks in advance!

CC