Dear Philip Wang
Thanks for the response. You are correct to say that only three references -VREF, +VREF and 0 are required for the MDAC circuit. These levels have a DC level that is different from zero [say VCM]. So, I need three references now, that is, VCM+VREF, VCM and VCM-VREF.
I need to put a "buffer" each between the references VCM+VREF and VCM-VREF and the DAC reference inputs to prevent the noise from MDAC from influencing other circuits that share these references.
I am facing problem in the design of this buffer and would appreciate if you could help me with some references.