This note shows the block diagram of how a better common voltage
reference will be used for the next revision of the ADC and DAC boards
of the readout.
The 1/f performance of our readout system based on the ROACH system and
Raffanti's ADC and DAC boards appears to be dominated by instability of
the internal ADC voltage reference that sets the overall voltage scale
of the ADC. Thus, the next revision will incorporate an independent
voltage reference that is routed to both the ADC and DAC so any
fluctuations will cancel out to first order.
Common voltage reference for ADC and DAC board: Common_Vref_Circuit.pdf
Lab modification picture 2010/09/26: Common_V_ref.pdf