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18 Bit ADC Status

The ADC collaboration meeting held on May 18, 2007, focused on early test results primarily conducted by Luis. Key findings included good pedestal noise performance, isolated channels with no significant crosstalk, and acceptable differential non-linearity. Noteworthy challenges included negative pedestals and difficulties in using the ADC with the timing board, which affected data integration. Future improvements will address regulator separation to minimize crosstalk and implement adjustments for negative pedestals through DAC. A full report will follow, and a prototype board is expected next week.

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18 Bit ADC Status

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  1. 18 Bit ADC Status Collaboration meetingMay 18, 2007

  2. Early Tests (mostly by Luis) • Pedestal Noise good • Channels are isolated • No apparent crosstalk • More later • Differential Non-Linearity OK • Gave a smooth response to a time varying input

  3. DAC noise works • Multiple sampling of base and peak reduce noise • Causes other issues • Still have negative pedestals • A full report will be written

  4. Lead Run • We didn’t know how to use ADC with timing board • Used internal timing but had a mistake

  5. Error: we were integrating over the HV transition • Led to a pair ordered asymmetry • Problem was resolved but never received low background data.

  6. External timing • Working on getting the busy logic right • Oversample=0 (one sample per cycle): • Integrated value proportional to window

  7. Busy time proportional to sum of ramp delay and window • CODA working for oversample=0 and timing board

  8. Oversampling • Busy Logic working • 256 word readout limit • Becomes an issue when doing many oversample and multiple samples • Not really a problem because we don’t have to flush out ALL data • Means we have to assume that ADC is working correctly for this data (which it is for few oversamples) • Tested in Stand-alone code, presently incorporating into CODA

  9. Future • Prof. Wilson: Separate the regulators between ADC channels, will be done on the next board • Ensures no crosstalk • Voltage mode • Nearly infinite impedance • Current mode • Works best as current through a resistor

  10. Pedestals • The pedestals are negative, but can and will be adjusted • Next week will be receiving a prototype board with a resistance pots which will be adjusted on a channel by channel basis so that pedestals are small and positive • In Future Pedestals will be adjusted by a DAC • Next Board available in August

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