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18 Bit ADC Status

18 Bit ADC Status. Collaboration meeting May 18, 2007. 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. DAC noise works

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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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