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Dynamic Offset Correction for Improvement of

Dynamic Range

Scott R. Johnston

SLAC

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Overview

Current ADC setup

Addition of dynamic offset to current setupSimulated Results

Different feedback algorithms and their results

Conclusions

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Existing SetupBlock Diagram

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Existing SetupTrace

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Proposed SetupBlock Diagram

ADC Common Mode range: 1V

ADC Differential range: 500mV

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Proposed SetupSimulated Feedback

Twice the gain, twice the dynamic range, still well within full range

(±127 counts)

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Proposed SetupSimulated Feedback: Offset

Settling time of ≈60 turns

Can be fixed by setting initial offset or changing time constant

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Feedback Algorithm

Average over all 16 slices

Average over past 16 turns

Apply this value times constant (1.3) to get offset

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Fast Feedback Algorithm

Average over all 16 slices

Average over past 2 turns

Apply this value times constant (1.3) to get offset

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Fast FeedbackSimulated Fast Feedback: Offset

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Fast Feedback Algorithm

Reconstruction of original data is essential

Not the case with slow feedback

As long as DAC works properly, reconstruction is trivial

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Summary and Conclusions

Dynamic Range can be improved by ≈ x2

If no initial offset value is provided, some data is lost on first fewturns

Number of turns depends on time constant of algorithm

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Other possibilities

fast algorithm at first, then slow later? (assuming ok load onFPGA)

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