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Video Post Processor

Video Post Processor. Stephen Kaye 2013-3-28. Preamp Design – Review. Preamp based on instrumentation amp Preamp gain set to 2 V/V Input referred noise 40 nV/√Hz Impedance matched to 100 Ω lines Preamp delivers fully differential signal. Video Processor Design. Filter Reset.

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Video Post Processor

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  1. Video Post Processor Stephen Kaye 2013-3-28

  2. Preamp Design – Review • Preamp based on instrumentation amp • Preamp gain set to 2 V/V • Input referred noise 40 nV/√Hz • Impedance matched to 100 Ω lines • Preamp delivers fully differential signal

  3. Video Processor Design Filter Reset Differential Input from Preamp ADC Differential Amplifier Common Mode Feedback

  4. Video Processor – Differential Amplifier • Differential Buffer AD4938-1 • Two output terminals +OUT and –OUT • Outputs are 180º out of phase • Two feedback loops • Input to set common mode voltage

  5. Video Processor – Differential Amplifier

  6. Video Processor – Differential Offset

  7. Video Processor – CM Offset • Common mode output set by Vocm input • Common mode set by ADC to Vref/2 • Additional ADC adjustment available Vocm Feedback

  8. Video Processor – Noise • Differential noise model • Voltage noise • Current noise • Resistor noise • Well matched resistors eliminate common mode voltage noise

  9. Video Processor - Noise • Resistor noise e = √4kTR • Each input has multiplication factor for output • GN = 2 • β = 0.5

  10. Video Processor - Noise • Output noise total is sum of squares of contributions • Total output voltage noise 20.22 nV/√Hz • Total output voltage noise from preamp 57.3 nV/√Hz • Sum of noise is 60.76 nV/√Hz

  11. Video Processor – Anti-Aliasing Filter • Simple single pole RC filter • ADC sampling frequency is 6MHz • Anti-aliasing filter 3dβ set to 3 MHz • Filter resistor noise is 0.46 nV/√Hz – negligible • Filter reset by switch to ground with Ron = 1Ω

  12. Video Processor – ADC Sampling • 6x oversampling of 1 MHz pixel rate • Three reset signal samples and three charge signal samples • Samples are averaged for reset signal and charge signal • Effectively creates another filter pole at 3 MHz • CDS performed using averaged reset signal and charge signal for each pixel

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