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Markus Loose STScI Calibration Workshop July 22, 2010

Application of the SIDECAR ASIC as the Detector Controller for ACS and the JWST Near-IR Instruments . Markus Loose STScI Calibration Workshop July 22, 2010. Outline. SIDECAR ASIC Architecture Overview Features Current SIDECAR Missions Performance Aspects Preamp/ADC Noise

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Markus Loose STScI Calibration Workshop July 22, 2010

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  1. Application of the SIDECAR ASIC as the Detector Controller for ACS and the JWST Near-IR Instruments Markus Loose STScI Calibration Workshop July 22, 2010

  2. Outline • SIDECAR ASIC Architecture • Overview • Features • Current SIDECAR Missions • Performance Aspects • Preamp/ADC Noise • Preamp offset drift • Reference/Bias voltage noise • Conclusion Scientific Detector Workshop, Garching, Germany

  3. SIDECAR ASIC Architecture System for Image Digitization, Enhancement, Control And Retrieval STScI Calibration Workshop

  4. SIDECAR ASIC Features • 36 analog input channels, each channel provides: • 500 kHz A/D conversion with 16 bit resolution • 10 MHz A/D conversion with 12 bit resolution • gain = 0 dB …. 27 dB in steps of 3 dB • optional low-pass filter with programmable cutoff • optional internal current source (as source follower load) • 20 analog output channels, each channel provides: • programmable output voltage and driver strength • programmable current source or current sink • internal reference generation (bandgap or vdd) • 32 digital I/O channels to generate clock patterns, each channel provides: • input / output / highohmic • selectable output driver strength and polarity • pattern generator (16 bit pattern) independent of microcontroller • programmable delay (1ns - 250µs) • 16 bit low-power microprocessor core (single event upset proof) • responsible for timing generation and data processing • 16 kwords program memory (32 kByte) and 8 kwords data memory (16 kByte) • 36 kwords ADC data memory, 24 bit per word (108 kByte) • additional array processor for adding, shifting and multiplying on all 36 data channels in parallel (e.g. on-chip CDS, leaky memory or other data processing tasks) STScI Calibration Workshop

  5. “SIDECAR ASIC” Missions ACS (HST) in space NIRCam/NIRSpec/FGS (JWST) in development TIRS (LDCM) in development STScI Calibration Workshop

  6. Noise Reduction by Using Multiple ADC Channels • PreAmp inputs shorted to ground (lowest noise signal in order to be dominated by ADC noise) • PreAmp gain set to 4 (12 dB) • Noise measured by using multiple preamp and ADC channels in parallel (1, 2, 4, 6, and 8) • Noise reduces almost as the square root of the number of channels used 1 ADC 2 ADCs 4 ADCs 6 ADCs 8 ADCs STScI Calibration Workshop

  7. Preamp Drift and Mitigation Data taken as 512 x 64 frames for efficiency, Gain = 4 σ= 52 ADU Drift kTC row noise σ= 13.9 ADU kTC removed (CCD mode) σ= 2.6 ADU STScI Calibration Workshop

  8. Bias Generator Noise • Bias output 1 routed back into PreAmp • PreAmp gain set to 22 (27 dB) • Use 4 ADCs in parallel to reduce PreAmp & ADC noise • Noise on bias without filtering is about 35µV (11.6 ADU) • Noise can be reduced by RC filtering to less than 5µV Unfiltered Noise of Bias Output 1 Bias noise as a function of RC filter time constant Filtered Noise of Bias Output 1 (tRC = 360 ms) PreAmp & ADC noise floor STScI Calibration Workshop

  9. Noise Power Spectrum of the Bias Outputs FFT of temporal noise measurement with RC filter set to tRC= 3 µs FFT of temporal noise measurement with RC filter set to tRC= 3 ms STScI Calibration Workshop

  10. Noise Power Spectrum of the Bias Outputs, Part 2 FFT of temporal noise measurement with RC filter set to tRC= 360ms FFT of temporal noise measurement with grounded PreAmp inputs (i.e. noise floor) STScI Calibration Workshop

  11. 1/F Noise in NIRSpec/JWST • Traditional CDS • Optimal CDS σCDS ~ 18 e- rms σCDS ~ 8 e- rms STScI Calibration Workshop

  12. ACS 1/f Noise STScI Calibration Workshop

  13. ACS 1/f Noise Bias Frame without correction (superbias subtracted) Bias Frame with correction (superbias subtracted) STScI Calibration Workshop

  14. Conclusion • SIDECAR ASIC is a small, low power and highly programmable solution for operating scientific detectors • Current performance limitations • Bias voltages exhibit high 1/f noise, even after filtering • ADC noise higher than ideal 16-bit ADC • Methods for dealing with these limitations exist • Hardware: Filtering, Gain • ASIC firmware (assembly code): Averaging of channels • Post-processing: Correlated noise correction algorithms • New version of SIDECAR ASIC currently in design • Improved bias generator with 5x lower noise • Reduced ADC noise STScI Calibration Workshop

  15. First Image of the Repaired Advanced Camera for Surveys Barred Spiral Galaxy NGC 6217 Photographed on June 13 and July 8 2009

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