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A new two-step Σ∆ architecture column-parallel ADC for CMOS image sensor

Abstract : The demand for high resolution CMOS image sensors (CIS) is rising. Analog-to-digital converters (ADC) represent one of the major bottleneck of CIS. One of the candidates to overcome the existing limits is the column-parallel ADC. Column-parallel extended counting ADCs (EC-ADC) are able to reach high resolution thanks to their two-step conversion. However the EC-ADC area increases due to the two-step design. A solution is to use the same hardware twice to perform both steps. This paper proposes a 14-b, 100 kHz Nyquist frequency, two-step incremental Σ∆ (IΣ∆) analog-to-digital converter suitable for column-parallel CIS. Several architectures with different modulator order are compared to determine the most promising one. The proposed architecture, compared to a one-step second order modulator, reduces the total oversampling ratio (OSR) from 150 to 60 to reach a resolution of 14-b. The operational transconductance amplifiers (OTA) is the most critical part in our ADCs. Its required DC-gain is around 80 dB for a 120 MHz gain-bandwidth product (GBW). The ideal DNL and INL of our two-step IΣ∆ ADC are respectively +0.55/-0.6 LSB and +0.5/-0.5 LSB. This work achieves a SNDR of 89 dB when a full scale sinusoid of 100 kHz is applied. Index Terms—ADC, incremental, sigma-delta (Σ∆), two-step, CMOS Image Sensor, column-parallel ADC, second-order Σ∆
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Submitted on : Thursday, September 1, 2016 - 10:29:07 AM
Last modification on : Wednesday, September 16, 2020 - 5:49:16 PM
Long-term archiving on: : Friday, December 2, 2016 - 4:08:21 PM

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Pierre Bisiaux, Caroline Lelandais-Perrault, Anthony Kolar, Philippe Benabes, Filipe Vinci dos Santos. A new two-step Σ∆ architecture column-parallel ADC for CMOS image sensor. 2016 29th Symposium on Integrated Circuits and Systems Design (SBCCI) , Aug 2016, Belo Horizonte, Brazil. ⟨10.1109/SBCCI.2016.7724065⟩. ⟨hal-01357892⟩

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