Suppression of spatial and temporal noise in a CMOS image sensor
Shuang Xie (TU Delft - Electronic Instrumentation, IMEC)
A.J.P.A.M. Theuwissen (Harvest Imaging, TU Delft - Electronic Instrumentation)
More Info
expand_more
Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons.
Abstract
This paper presents methodologies for suppressing the spatial and the temporal noise in a CMOS image sensor (CIS). First of all, it demonstrates by using a longer-length column bias transistor, both the fixed pattern noise (FPN) and temporal noise can be suppressed. Meantime, it employs column-level oversampling delta-sigma ADCs to suppress temporal noise as well as to facilitate the realization of the thermal compensation of dark signal non-uniformity (DSNU). In addition, the image pixels are re-configured as temperature sensors with inaccuracies within ±0.65 °C, between -20 and 80 °C. If the dark current and its non-uniformities are caused by thermal gradients, the obtained in-pixel thermal information can be employed to compensate for the measured dark current by 95 % and DSNU, up to 13 %. All the column-level 13 bit 2
nd-order incremental delta-sigma ADCs are measured with SNR around 65 dB and INL around 1.5 LSB, when tested with a -8 dB input signal and sampling at 2 MHz with an oversampling ratio (OSR) of 128, when the full scale voltage is 2 Vp-p. The 4T Pinned Photodiode (PPD) CIS is measured to have a temporal noise of 34~\mu \text{V} rms (with an OSR of 128, or, an input referred temporal noise of 0.5 e
- rms, with a conversion gain, CG, of 73~\mu \text{V}/ \text{e}^{-} ), a column gain FPN of 0.06 %, a dynamic range (DR) of 92 dB (with OSR = 512), as well as a linearity of 1 %. It has a measured DSNU of 3.2 %, after the thermal compensation using the in-pixel temperature sensors, a dark current of 290 pA/cm
2 and 15 pA/cm
2, measured at 60 °C, before and after the thermal compensation, respectively.