Selectable Logarithmic/Linear Response Active Pixel Sensor Cell with Reduced Fixed-Pattern-Noise Based on Dynamic Threshold MOS Operation

Abstract

A selectable logarithmic/linear response active pixel sensor cell with reduced fixed-pattern-noise is proposed. It is composed of four dynamic threshold metal-semiconductor-oxide field-effect transistors (DTMOSs), which have inherently fewer characteristic fluctuations than conventional bulk counterparts. Therefore this proposed active pixel sensor cell is expected to reduce fixed-pattern-noise as compared with that of a device composed of bulk metal-oxide-semiconductor field effect transistors (MOSFETs) without any external noise reduction circuitry particularly in the logarithmic response mode. The effectiveness of the proposed sensor cell is partly experimentally verified using test devices that simulate the readout portion of the proposed sensor cell.

Novel Operation Scheme for Realizing Combined Linear-Logarithmic Response in Photodiode-Type Active Pixel Sensor Cells

“…Logarithmic transformation is a method of overcoming such a drawback, an APS cell with a selectable linear/logarithmic response has been proposed. 4) Although it realizes two distinct operation modes with either linear or logarithmic response, 4) it is not possible to directly combine two images obtained in each response mode because their output signal levels differ in either mode.…”

A Wide-Dynamic-Range Photodiode-Type Active Pixel Sensor Cell with Seamlessly Combined Logarithmic–Linear–Logarithmic Response

“…2) Logarithmic transformation 1) is one solution for the dynamic range widening of APSs. Thus the authors have proposed, first, an APS cell with selectable linear/logarithmic response, 3) and second, the operation scheme that realizes seamlessly combined linearlogarithmic response in photodiode-type (PD) APS cells. 4) Similar proposals have been made by other groups.…”

Temperature Dependence of the Subthreshold Characteristics of Dynamic Threshold Metal–Oxide–Semiconductor Field-Effect Transistors and Its Application to an Absolute-Temperature Sensing Scheme for Low-Voltage Operation

“…1, both band bending, S 0 , and gate depletion layer width, w 0 , in a DTMOS are always fixed due to the gate-to-body connection. 9,10) Therefore the surface potential change (Á S ) in a DTMOS is exactly the same as the gate voltage change (ÁV g ), i.e., Á S ÁV g . 5,9,10) Note that an alternative equation, 11) ( S : surface potential, B ¼ ðk B T=qÞ lnðN A =n i Þ, k B : Boltzmann constant, T: absolute temperature, q: elementary charge, N A : substrate impurity concentration, n i : intrinsic impurity concentration) both the DTMOS and the conventional MOSFET are considered to be in the subthreshold region where drain current varies exponentially with S .…”

“…9,10) Therefore the surface potential change (Á S ) in a DTMOS is exactly the same as the gate voltage change (ÁV g ), i.e., Á S ÁV g . 5,9,10) Note that an alternative equation, 11) ( S : surface potential, B ¼ ðk B T=qÞ lnðN A =n i Þ, k B : Boltzmann constant, T: absolute temperature, q: elementary charge, N A : substrate impurity concentration, n i : intrinsic impurity concentration) both the DTMOS and the conventional MOSFET are considered to be in the subthreshold region where drain current varies exponentially with S . Therefore the subthreshold swing, S, of the DTMOS is represented exactly as S DTMOS ¼ ðk B T=qÞ ln 10 whereas that of conventional bulk MOSFET is written as…”

“…This sample device was the same as that used in the previous study. 10) This device was a conventional bulk pchannel MOSFET with the respective individual n-well fabricated in a p-type silicon substrate through the VLSI Design and Education Center's chip fabrication service in Japan. Its threshold voltage (V th ) was higher than À0:7 V under conventional bulk MOSFET operation, which was not adequately adjusted for low-voltage operation.…”