Compensation for Process and Temperature Dependency in a CMOS Image Sensor

Abstract

This paper analyzes and compensates for process and temperature dependency among a (Complementary Metal Oxide Semiconductor) CMOS image sensor (CIS) array. Both the analysis and compensation are supported with experimental results on the CIS’s dark current, dark signal non-uniformity (DSNU), and conversion gain (CG). To model and to compensate for process variations, process sensors based on pixel source follower (SF)’s transconductance gm,SF have been proposed to model and to be compared against the measurement results of SF gain ASF. In addition, ASF’s thermal dependency has been analyzed in detail. To provide thermal information required for temperature compensation, six scattered bipolar junction transistor (BJT)-based temperature sensors replace six image pixels inside the array. They are measured to have an untrimmed inaccuracy within ±0.5 ⁰C. Dark signal and CG’s thermal dependencies are compensated using the on-chip temperature sensors by at least 79% and 87%, respectively.

Automotive 3.0 µm Pixel High Dynamic Range Sensor with LED Flicker Mitigation

“…Presented SF gain measurements showed reverse trend vs. temperature, earlier studies on pixel conversion and column amplifier gains showed same trend [11], then measured normalized PTF gains (DN/e) for both low (LCG) and high (HCG) conversion gains showed the similar temperature trends as depicted in Figure 18.…”

“…To understand the temperature impact from the shifting pixel parameters such as SF and PTF gains we performed measurements on five sensor sites across a wafer. Temperature dependency of the SF gain was studied before in consumer range from −20 to +80 • C [11], we extended the range to cover entire automotive range from −40 to +200 • C.…”

“…Measured LCG and HCG PTF gains reflected combined effect from the temperature dependencies of the pixel SF, floating diffusion, in-pixel capacitor node, and column amplifier. Measured pixel SF and PTF gains vs. temperature contributed to pixel output signal slope and were factored into further analysis the SF gain was studied before in consumer range from −20 to +80 °C [11], we extended the range to 2 cover entire automotive range from −40 to +200 °C.…”

1/f Noise Modelling and Characterization for CMOS Quanta Image Sensors

“…Dash lines are used to mark the noise in electrons, from which the minimum noise 0.17 e − rms at −70 • C is clearly observed. The CG is higher at low temperature, i.e., 352 µV/e − on average at −70 • C versus 340 µV/e − at 25 • C, likely due to the increase of SF gain as a result of mobility increase thus transconductance increase [18]. The increase of SF gain will reduce the Miller capacitance at the FD node due to gate-source overlap, hence the measured CG is higher at −70 • C. However, the read noise reduction at lower temperatures is not only due to increasing CG, but also SF noise reduction, since CG increases~4% but input-referred read noise decreases~15%.…”

Developing and Testing a Cooling System for CMOS in DSLR to Minimize Noise in Astronomical Image and Incorporating a Sky Quality Meter

“…As time increases, the dark current will continue to grow until each pixel is fully charged. In addition, the temperature of the CMOS sensor will also increase the dark current exponentially [35]. To overcome this, the dark current can be drastically reduced by cooling the temperature of the camera sensor.…”