Charge Modulation Device Research Articles

ＣＭＤ撮像素子を用いた広ダイナミックレンジ撮像方式

Charge-modulation-device (CMD) image sensors feature non-destructive readout and high-speed operation. By using the source-reset method in the CMD reset operations, it is possible to control the reset of the pixel-accumulated charge from outside the sensor. Making use of these features, we propose a subject-adaptive-type wide-dynamic-range imaging system that increases the dynamic range of the CMD by activating the electronic shutter only for areas having strong incident light. This prevents the sensor from becoming saturated. The advantage of this system is that there is no need to modify the conventional CMD structure to increase the dynamic range-only a simple circuit need be added outside the sensor. Experiment on this system was performed using such CMDs as line and two-dimensional sensors, and the dynamic range was increased twice as much.

A 4 M-Pixel CMD image sensor with block and skip access capability

A 4M-pixel Charge Modulation Device (CMD) image sensor with pixel size of 7.5/spl times/7.5 /spl mu/m/sup 2/ has been developed for high-resolution imaging and machine vision applications. This CMD image sensor features three scanning modes and low dark current generation. The three scanning modes include a full readout mode, a block access mode, and a skip access mode. A 4M-pixel resolution image is obtained in a single readout cycle with the full readout mode, while an arbitrary window-of-interest can be read out with the block access mode. The skip access mode reads every fourth pixel in both horizontal and vertical directions. The block and skip access modes allow real-time monitoring of a partial and rough image of the full angle of view. These scanning modes are realized by using dynamic shift registers. The sensor also has a capability of lowering the dark current generation during a long integration time by controlling the drain voltage of the CMD. The sensor has the sensitivity of 440 nA/lx and consumes 90 mW at the horizontal scanning frequency of 12 MHz in the block access mode. Measured dynamic range of 70 dB is limited by the dark current shot noise in the full readout mode.

An epitaxially-grown charge modulation device

A charge modulation device (CMD) has been fabricated in a p-type epitaxial layer grown from the buried-channel silicon region of a charge-coupled device (CCD). Construction of the CMD directly above the CCD buried-channel and over the oxidized CCD transfer gates lowers the effective sense capacitance while providing isolation of the CMD source/drain regions. Responsivity values of 28 and 66 /spl mu/V/e for feedback and no feedback conditions, respectively, were measured dynamically on test devices. Input-referred noise values of approximately four electrons r.m.s. were calculated from noise spectral density measurements assuming a low-pass filter 3 dB cutoff frequency of 5 MHz and correlated double sampling.

固体撮像とその関連技術 ４板撮像方式を用いた２０００ライン動画撮像実験装置

We have developed a 2K × 2K progressive scan color camera system. In the development, two key technologies were applied. One of the technologies enables a sensor to be operated at a high data rate. In the system, four CMD (Charge Modulation Device) chips with 1920 (H) x 1035 (V) pixel are driven at 167-M pixel/sec in progressive scan mode respectively. The other technology uses the four-sensors pickup method in which two sensors are used for green and two sensors for red and blue. The spatial offset imaging method in the vertical direction was applied to the two green sensors, thus increasing the number of vertical lines in the green channel to 2070 (twice the number of one CMD). Using these technologies, an ultra high definition camera with a data rate of 334-MHz pixel/sec has been achieved and we are sure that a vertical limiting resolution has been produced of more than 1500 TVL on a color monitor.

Carrier Reset Operation in Charge Modulation Device

The reset operation of the charge modulation device (CMD) transistor was examined by experiments and calculations. It was clarified that such conditions as high drain voltage, low reset gate voltage, short reset time or scaling down the size of the CMD transistor have a tendency to cause reset incompleteness. However, it was revealed experimentally that an ordinary bias condition for the CMD imager leads to complete reset in 50 ns reset pulse duration even if the size of the CMD transistor is scaled down to 5.0 µm×5.2 µm. This reset time is very short compared to the allowed time for the CMD reset operation of about 10 µs and 1 µs in national television system committee (NTSC) and high definition television (HDTV) format, respectively. It was also revealed by calculations that lowering the drain voltage synchronized with reset timing is very promising for rapid and complete reset operation. This method is applicable to all sizes of CMDs.

１インチ２００万画素ＣＭＤイメージセンサ

This paper presents the experimental results of a high resolution CMD (Charge Modulation Device) image sensor. This sensor features ultra-low power dissipation and a low smear level.We designed, fabricated and studied a 2M pixel CMD image sensor. A pixel size of 7.3 μm (H) ×7.6μm (V) was used to obtain a 1-in optical format HDTV image sensor. We achieved a die size of 16.6 mm (H) ×10.7mm (V), even though the clock drivers for the scanners were fabricated in the sensor chip.The smear level was-123 dB and the power dissipation was 206 mW. The saturation signal current per pixel was 28 μA at an exposure of 76 lx (Tc=5100 K, 1/60s integration). The signal had good linearity of photoconversion characteristics. Furthermore, the image lag was lower than the detectable limit (0.1% of the saturation signal).

Analysis of operational speed and scaling down the pixel size of a charge modulation device (CMD) image sensor

In a previous paper, the authors (ibid., vol.38, pp.989-998, May 1991) clarified the operational mechanism of a charge modulation device (CMD) image sensor and confirmed that numerical calculations using the transistor analysis program for imagers calculating non-steady-state equations (TRINE) predicted the actual performance of a CMD imager within a 20% discrepancy. Following these results, the scaling-down of device dimensions and the inherent operational speed are estimated using TRINE in order to realize a future high-resolution CMD image sensor. The analysis shows that a device size of 5.0 mu m (H)*5.2 mu m (V) is attainable without degrading the performance of the 10.2 mu m (H)*10.4 mu m (V) CMD imager and that the operational speed of a CMD is fast enough for a high-definition TV (HDTV) application which requires a scan rate of several tens of nanoseconds. >

The operation mechanism of a charge modulation device (CMD) image sensor

The operational mechanism of the charge modulation device (CMD) as an image sensor is presented. A newly developed device simulator, the transistor analysis program for imagers calculating non-steady-state equations (TRINE) is used in this analysis. Comparison of the calculated results with measured data shows that the model predictions are consistent with measured electrical and optical characteristics within a range of 20%. The operational mechanism has been clarified, and the accuracy of the method proves that it is effective in quantitative device design. The discretization scheme of the cylindrical coordinate system used is also shown.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A small pixel CMD image sensor

A charge modulation device (CMD) imager with pixel dimensions of 7.3 mu m(H)*7.6 mu m(V) was designed, fabricated, and examined. These pixel dimensions are suitable for an HDTV imager with a 1-in image format. The optical aperture ratio is 34%. The effective number of pixels in the imager is 660 horizontal and 492 vertical. The saturation signal current is 17 mu A/pixel at an exposure of 1 lx-s with good linearity of photoconversion characteristics. The peak of its spectral response occurs at a wavelength of 575 nm. The blooming suppression ratio of the CMD was measured to be -122 dB. The sensor produces a high-quality image with no degradation in spatial resolution and no image lag. These features show that the CMD imager is eminently suitable for a further high-resolution imager sensor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>