Digital still and video cameras require ADCs with high 14b or more of resolution to obtain sufficient image quality after the data pass through the color processing pipeline. A columnparallel ADC in CMOS image sensors helps to enable high-speed readout of high-quality images by preventing the large wideband noise caused by high-speed analog readout circuits to be superimposed. Recently, a 6.4Mpixel low-noise CMOS image sensor with a column-parallel single-slope 12b ADC and a VGAsize wide dynamic-range CMOS image sensor with a columnparallel 12b cyclic ADC have been developed [1] [2]. The resolutions of column-parallel ADCs that have been developed to date are limited to 12b. This paper presents a CMOS image sensor integrating a 14b column-parallel cyclic ADC with on-chip digital error correction circuits. Figure 2.7.1 shows the cyclic ADC with built-in noise canceller. It consists of one amplifier, four capacitors, two comparators and several switch transistors. Cyclic ADCs have been used for wide dynamic-range CMOS imagers with the pixel pitches of 10μm or larger [2-4]. The ADC of Fig. 2.7.1 has simplified circuits and can be embedded in the column of a CMOS image sensor with a 7.5μm pixel pitch. Figure 2.7.2 shows the phase diagrams illustrating the operations of noise cancellation, sampling and amplifying for this cyclic ADC. In order to perform correlated double sampling (CDS) for pixel noise cancelling, the reset level V reset of the pixel output is sampled by capacitors C 1 and C 2 , and the signal level V signal is sampled by capacitors C 3 and C 4 . A sub-ADC is then connected to the differential input terminal to determine the most significant digit (MSD). Switching in a DAC is carried out by the MSD, and top plates of the capacitors C 1 and C 3 are connected to the DAC. After this operation, the amplifier output (the first analog residue) is given by 2(V reset -V signal ) -D 0 V R , where D 0 is the MSD which takes one of three values, -1, 0 or 1, and V R = V RP -V RN is reference voltage used in the DAC. In the sampling phase of the second cycle, the amplifier output is sampled by capacitors C 1 and C 3 , and simultaneously the second significant digit (D 1 ) is determined by the sub-ADC. In the amplification phase, the top plates of capacitors C 1 and C 3 are connected to the DAC. In this operation, the reference voltage generated by the DAC is subtracted from the 1 st residue which is multiplied by two to create a second analog residue at the amplifier output. In order to obtain 14b resolution after the digital error correction, this procedure is repeated for 15 times.In each cycle of the cyclic A/D conversion, capacitor mismatch, finite open-loop amplifier gain and offset caused by charge injection from the switches cause an error. During the A/D conversion, the errors of all the cycles are accumulated, but errors of latter cycles are less important because of the gain of two at each cycle. The resulting total error due to capacitor mismatch, finite amplifier gain and offset errors is expressed as w...
Recent advances in vision-based tactile sensation have given rise to a novel class of high-performance sensing devices that measure traction fields (i.e. distributions of 3-D force vectors) with density comparable to the biological sense of touch. While this has been-an emerging trend in robotics, it introduces diverse new possibilities for human-computer interaction as well. We describe how to apply computer vision techniques to measure the traction field applied to the surface of a silicone body, and discuss the potential of using the computed vector distribution as a rich and versatile interface for interactive desktop applications.
A distributed tactile sensor that can sense multi-axis forces and is high-densely arrayed is required in such VR applications as robotic hands and glove-like controllers in tele-existence systems. We are developing elements of a tactile sensor that can simultaneously measure pressure and shear force, and they are small enough to be arrayed densely in small areas due to MEMS process fabrication. However, the signal processing of numerous sensor elements remains a serious problem. In this paper, we studied a solution by a strategy of distributed processing and examined its effectiveness in a simulated environment.
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