[经验]

时钟速度，读取噪声和低光成像

2018-10-18 09:20:21

1335 安森美时钟噪声

比较慢。
有时你只需要减慢速度。
在我们生活的快速发展的世界中，这似乎有悖常理，但有时候你确实需要放慢速度才能使它们正确。
工匠仍然需要花时间在最高层工作，不能期望艺术家按需创作。
而且我很确定没有人希望外科医生在关键手术中匆匆忙忙。
这个想法对于电路也很重要。
虽然每个人似乎总是希望事情变得更快，但增加电子设备运行的速度也会增加与电路相关的噪音。
对于某些应用来说，降低噪音比让事情变得更快更重要。
例如，在天文摄影或科学成像等应用中考虑低光成像。
在这里，信号电平通常很低，可能需要很长的积分时间 - 长达1小时 - 以捕获图像中最微弱的部分。
并且在完成1小时曝光后，如果读取数据需要1秒或30，则无关紧要，只要较慢的读出速度有助于保持最终图像的完整性。
这就是为什么使用我们最新推出的KAF-16200图像传感器（一种专为这些类型的低光成像应用而设计的设备）以低于规定的最大值24 MHz的速度运行相机设计并不令人惊讶。
根据经验，在1MHz或更快的速度下操作的图像传感器的读取噪声与频率比的平方根成反比。
（低于1 MHz，其他噪声因素开始占主导地位。）这意味着将时钟速度从24 MHz降至1 MHz可以将读取噪声降低五倍。
当与此设备提供的同类最佳暗电流相结合时，这种类型的噪声优化设计将允许以所有1600万像素的分辨率捕获图像的最细微细节。
当然，没有什么是免费的 - 工作仍然需要在摄像机设计端完成，以确保整体系统噪音保持足够低，以便在这些低速运行时利用图像传感器提供的性能。
但是，这种缓慢，细致的工作最终能够以最高的灵敏度捕获图像。
因为有时，能够变慢是真正重要的。

以上来自于谷歌翻译

以下为原文

Slower.  Sometimes you just need to slow things down.  It may seem counterintuitive in the fast-moving world in which we live, but there are times when you really do need to slow things down in order to get them right.  Craftsmen still need to take their time to work at the highest level, and artists can’t be expected to be creative on demand.  And I’m pretty sure no one wants surgeons rushed during a critical operation.
This idea is important for electrical circuits as well.  While everyone always seems to want things to go faster, increasing the speed at which electronics run also increases the noise associated with the circuit.  And for some applications, keeping the noise down is more important than getting things to go faster.
As an example, consider low-light imaging in applications such as astrophotography or scientific imaging.  Here, signal levels are often so low that very long integration times – up to 1 hour – may be needed in order to capture the faintest parts of an image.  And after completing a 1 hour exposure, it doesn’t matter too much if readout of the data takes 1 second or 30, as long as that slower readout speed helps to preserve the integrity of the final image.

That’s why it won’t be surprising to see camera designs using our newly announced KAF-16200 image sensor – a device specifically designed for these types of low-light imaging applications – running at speeds well below the stated maximum of 24 MHz.  As a rule of thumb, the read noise of an image sensor operated around 1 MHz or faster is inversely proportional to the square root of the ratio of frequencies.  (Below 1 MHz, other noise factors begin to dominate.)  That means that dropping the clock speed from 24 MHz to 1 MHz offers the possibility of reducing read noise by up to a factor of five.  And when combined with the best-in-class dark current available from this device, this type of noise-optimized design would allow even the most subtle details of an image to be captured with all 16 megapixels of resolution.
Of course nothing comes for free – work will still need to be done on the camera design end to ensure that the overall system noise remains low enough to take advantage of the performance available from the image sensor when operated at these slow speeds.  But that type of slow, careful work is what ultimately enables the capture of images with the highest sensitivity.
Because sometimes, being able to go slower is what really matters.