Types Of Camera Sensor --- 相機(jī)傳感器的類型
https://www.photometrics.com/learn/camera-basics/types-of-camera-sensor
Introduction
Quantitative scientific cameras are vital for sensitive, fast imaging of a variety of samples for a variety of applications. Camera technologies have advanced over time, from the earliest cameras to truly modern camera technologies, which can push the envelope of what is possible in scientific imaging and allow us to see the previously unseen.
The heart of the camera is the sensor, and the steps involved in generating an image from photons to electrons to grey levels. For information on how an image is made, see our article of the same name. This article discusses the different camera sensor types and their specifications, including:
- Charge-coupled device (CCD)電荷耦合器件
- Electron-multiplying charge-coupled device (EMCCD)電子倍增電荷耦合器件
- Complementary metal-oxide-semiconductor (CMOS)互補(bǔ)金屬氧化物半導(dǎo)體
- Back-illuminated CMOS背照式CMOS
This order also shows the chronological order of the introduction of these sensor types, we will go through these one at a time, in a journey through the history of scientific imaging.
Sensor Fundamentals
The first step for a sensor is the conversion of photons of light into electrons (known as photoelectrons). The efficiency of this conversion is known as the quantum efficiency (QE) and is shown as a percentage.
傳感器的第一步是將光的光子轉(zhuǎn)換為電子（稱為光電子）。這種轉(zhuǎn)換的效率稱為量子效率 （QE），以百分比表示。
All the sensor types discussed here operate based on the fact that all electrons have a negative charge (the electron symbol being e–). This means that electrons can be attracted using a positive voltage, granting the ability to move electrons around a sensor by applying a voltage to certain areas of the sensor, as seen in Figure 1.
這里討論的所有傳感器類型都基于所有電子都帶負(fù)電荷的事實(shí)來工作（電子符號是 e – ）。這意味著可以使用正電壓吸引電子蔫缸，從而通過向傳感器的某些區(qū)域施加電壓來使電子在傳感器周圍移動士八，如圖 1 所示茄袖。
Figure 1: How electron charge is transferred from pixel to pixel across a sensor. Photons (black arrows) hit a pixel (blue squares) and are converted into electrons (e–) and are stored in a pixel well (yellow). These electrons can be transferred to another pixel using a positive voltage (orange), and moved anywhere on a sensor, pixel by pixel. 圖 1：電子電荷如何在傳感器上從一個像素傳遞到另一個像素访雪。光子（黑色箭頭）擊中像素（藍(lán)色方塊）并轉(zhuǎn)化為電子（e – ）并存儲在像素井（黃色）中。這些電子可以使用正電壓（橙色）轉(zhuǎn)移到另一個像素遗嗽，并逐個像素地移動到傳感器上的任何位置粘我。【正電荷吸引電子媳谁？】
In this manner, electrons can be moved anywhere on a sensor, and are typically moved to an area where they can be amplified and converted into a digital signal, in order to be displayed as an image. However, this process occurs differently in each type of camera sensor.
通過這種方式涂滴，電子可以移動到傳感器上的任何位置，并且通常被移動到可以放大并轉(zhuǎn)換為數(shù)字信號的區(qū)域晴音，以便顯示為圖像柔纵。但是，此過程在每種類型的相機(jī)傳感器中發(fā)生的情況不同锤躁。
CCD
CCDs were the first digital cameras, being available since the 1970s for scientific imaging. CCD have enjoyed active use for a number of decades and were well suited to high-light applications such as cell documentation or imaging fixed samples. However, this technology was lacking in terms of sensitivity and speed, limiting the available samples that could be imaged at acceptable levels. CCD 是第一臺數(shù)碼相機(jī)搁料，自 1970 年代以來一直可用于科學(xué)成像。CCD幾十年來一直被廣泛使用系羞，非常適合高光應(yīng)用郭计，如細(xì)胞記錄或固定樣品成像。然而椒振，該技術(shù)在靈敏度和速度方面有所欠缺昭伸，限制了可以在可接受水平下成像的可用樣品。
CCD Fundamentals
In a CCD, after exposure to light and conversion of photons to photoelectrons, the electrons are moved down the sensor row by row until they reach an area that isn’t exposed to light, the readout register. Once moved into the readout register, photoelectrons are moved off one by one into the output node. In this node they are amplified into a readable voltage, converted into a digital grey level using the analogue to digital converter (ADC) and sent to the computer via the imaging software. 在CCD中澎迎，在暴露于光并將光子轉(zhuǎn)換為光電子后庐杨，電子在傳感器上逐行向下移動，直到它們到達(dá)未暴露在光下的區(qū)域夹供，即讀出寄存器灵份。一旦進(jìn)入讀出寄存器，光電子就會一個接一個地移動到輸出節(jié)點(diǎn)中哮洽。在該節(jié)點(diǎn)中填渠，它們被放大為可讀電壓，使用模數(shù)轉(zhuǎn)換器（ADC）轉(zhuǎn)換為數(shù)字灰度電平鸟辅，并通過成像軟件發(fā)送到計(jì)算機(jī)氛什。
Figure 2: How a CCD sensor works. Photons hit a pixel and are converted to electrons, which are then shuttled down the sensor to the readout register, and then to the output node, where they are converted to a voltage, then grey levels, and then displayed with a PC. 圖 2：CCD 傳感器的工作原理。光子撞擊一個像素并被轉(zhuǎn)換為電子匪凉，然后電子被沿著傳感器傳送到讀出寄存器屉更，然后到輸出節(jié)點(diǎn)，在那里它們被轉(zhuǎn)換為電壓洒缀，然后是灰度電平，然后用PC顯示。
The number of electrons is linearly proportional to the number of photons, allowing the camera to be quantitative. The design seen in Fig.2 is known as a full-frame CCD sensor, but there are other designs known as frame-transfer CCD and interline-transfer CCD that are shown in Fig.3. 電子數(shù)與光子數(shù)成線性正比树绩，使相機(jī)能夠定量萨脑。圖 2 中的設(shè)計(jì)稱為全畫幅 CCD 傳感器，但還有其他設(shè)計(jì)稱為幀傳輸 CCD 和行間傳輸 CCD饺饭，如圖 3 所示渤早。
這到底是個俯視圖還是側(cè)視圖？瘫俊！根據(jù)后面太陽圖片鹊杖，應(yīng)該是俯視圖
Figure 3: Different types of CCD sensor. The full-frame sensor is also displayed in Fig.2. Grey areas are masked and not exposed to light. The frame-transfer sensor has an active image array (white) and a masked storage array (grey), while the interline-transfer sensor has a portion of each pixel masked (grey). 圖 3：不同類型的 CCD 傳感器。全畫幅傳感器也如圖 2 所示扛芽÷畋停灰色區(qū)域被遮蓋，不暴露在光線下川尖。幀傳輸傳感器具有活動圖像陣列（白色）和屏蔽存儲陣列（灰色）登下，而行間傳輸傳感器具有每個像素的一部分屏蔽（灰色）。
In a frame-transfer CCD the sensor is divided into two: the image array (where light from the sample hits the sensor) and the storage array (where signal is temporarily stored before readout). The storage array is not exposed to light, so when electrons are moved to this array, a second image can be exposed on the image array while the first image is processed from the storage array. The advantage is that a frame-transfer sensor can operate at greater speeds than a full-frame sensor, but the sensor design is more complex and requires a larger sensor (to accommodate the storage array), or the sensor is smaller as a portion is made into a storage array. 在幀傳輸CCD中叮喳，傳感器分為兩個：圖像陣列（來自樣品的光照射到傳感器）和存儲陣列（在讀出前臨時存儲信號）被芳。存儲陣列不會暴露在光線下，因此當(dāng)電子移動到該陣列時馍悟，可以在圖像陣列上曝光第二個圖像畔濒，同時從存儲陣列處理第一個圖像。優(yōu)點(diǎn)是幀傳輸傳感器可以比全幀傳感器以更高的速度運(yùn)行锣咒，但傳感器設(shè)計(jì)更復(fù)雜侵状，需要更大的傳感器（以容納存儲陣列），或者傳感器更小宠哄，因?yàn)橐徊糠直恢瞥纱鎯﹃嚵小?/p>
For the interline-transfer CCD, a portion of each pixel is masked and not exposed to light. Upon exposure, the electron signal is shifted into this masked portion, and then sent to the readout register as normal. Similarly to the frame-transfer sensor, this helps increase the speed, as the exposed area can generate a new image while the original image is processed. However, each pixel in this sensor is smaller (as a portion is masked), and this decreases the sensitivity as fewer photons can be detected by smaller pixels. These sensors often come paired with microlenses to better direct light and improve the QE. 對于行間傳輸CCD壹将，每個像素的一部分被遮蔽，不暴露在光線下毛嫉。曝光后诽俯，電子信號被轉(zhuǎn)移到這個掩蔽部分，然后像往常一樣發(fā)送到讀出寄存器承粤。與幀傳輸傳感器類似暴区，這有助于提高速度，因?yàn)樵谔幚碓紙D像時辛臊，曝光區(qū)域可以生成新圖像仙粱。然而，該傳感器中的每個像素都較谐菇ⅰ（因?yàn)橐徊糠直徽诒危┓ジ睿@會降低靈敏度候味，因?yàn)檩^小的像素可以檢測到的光子更少。這些傳感器通常與微透鏡配對隔心，以更好地引導(dǎo)光線并改善 QE白群。
CCD Limitations
The main issues with CCDs are their lack of speed and sensitivity, making it a challenge to perform low-light imaging or to capture dynamic moving samples.
The lack of speed is due to several factors: CCD的主要問題是缺乏速度和靈敏度，這使得執(zhí)行低光成像或捕獲動態(tài)移動樣品成為一項(xiàng)挑戰(zhàn)硬霍。
- There is only one output node per sensor. This means that millions of pixels of signal have to be shuttled through one node, creating a bottleneck and slowing the camera. 每個傳感器只有一個輸出節(jié)點(diǎn)帜慢。這意味著數(shù)百萬像素的信號必須通過一個節(jié)點(diǎn)傳輸，從而造成瓶頸并減慢相機(jī)的速度唯卖。
- If electrons are moved too quickly, it introduces error and read noise, so most CCDs elect to move electrons slower than maximum speed to attempt to reduce noise. 如果電子移動得太快粱玲，就會引入誤差和讀取噪聲，因此大多數(shù)CCD選擇以低于最大速度的速度移動電子拜轨，以試圖降低噪聲抽减。
- The whole sensor needs to be cleared of the electron signal before the next frame can be exposed 在下一幀曝光之前，需要清除整個傳感器的電子信號
Essentially, there are very few data readout channels for a CCD, meaning the data processing is slowed. Most CCDs operate at between 1-20 frames per second, as a CCD is a serial device and can only read the electron charge packets one at a time. Imagine a bucket brigade, where electrons can only be passed from area to area one at a time, or a theatre with only one exit but several million seats. 從本質(zhì)上講撩轰，CCD的數(shù)據(jù)讀出通道很少胯甩，這意味著數(shù)據(jù)處理速度會變慢。大多數(shù) CCD 以每秒 1-20 幀的速度運(yùn)行堪嫂，因?yàn)?CCD 是一種串行設(shè)備偎箫，一次只能讀取一個電子電荷包。想象一下皆串，一個水桶大隊(duì)淹办，電子一次只能從一個區(qū)域傳遞到另一個區(qū)域，或者一個只有一個出口但有幾百萬個座位的劇院恶复。
In addition, CCDs have a small full-well capacity, meaning that the number of electrons that can be stored in each pixel is limited. If a pixel can only store 200 electrons, receiving a signal of >200 electrons leads to saturation, where a pixel becomes full and displayed the brightest signal, and blooming, where the pixel overflows and the excess signal is smeared down the sensor as the electrons are moved to the readout register. 此外怜森，CCD的滿阱容量很小，這意味著每個像素中可以存儲的電子數(shù)量是有限的谤牡。如果一個像素只能存儲 200 個電子副硅，則接收 >200 個電子的信號會導(dǎo)致飽和，即像素變得飽滿并顯示最亮的信號翅萤，以及光暈恐疲，即像素溢出，多余的信號在電子移動到讀出寄存器時涂抹在傳感器上套么。
In extreme cases (such as daylight illumination of a scientific camera), there is a charge overload in the output node, causing the output amplification chain to collapse, resulting in a zero (completely dark) image. 在極端情況下（例如科學(xué)相機(jī)的日光照明）培己，輸出節(jié)點(diǎn)中存在電荷過載，導(dǎo)致輸出放大鏈崩潰胚泌，從而產(chǎn)生零（完全黑暗）的圖像省咨。
Figure 4: Examples of blooming caused by saturation of a CCD sensor pixel. Left) Picture of a sunset. The sun is so bright in the image that there is blooming on the sun itself, leaking into the surrounding pixels, and a vertical smear across the whole image. Right) A similar situation with the blooming and smear labeled. 圖 4：CCD 傳感器像素飽和引起的光暈示例。左）日落的圖片玷室。太陽在圖像中是如此明亮零蓉，以至于太陽本身就會開花笤受，泄漏到周圍的像素中，并且整個圖像上有垂直的涂抹壁公。右）類似的情況感论，帶有開花和涂抹標(biāo)記。
CCD pixels are also typically quite small (such as ~4 μm) meaning that while these sensors can achieve a high resolution, they lack sensitivity, as a larger pixel can collect more photons. This limits signal collection and is compounded by the limited QE of front-illuminated CCDs, which often only reaches 75% at maximum. CCD像素通常也非常形刹帷（例如~4μm），這意味著雖然這些傳感器可以實(shí)現(xiàn)高分辨率快耿，但它們?nèi)狈`敏度囊陡，因?yàn)檩^大的像素可以收集更多的光子。這限制了信號收集掀亥，并且由于前照式CCD的QE有限而變得更加復(fù)雜撞反，通常最大只能達(dá)到75%。
Finally, CCD sensors are typically quite small, with an 11-16 mm diagonal, which limits the field of view that can be displayed on the camera and means that not all of the information from the microscope can be captured by the camera.
最后搪花，CCD傳感器通常非常小遏片，對角線為11-16毫米，這限制了相機(jī)上可以顯示的視野撮竿，并意味著相機(jī)無法捕獲顯微鏡的所有信息吮便。
Overall, while CCDs were the first digital cameras, for scientific imaging purposes in the modern day they are lacking in speed, sensitivity and field of view.
EMCCD
EMCCDs first emerged onto the scientific imaging scene in 2000 with the Cascade 650 from Photometrics. EMCCDs offered faster and more sensitive imaging then CCDs, useful for low-light imaging or even photon counting.
EMCCDs achieved this in a number of ways. The cameras are back-illuminated (increasing the QE to ~90%) and have very large pixels (16-24 μm), both of which greatly increase the sensitivity. The most significant addition, however, is the EM in EMCCD: electron multiplication. EMCCD以多種方式實(shí)現(xiàn)了這一點(diǎn)。相機(jī)采用背照式（將QE提高到~90%）幢踏，并具有非常大的像素（16-24μm）髓需，這兩者都大大提高了靈敏度。然而房蝉，最重要的補(bǔ)充是EMCCD中的EM：電子倍增僚匆。
EMCCD Fundamentals
EMCCDs work in a very similar way to frame-transfer CCDs, where electrons move from the image array to the masked array, then onto the readout register. At this point the main difference emerges: the EM Gain register. EMCCDs use a process called impact ionisation to force extra electrons out of the silicon sensor, therefore multiplying the signal. This EM process occurs step-by-step, meaning users can choose a value between 1-1000 and have their signal be multiplied that many times in the EM Gain register. If an EMCCD detects a signal of 5 electrons and has an EM Gain set to 200, the final signal that goes into the output node will be 1000 electrons. This allows EMCCDs to detect extremely small signals, as they can be multiplied up above the noise floor as many times as a user desires. EMCCD的工作方式與幀傳輸CCD非常相似，其中電子從圖像陣列移動到掩膜陣列搭幻，然后移動到讀出寄存器上咧擂。此時，主要區(qū)別就出現(xiàn)了：EM增益寄存器檀蹋。EMCCD使用一種稱為沖擊電離的過程來迫使額外的電子從硅傳感器中排出松申，從而使信號成倍增加。此EM過程是逐步進(jìn)行的续扔，這意味著用戶可以在1-1000之間選擇一個值攻臀，并在EM增益寄存器中將其信號乘以多次。如果EMCCD檢測到5個電子的信號并將EM增益設(shè)置為200纱昧，則進(jìn)入輸出節(jié)點(diǎn)的最終信號將是1000個電子刨啸。這使得EMCCD能夠檢測到極小的信號，因?yàn)樗鼈兛梢愿鶕?jù)用戶的需要在噪聲基底以上多次增加识脆。
Figure 5: How an EMCCD sensor works. Photons hit a pixel and are converted to electrons, which are then shuttled down the sensor to the readout register. From here they are amplified using the EM Gain register, then sent to the output node, where they are converted to a voltage, then grey levels, and then displayed with a PC. 圖 5：EMCCD 傳感器的工作原理设联。光子擊中一個像素并轉(zhuǎn)化為電子善已，然后電子沿著傳感器向下穿梭到讀出寄存器。從這里開始离例，它們使用EM增益寄存器被放大换团，然后發(fā)送到輸出節(jié)點(diǎn)，在那里它們被轉(zhuǎn)換為電壓宫蛆，然后是灰度電平艘包，然后用PC顯示。
This combination of large pixels, back-illumination and electron multiplication makes EMCCDs extremely sensitive, far more so than CCDs. 這種大像素耀盗、背照和電子倍增的結(jié)合使EMCCD非常靈敏想虎，遠(yuǎn)遠(yuǎn)超過CCD。
EMCCDs are also faster than CCDs. In CCDs, electrons are moved around the sensor at speeds well below the maximum possible speed, because the faster the electrons are shuttled about, the greater the read noise. Read noise is a fixed +/- value on every signal, if a CCD has a read noise of ±5 electrons and detects a signal of 10 electrons, it could be read out at anywhere between 5-15 electrons depending on the read noise. This has a big impact on sensitivity and speed, as CCDs move electrons slower in order to reduce read noise. However, with an EMCCD you can just multiply your signal up until the read noise has a negligible effect. This means that EMCCDs can move signal around at maximum speed, resulting in huge read noise values from 60-80 electrons, but signals are often multiplied by hundreds of times, meaning that the read noise impact is lessened. In this manner, EMCCDs can operate at much higher speeds than CCDs, achieving around 30-100 fps across the full-frame. This is only possible due to the EM Gain aspect of EMCCDs. EMCCD也比CCD更快叛拷。在CCD中舌厨，電子以遠(yuǎn)低于最大可能速度的速度在傳感器周圍移動，因?yàn)殡娮哟┧蟮迷娇旆揶保x取噪聲就越大裙椭。讀取噪聲是每個信號的固定+/-值，如果CCD的讀取噪聲為±5個電子并檢測到10個電子的信號署浩，則可以根據(jù)讀取噪聲在5-15個電子之間的任何位置讀出揉燃。這對靈敏度和速度有很大影響，因?yàn)镃CD為了降低讀取噪聲而移動電子的速度較慢瑰抵。但是你雌，使用EMCCD，您只需將信號相乘二汛，直到讀取噪聲的影響可以忽略不計(jì)婿崭。這意味著EMCCD可以以最大速度移動信號运授，從而產(chǎn)生來自60-80個電子的巨大讀取噪聲值扫沼，但信號通常會乘以數(shù)百倍轻猖，這意味著讀取噪聲的影響會降低只泼。通過這種方式魄懂，EMCCD可以以比CCD高得多的速度運(yùn)行溶耘，在全畫幅上實(shí)現(xiàn)約30-100fps谐区。這只有在EMCCD的EM增益方面才有可能叉瘩【顾危【提高電子速度導(dǎo)致提高噪聲提完，但是信號倍乘遠(yuǎn)大于噪音】
EMCCD Limitations
Despite the advantages of electron multiplication, it introduces a lot of complexity to the camera and leads to several major downsides. The main technological issues are EM Gain Decay, EM Gain Stability and Excess Noise Factor. 盡管電子倍增具有優(yōu)點(diǎn)，但它給相機(jī)帶來了很多復(fù)雜性丘侠，并導(dǎo)致了幾個主要缺點(diǎn)徒欣。主要技術(shù)問題是電磁增益衰減、電磁增益穩(wěn)定性和過量噪聲因數(shù)蜗字。
EM gain decay or ageing is a phenomenon that is not fully understood, but essentially involves charge building up in the silicon sensor between the EM electrode and photodetector. This build-up of charge reduces the effect of EM gain, hence EM gain decay. The greater the initial signal intensity and the higher the EM gain, the faster the EM gain will decay. Using an EM gain of 1000x on a large signal would quickly result in EM gain decay. This results in the EM gain not being the same each time, leading to a lack of reproducibility in experiments, limiting the usefulness of the camera as a quantitative imaging tool. EMCCDs essentially have limited lifespans and require regular calibration, leading to these cameras needing to be used in a certain way, limiting the EM gain that can be used in an experiment without damaging the camera. When a camera has been purchased and will be used daily in a research lab, it can be disappointing to learn that the camera will become less and less reliable over time. EM增益衰減或老化是一種尚不完全了解的現(xiàn)象打肝，但本質(zhì)上涉及EM電極和光電探測器之間的硅傳感器中的電荷積聚脂新。這種電荷的積累降低了EM增益的影響，從而降低了EM增益衰減粗梭。初始信號強(qiáng)度越大争便，EM增益越高，EM增益衰減得越快断医。在大信號上使用1000倍的EM增益會很快導(dǎo)致EM增益衰減滞乙。這導(dǎo)致每次的EM增益都不相同，導(dǎo)致實(shí)驗(yàn)中缺乏可重復(fù)性鉴嗤，限制了相機(jī)作為定量成像工具的實(shí)用性酷宵。EMCCD基本上具有有限的使用壽命，需要定期校準(zhǔn)躬窜，導(dǎo)致這些相機(jī)需要以某種方式使用，從而限制了可以在實(shí)驗(yàn)中使用的EM增益炕置，而不會損壞相機(jī)荣挨。當(dāng)購買了相機(jī)并將在研究實(shí)驗(yàn)室中每天使用時，得知相機(jī)會隨著時間的推移變得越來越不可靠朴摊，這可能會令人失望默垄。
In addition, the EM gain process itself is not stable, different fluctuations can occur. One such example is EM gain being temperature-dependent, in order for EMCCDs to have reliable EM gain they typically operate at temperates from -60 oC to -80 oC, meaning they require extensive forced-air or liquid cooling. This all adds to the camera complexity and cost, especially if a liquid cooling rig needs to be installed with the camera. 此外，EM增益過程本身并不穩(wěn)定甚纲，可能會發(fā)生不同的波動口锭。一個這樣的例子是EM增益與溫度有關(guān)，為了使EMCCD具有可靠的EM增益介杆，它們通常在-60oC至-80oC的溫度下工作鹃操，這意味著它們需要大量的強(qiáng)制空氣或液體冷卻。這一切都增加了相機(jī)的復(fù)雜性和成本春哨，特別是當(dāng)相機(jī)需要安裝液體冷卻裝置時荆隘。
While an EMCCD can multiply signal far above the reaches of read noise, these cameras are subject to other sources of noise, unique to EMCCDs. The number of photons a camera detects is not the same every second, as photons typically fall like rain rather than arrive at the sensor in regimented rows. This disparity between measurements is called photon shot noise. Photon shot noise and other sources of noise all exist in the signal as soon as it arrives on the sensor, and these noise sources are all multiplied up along with the signal, resulting in the Excess Noise Factor. The combination of random photon arrival and random EM multiplication leads to extra sources of error and noise, with all sources of noise (predominantly photon shot noise) being multiplied by a factor of 1.4x. While an EMCCD may eliminate read noise, it introduces its own sources of noise, impacting the signal-to-noise ratio and the ability of the camera to be sensitive. 雖然EMCCD可以增加遠(yuǎn)高于讀取噪聲范圍的信號，但這些相機(jī)會受到EMCCD特有的其他噪聲源的影響赴背。相機(jī)每秒檢測到的光子數(shù)量并不相同椰拒，因?yàn)楣庾油ǔＯ裼暌粯勇湎拢皇浅膳诺竭_(dá)傳感器凰荚。測量值之間的這種差異稱為光子散粒噪聲燃观。光子散粒噪聲和其他噪聲源一旦到達(dá)傳感器就存在于信號中，并且這些噪聲源都隨著信號相乘便瑟，從而產(chǎn)生過量噪聲因子缆毁。隨機(jī)光子到達(dá)和隨機(jī)電磁倍增的組合會導(dǎo)致額外的誤差和噪聲源，所有噪聲源（主要是光子散粒噪聲）都乘以 1.4 倍胳徽。雖然EMCCD可以消除讀取噪聲积锅，但它會引入自己的噪聲源爽彤，從而影響信噪比和相機(jī)的靈敏度。
Finally, the large pixels of an EMCCD lead to these cameras having a lower resolution than CCDs; EMCCDs have a small field of view due to their small sensors; and even today (20 years later) EMCCDs are still the most expensive format of scientific camera. 最后缚陷，EMCCD的大像素導(dǎo)致這些相機(jī)的分辨率低于CCD;EMCCD由于傳感器小适篙，視野小;即使在今天（20 年后），EMCCD 仍然是最昂貴的科學(xué)相機(jī)格式箫爷。
While EMCCDs greatly improved on the speed and sensitivity of CCDs, they brought their own issues and continued to limit the amount of information that could be obtained from the microscope.
CMOS
While MOS and CMOS technology has existed since before CCD (~1950’s), only in 2009 did CMOS cameras become quantitative enough to be sufficient for scientific imaging, hence why CMOS cameras for science can be referred to as scientific CMOS or sCMOS. 雖然MOS和CMOS技術(shù)早在CCD之前就已經(jīng)存在（~1950年代）嚷节，但直到2009年，CMOS相機(jī)才變得足夠量化虎锚，足以進(jìn)行科學(xué)成像硫痰，因此用于科學(xué)的CMOS相機(jī)可以被稱為科學(xué)CMOS或sCMOS。
CMOS technology is different to CCD and EMCCD, the main factor being parallelization, CMOS sensors operate in parallel and allow for much higher speeds. CMOS技術(shù)與CCD和EMCCD不同窜护，主要因素是并行化效斑，CMOS傳感器并行運(yùn)行并允許更高的速度。
CMOS Fundamentals
In a CMOS sensor there are miniaturized electronics on every single pixel, namely a capacitor and amplifier. This means that a photon is converted to an electron by the pixel, and then the electron is immediately converted to a readable voltage while still on the pixel. In addition, there is an ADC for every single column, meaning that each ADC has far less data to read out than a CCD/EMCCD ADC, which has to read out the entire sensor. This combination allows CMOS sensors to work in parallel, and process data much faster than CCD/EMCCD technologies. By moving electrons much slower than the potential max speed, CMOS sensors also have a much lower read noise than CCD/EMCCD, allowing them to perform low-light imaging and work with weak fluorescence or live cells.
在CMOS傳感器中柱徙，每個像素上都有微型電子元件缓屠，即電容器和放大器。這意味著光子被像素轉(zhuǎn)換為電子护侮，然后電子在像素上立即轉(zhuǎn)換為可讀電壓敌完。此外，每列都有一個ADC羊初，這意味著每個ADC要讀出的數(shù)據(jù)比CCD/EMCCD ADC少得多滨溉，后者必須讀出整個傳感器。這種組合使CMOS傳感器能夠并行工作长赞，并且處理數(shù)據(jù)的速度比CCD/EMCCD技術(shù)快得多晦攒。CMOS傳感器的電子移動速度遠(yuǎn)低于潛在最大速度，因此讀取噪聲也比CCD/EMCCD低得多涧卵，從而可以進(jìn)行弱光成像勤家，并與弱熒光或活細(xì)胞一起工作。
Figure 6: How a CMOS sensor works. Photons hit a pixel and are converted to electrons, and then converted to voltage on the pixel. Each column is then read out separately by individual ADCs, and then displayed with a PC. 圖 6：CMOS 傳感器的工作原理柳恐。光子撞擊像素并轉(zhuǎn)化為電子伐脖，然后轉(zhuǎn)換為像素上的電壓。然后乐设，每列由單獨(dú)的ADC單獨(dú)讀出讼庇，然后用PC顯示。
CMOS sensors have also been adopted by the commercial imaging industry, meaning that nearly every smartphone camera, digital camera, or imaging device uses a CMOS sensor. This makes these sensors easier and cheaper to manufacture, allowing sCMOS cameras to feature large sensors and have much larger fields of view than CCD/EMCCD, to the point where some sCMOS cameras can capture all the information from the microscope. CMOS傳感器也被商業(yè)成像行業(yè)采用近尚，這意味著幾乎每個智能手機(jī)相機(jī)蠕啄、數(shù)碼相機(jī)或成像設(shè)備都使用CMOS傳感器。這使得這些傳感器的制造更容易、更便宜歼跟，使sCMOS相機(jī)能夠配備大型傳感器和媳，并且具有比CCD/EMCCD大得多的視場，以至于一些sCMOS相機(jī)可以從顯微鏡捕獲所有信息哈街。
In addition, CMOS sensors had a large full well capacity, meaning they had a large dynamic range and could simultaneously image dark signals and bright signals, not subject to saturation or blooming like with a CCD. 此外留瞳，CMOS傳感器具有較大的滿阱容量，這意味著它們具有較大的動態(tài)范圍骚秦，可以同時成像暗信號和亮信號她倘，而不會像CCD那樣受到飽和或光暈的影響。
Early CMOS Limitations
Early sCMOS cameras featured much higher speeds and larger fields of view than CCD/EMCCD, and with a range of pixel sizes, there were CMOS cameras that imaged at very high resolution, especially compared to EMCCD. However, the large pixel and electron multiplication of EMCCDs meant that early sCMOS cameras couldn’t rival EMCCD when it came to sensitivity. When it came to extreme low-light imaging or the need for sensitivity, EMCCD still had the edge. 早期的sCMOS相機(jī)比CCD/EMCCD具有更高的速度和更大的視場作箍，并且具有一系列像素尺寸硬梁，因此CMOS相機(jī)可以以非常高的分辨率成像，尤其是與EMCCD相比胞得。然而荧止，EMCCD的大像素和電子倍增意味著早期的sCMOS相機(jī)在靈敏度方面無法與EMCCD相媲美。當(dāng)涉及到極低光成像或需要靈敏度時阶剑，EMCCD仍然具有優(yōu)勢罩息。
Figure 7: Camera sensitivity. While early CMOS was far more sensitive than CCDs due to lower read noise, early CMOS couldn’t compete with EMCCD and the near elimination of read noise. 7：相機(jī)靈敏度。雖然早期的CMOS由于讀取噪聲較低而比CCD更靈敏个扰，但早期的CMOS無法與EMCCD競爭，并且?guī)缀蹩梢韵x取噪聲葱色。
Figure 8: Split sensor sCMOS patterns and artifacts. While early CMOS was far more sensitive than CCDs due to lower read noise, early CMOS couldn’t compete with EMCCD and the near elimination of read noise. 圖 8：分離式傳感器 sCMOS 圖案和偽影递宅。雖然早期的CMOS由于讀取噪聲較低而比CCD更靈敏，但早期的CMOS無法與EMCCD競爭苍狰，并且?guī)缀蹩梢韵x取噪聲办龄。
In Fig.8 we can see the bias of a split sensor camera, showing a horizontal line separating the two halves of the sensor, along with the other horizontal scrolling lines. This is due to each sensor half never being exactly the same due to noise and fluctuations. This effect is exacerbated when 100 image frames are averaged, as seen in the lower image. Here the sensor split is also clear, as are vertical columns across the image. This is fixed pattern column noise and is again due to the ADC pairs of the sensor. This noise can interfere with signal in low-light conditions. 在圖 8 中，我們可以看到分體式傳感器相機(jī)的偏置淋昭，顯示了一條水平線將傳感器的兩半分開俐填，以及其他水平滾動線。這是因?yàn)橛捎谠肼暫筒▌酉韬觯總€傳感器的一半永遠(yuǎn)不會完全相同英融。當(dāng)平均 100 個圖像幀時，這種效果會加劇歇式，如下圖所示驶悟。在這里，傳感器的分裂也很清晰材失，圖像上的垂直列也是如此痕鳍。這是固定模式的列噪聲，同樣是由傳感器的ADC對引起的。這種噪聲會干擾弱光條件下的信號笼呆。
These early sCMOS sensors were front-illuminated and therefore had a limited QE (70-80%), further impacting their sensitivity. 這些早期的sCMOS傳感器是前照式的熊响，因此QE有限（70-80%），進(jìn)一步影響了它們的靈敏度诗赌。
Some early sCMOS, in an effort to run at a higher speed, featured a split sensor, where each half of the sCMOS sensor had its own set of ADCs and the camera image at speeds up to 100 fps. However, this split caused patterns and artifacts in the camera bias, which would be clearly visible in low-light conditions and would interfere with the signal, as seen in Figure 8. 為了以更高的速度運(yùn)行汗茄，一些早期的sCMOS采用了分離式傳感器，其中sCMOS傳感器的每一半都有自己的一組ADC境肾，并且相機(jī)圖像的速度高達(dá)100 fps剔难。然而，這種分裂導(dǎo)致了相機(jī)偏置中的圖案和偽影奥喻，在低光條件下清晰可見偶宫，并且會干擾信號，如圖8所示环鲤。
This combination of front-illumination, split sensors, patterns/artifacts, and smaller pixels all led to early sCMOS lacking in sensitivity. 這種前照式纯趋、分離式傳感器、圖案/偽影和較小像素的組合都導(dǎo)致早期的sCMOS缺乏靈敏度冷离。
Back-Illuminated sCMOS
In 2016 Photometrics released the first back-illuminated sCMOS camera, the Prime 95B. Back-illuminated (BI) sCMOS cameras greatly improve on sensitivity compared to early front-illuminated sCMOS, while retaining all the other CMOS advantages such as high speed, large field of view. The combination of a much higher QE due to back-illuminated (up to 95%, hence the name of the Prime 95B), the single sensor (no split), more varied pixel sizes, and a cleaner background, BI sCMOS is the all-in-one imaging solution. 2016年吵冒，Photometrics發(fā)布了第一款背照式sCMOS相機(jī)Prime 95B。與早期的前照式sCMOS相比西剥，背照式（BI） sCMOS相機(jī)的靈敏度大大提高痹栖，同時保留了所有其他CMOS優(yōu)勢，如高速瞭空、大視場揪阿。BI sCMOS具有背照式（高達(dá)95%，因此得名Prime 95B）咆畏、單傳感器（無分割）南捂、更多樣化的像素尺寸和更清晰的背景，因此具有更高的QE旧找，是一體化成像解決方案溺健。
BI sCMOS Fundamentals
Back-illumination allows for a large increase in camera QE across wavelengths from UV to IR, due to the way that light can access the camera sensor. Figure 9 highlights the differences between a front-illuminated and back-illuminated camera sensor. 背照允許在從紫外到紅外的波長范圍內(nèi)大幅增加相機(jī)QE，因?yàn)楣饩€可以進(jìn)入相機(jī)傳感器钮蛛。圖 9 突出顯示了前照式和背照式攝像頭傳感器之間的差異鞭缭。
Figure 9: Front-illumination vs back-illumination for camera sensors. Front-illuminated sensors (CCDs and early sCMOS) have the light come in from the front, where it passes through microlenses, wiring, electronics, and more before reaching the photodetector. Back-illuminated sensors (EMCCD and BI sCMOS) have a flipped sensor where the light comes in from the ‘back’, immediately reaching the photodetector. 圖 9：相機(jī)傳感器的前照式與背照式。前照式傳感器（CCD和早期的sCMOS）讓光線從正面進(jìn)入魏颓，在到達(dá)光電探測器之前缚去，通過微透鏡、電線琼开、電子設(shè)備等易结。背照式傳感器（EMCCD 和 BI sCMOS）具有翻轉(zhuǎn)傳感器，其中光線從“背面”射入，立即到達(dá)光電探測器搞动。
Every stage that light has to travel through will scatter some light, meaning that the QE of front-illuminated cameras is often limited from 50-80%, even with microlenses specifically to focus light onto each pixel. Due to the additional electronics of CMOS sensors (miniaturized capacitor and amplifier on each pixel), there can be even more scattering. 光線必須經(jīng)過的每個階段都會散射一些光躏精，這意味著前照式相機(jī)的 QE 通常限制在 50-80% 之間，即使使用專門用于將光線聚焦到每個像素上的微透鏡也是如此鹦肿。由于CMOS傳感器的附加電子元件（每個像素上的小型電容器和放大器）矗烛，可能會有更多的散射。
By rotating the sensor and bringing the photodetector silicon layer to the front (from the ‘back’), light has less distance to travel and there is less scattering, resulting in a much higher QE of >95%. While back-illumination was achieved earlier with some CCDs and most EMCCDs, it took longer for CMOS due to the complex electronics involved, and the specific thickness of silicon required to capture different wavelengths of light. Either way, the result is a good 15-20% QE increase at peak, and a 10-15% QE increase out to >1000 nm, doubling the sensitivity in these regions. The lack of microlenses also unlocked a new QE region from 200-400, great for UV imaging.
BI sCMOS have a much greater signal collection ability than FI sCMOS due to the increase in QE and the elimination of patterns/artifacts with a clean background. Along with the low read noise, BI sCMOS is able to match and outperform EMCCD in sensitivity, as well as already featuring much higher speed, resolution, and larger field of view.
Summary
Scientific imaging technologies have continued to advance from CCD, to EMCCD, sCMOS, and back-illuminated sCMOS, in order to deliver the best speed, sensitivity, resolution, and field of view for your sample on your application. Choosing the most suitable camera technology for your imaging system can improve every aspect of your experiments and allow you to be quantitative in your research. While CCD and EMCCD technologies enjoyed popularity in scientific imaging, over the past few decades sCMOS technology has come to the fore as an ideal solution for imaging in life sciences.
