CCD vs EMCCD vs ICCD: A Detailed Comparison

This article compares CCD, EMCCD, and ICCD technologies, outlining their differences. CCD stands for Charge Coupled Device, EMCCD stands for Electron Multiplying CCD, and ICCD stands for Intensified CCD.

Introduction

Scientific digital cameras come in four primary types, categorized by their sensor technology: CCD, EMCCD, CMOS, and ICCD.

CCD (Charge Coupled Device)

CCD transfers each pixel’s charge packet sequentially to convert the charge into a voltage. CCDs consist of an array of thousands or millions of light-sensitive elements, known as pixels, etched onto a silicon surface. Each pixel is a buried channel MOS capacitor. CCDs are fabricated using a p-type substrate, with the buried channel implemented by forming a thin n-type region on this surface.

The size of CCDs is specified in Megapixels. A megapixel value is equivalent to the multiplication of the number of pixels in a row and the number of pixels in a column.

CCD Structure

How CCD Sensors Work

Here’s how a CCD sensor operates:

• When the sensor array is exposed to light, the number of electrons (i.e., the quantum of charge) held under a particular pixel will vary directly with the luminous intensity exposure of that pixel.
• The charge is read out by suitable electronics and converted into a digital bit pattern, which can be analyzed and stored on a computer. This digital bit pattern represents the image.
• To record images in full color, a Bayer color filter array is bonded to the sensor substrate. This filter array consists of alternating rows of red/green and blue/green filters, also known as an RGBG filter. A particular color filter allows photons of that color to pass through to the pixel.

EMCCD (Electron Multiplying CCD)

EMCCD uses an electron multiplying structure on the chip. This allows EMCCDs to detect single-photon events without needing an image intensifier. The EMCCD has essentially the same structure as a CCD, but with a crucial addition: an electron multiplication register.

The stored charge is transferred through parallel registers to a linear register. Before being read out at the output node, the charge is shifted through an additional register—the multiplication register—where the charge is amplified.

EMCCD Structure

This amplification boosts the signal above the readout noise of the amplifier, giving EMCCDs higher sensitivity and speed than traditional CCDs. This enhancement comes from amplifying the charge signal before it reaches the charge amplifier.

ICCD (Intensified CCD)

To overcome the limitations of CCDs, the ICCD was developed. It utilizes optical amplification provided by an image intensifier to surpass the limits of a basic CCD sensor. ICCDs consist of an image intensifier tube coupled with a traditional CCD sensor device.

The light output of the tube is coupled with the CCD in two ways: using a fiber optic coupler or a lens. These coupling methods represent the two main types of ICCD construction. Lens-coupled types use a lens between the output of the image intensifier and the CCD, instead of a fiber coupler.

ICCD Structure

The major component in ICCD design is the power supply, which generates DC voltages and voltage pulses for its operation.

CCD vs EMCCD vs ICCD: Tabular Comparison

The following table compares CCD, EMCCD, and ICCD, summarizing their key differences: