What is a floating diffusion(FD node) in image sensor pixel?

[leohart]

floating diffusion

what is a floating diffusion(FD) exactly?In most figures it is illustrated as a
parasitic diode,or maybe including the parasitic gate cap and parasitic drain/source
diffusion cap(not sure about this)?
but why it is called FD node?

 

[ch1k0]

fd node

FD where is charge stored for readout in photogate pixel sensors.
Name same from CCD output amplifier stage. photo carriers pushed to FD node at readout.
if helped push button!

 

[leohart]

sensor fd floating diffusion

I would like to push the button for you~ XD
But what you have said is all that I have already known...
Actually,the point is not what is a FD used for,but what consists a FD and why it is called a FD(the source of the name)

 

[n1cm0c]

floating diffusion capacitance

I think that he says that floating diffusion is the name given to the node in CCD output stages, where the charge packet is dumped into a FD node that only connects to the gate of the output buffer amplifier (a source follower).
Since it's the only diffusion node in a CCD device, this is propably the reason it's called a floating diffusion.

Active pixel sensors copied this concept , since they implement effectivelly the last stage of a CCD line.

Is this your question, the origin of the name, and you know all else ?

 

[leohart]

hmm,a bit more clear,but what does floating mean here?

 

[leohart]

I have consulted a expert and got the answer as below:FD is isolated from PD/PG by disable the TX gate,and so it is floating...

 

[ch1k0]

Re: What is a floating diffusion(FD node) in image sensor pi

good for aps, but ccd has FD!

see explanation figure

 

[leohart]

Re: What is a floating diffusion(FD node) in image sensor pi

good for aps, but ccd has FD!

see explanation figure

I have check the png file,the same mechnism in both aps and ccd~Actuaaly aps borrow this FD from CCD to increase conversion gain.

I'll push the button for you my friend,thx for the pic,it really helps

 

[timof]

Re: What is a floating diffusion(FD node) in image sensor pi

"Floating diffusion", also called "sense node", is a region in active silicon (diffusion) region electrically isolated from all other nodes. It's a quasi-neutral region (i.e. it's not fully depleted) isolated by p-n junction from other nodes. There is no metal contacts to this region. Thus, it's potential is determined exclusively by the amount of charge stored in it, and its capacitance. Capacitance of this region is usually very low, to achieve high conversion gain, i.e. the change of its potential/voltage with the addition of one electron. It's potential can also be changed by swinging the voltage on neighboring nodes (i.e. gate of the reset transistor), due to capacitive coupling.

So, the "diffusion" comes from the fact that this region is located in Si diffusion. "Floating" means that it is not connected to any of the fixed/controlled voltage nodes, its potential is "floating".

Before the readout, the floating diffusion is reset (emptied of non-equilibrium carriers). During the readout, the electrons accumulated in the photodiode are transferred to the floating diffusion (by opening transfer gate). It's voltage changes, and this change is amplified by the source follower and read out.

 

[zohair2]

Re: What is a floating diffusion(FD node) in image sensor pi

good for aps, but ccd has FD!

see explanation figure

hi friends . could u please tell me where is this png file taken? i want the name of this book please .. sorry for my interrupt

 

[keith1200rs]

I am not sure, but it may be ISBN 978-0-7923-3456-9

Solid-State Imaging with Charge-Coupled Devices by

Albert J. P. Theuwissen

Keith.

 

[ahgu]

Re: What is a floating diffusion(FD node) in image sensor pi

Is it possible to do the similar thing for InGaAs image sensor? I notice each InGaAs pixel is followed by a transimpedance amplifer. Can they do the CCD implementatation where they transfer charge from this pixel to next pixel? instead of using an amplifier for each pixel, for noise reduction reasons? and use floating diffusion as the output. The sensitivity for InGaAs is very low due to the larger capacitor in the transimpedance integetrator amplifier.

"Floating diffusion", also called "sense node", is a region in active silicon (diffusion) region electrically isolated from all other nodes. It's a quasi-neutral region (i.e. it's not fully depleted) isolated by p-n junction from other nodes. There is no metal contacts to this region. Thus, it's potential is determined exclusively by the amount of charge stored in it, and its capacitance. Capacitance of this region is usually very low, to achieve high conversion gain, i.e. the change of its potential/voltage with the addition of one electron. It's potential can also be changed by swinging the voltage on neighboring nodes (i.e. gate of the reset transistor), due to capacitive coupling.

So, the "diffusion" comes from the fact that this region is located in Si diffusion. "Floating" means that it is not connected to any of the fixed/controlled voltage nodes, its potential is "floating".

Before the readout, the floating diffusion is reset (emptied of non-equilibrium carriers). During the readout, the electrons accumulated in the photodiode are transferred to the floating diffusion (by opening transfer gate). It's voltage changes, and this change is amplified by the source follower and read out.