Output stage of CMOS Image Sensor's amplifier

[siegfi]

Deer all,
I've designed a CMOS Image Sensor first time.
I don't know how to design the output stage cause without any information about output loading.

One of my friend had told me set as 20pf cap and 1Meg Ohm resistor, cause this is the oscilloscope's input loading. But in this design would waste too much power on output stage.

Can any one help me?Thanks a lot....^^

 

[ambreesh]

Hi,
i hope you are using an Active pixel sensor.
And you are asking the output stage in an pixel sensor.
I hope all the MOS traansistor in the pixel are either PMOS or NMOS.
Kindly use a common drain amplifier at the output. The voltage would drop by threshold voltage.
In the reading circuitry use Correlated couble sampling to take care of FPN.
Hope it helps.

 

[dasong]

ambreesh ,can you tell me the most performance difference between 4T pixel and 3T pixel,thanks!

 

[fencl]

the key point in cmos image sensor pixel is fixed patten noise, by using cds 4T has better performance than 3t

 

[Old Nick]

FPN isn't that big a deal, because it's fixed. Dark image subtraction will take care of it. Depending on what you're designing your image sensor for (scientific measurement, low-light applications, portrait photography etc) different things will be a priority - noise, sensitivity, dynamic range etc.

As mentioned a source follower will do the job, also if you have the area available use a differential pair (better linearity). You'll also need to design an op-amp to drive any voltages off chip. Obviuosly the first thing this voltage wants to see when it gets off-chip is the input to another buffer.

APS sensors are fine, but if you're looking at high frequency stuff, then they are useless and you'll need to use a log-pixel (which also have a huge dynamic range, if that is important)