CMOS noise model in saturation and linear region
I know there are shot noise, thermal noise and 1/f noise in the CMOS transistor. CMOS has the saturation and linear region. Is the noise model same in these two regions? Or the noise model is available in the saturation region only?
Best Regards,
wccheng
Frankly, the noises are due to the problems in processing, which are more physical. The regions Saturation and Linear are electrical. The reason why we are concerned in saturation is because it is where you do the signal processing. In digital circuits, the device noise is not really predominant. Hence we do not bother there.
Most fets have processing "problems". Problems involve things like crystaline structure defects at interfaces. These defects cause traps, where carriers can be "hung up" for a while, and released randomly in time, causing noise. Whenever you run such a device into saturation, where the fields are wildly changing at these interfaces, you end up with the most shot noise. So I would expect a cmos device to be much noisier in saturation.
As far as digital noise, yeah. If you are concerned about timing jitter on an OC-12 link, it is a big deal.
One must remember that :
Shot noise is due to the crossing of the Junction of holes/electrons in a random manner. When they cross the junction with some junction potential ψ, they reach the other side to become the minority carriers. Hence their motion is actually random when we assume it to be continous.
Thermal noise is due to the thermal velocity of carriers. The thermal velocities are more than the drift velocities. Hence they cause a noise due to it which depends on temperature
Flicker noise is due to the fact that some carriers are trapped in the Si - SiO2 interface and are rapidly changing their states.
From the above things, we should note that there is no mention of the region of operation. But mostly in saturation, the fields are high and will cause much worser noise conditions.
Is there any nice book for this topic?
Try paul Gray and Meyer
also try Behzad Razavi's CMOS analog integrated circuits
In saturation region MOS transistors has very large noise ,but in linear region when we use transisto as a switch we can obtain low noise
Check this document, talks about types of noise.
Regards.