But my question here is for the upper transistor (stacked transistor) in one-stage cascode Source-degeneration LNA. Which region should it work? Saturation or Linear region?
I think it is better in saturation region to make sure your LNA more stable!
Eventhough linear region provide smaller current and act like an active resistor, it's better to have a stable transistor...especially on LNA!
The transistor you mentioned is the top one, which I mentioned?
I have seen one one-stage cascode source-degeneration LNA with frequency 2.4GHz. It had pretty good performance(with very good simulation results for every aspect), I found that the bottom transistor was in saturation, while the top one was in linear region. I was confused. That's why I asked this question.
So, do you think this LNA design was not that stable?
guamak_menanak said:
I think it is better in saturation region to make sure your LNA more stable!
Eventhough linear region provide smaller current and act like an active resistor, it's better to have a stable transistor...especially on LNA!
The transistor you mentioned is the top one, which I mentioned?
I have seen one one-stage cascode source-degeneration LNA with frequency 2.4GHz. It had pretty good performance(with very good simulation results for every aspect), I found that the bottom transistor was in saturation, while the top one was in linear region. I was confused. That's why I asked this question.
So, do you think this LNA design was not that stable?
guamak_menanak said:
I think it is better in saturation region to make sure your LNA more stable!
Eventhough linear region provide smaller current and act like an active resistor, it's better to have a stable transistor...especially on LNA!
It is better to have all the transistor in the saturation region, to make sure that your design is stable if there are some voltage drop.
I'm not very sure on why sometimes we used linear transistor, if i'm not mistaken transistor in linear region act like a resistor. Furthermore, someone told me that linear transistor can save the power consumption.
Etahn = as for me, I'm using all the transistor in the saturation region. It makes my design simpler and easy to calculate
hi to all
both transistors MUST be in saturation only....M2 in saturation behaves like a common-gate stage and its input impedance is approximately 1/gm. This low load value helps reduce the miller effect thru cgd of M1 thereby making it stable. this is why M2 must be in saturation. as only then will it act as a very good current translator while giving low input impedance to M1. I have never heard of M2 being in saturation...as there does not seem to be advantages!!!
I think if transistor work in saturation the out put is not exactly related to input so information get lost!so for LNA i think it should work in linear.isn't it true?