Thank you.
I think in the end I will have to replace real inductors (inductors from TSMC 0.13um) and simulate again. Is that right?

I mean that at first, for the simplicity sake we replaced real inductors by an ideal inductor and ideal resistor in series. However, when all things complete, we need to use real model, pick inductors from TSMC 0.13um that have almost the same parameters such as inductance and internal resistance.

Hi,

I run Gmax and NFmin with Vgs to choose bias voltage. I have just seen another method is to plot gm, gd0, Vgs as functions of current density Id/W. And from that choose optimum drain current density for minimum NF.

Is there any difference between two methods? I see that the first one is much more simple but don't know if there is any problem with it?

Hi,

Could you take a look at the procedure to design a LNA at near the end of the page?
http://www.ece.ucsb.edu/yuegroup/Teaching/ECE219Winter2013/Lecture%20slides%20an...

The second method that I said in in step 3.

"For a minimum channel-length device, plot (by simulation or otherwise) gm, gd0, and VGS as functions of current density ID/W"

I'd like to ask another question about minimum noise figure NFmin. As far as I know, NFmin depends only on the geometry of the two transistors. For my example, NFmin will change as dimensions L and W change. This is where I get confused about the procedure to design LNA.
As in the procedure, first we simulate NFmin vs Vgs (bias voltage). From that we can choose Vgs that sastifies NF requirement.
After fixing Vgs, we scale W and L of transistors to get NFmin. This is where the problem is.

For example, initilally, we set W1 and L1 for transistors to simulate NFmin vs Vgs.
From the plot of NFmin vs Vgs, we choose Vgs and fix it.

After fixing Vgs, we scale W1 and L1 to W2 and L2 respectively to get NFmin. However, when W and L are set to W2 and L2, NFmin will be changed. It is no longer the initial NFmin that we choose above.

Finally, what is the point of simulating NFmin here?
Thank you.

Hi, Aaron.

I would like to ask a question. My input is matched. Z11 = 50 Ohms with Real{Z11} = 50 Ohms and Im{Z11} = 0.01Ohms.
However, I checked S11 and it it still large (about -6dB). Could you explain why?

Thank you, Aaron. I used two ports.
I will try your solution now. BTW, I made a new thread for this topic with some more information.

Hi baab,


obviously I haven't seen your schematic, but I guess that S12 is very poor. If you want to know more about s-parameters, you should read that book I mentioned before, "RF Circuit Design" by Chris Bowick.

To give you a watered down explanation, you can say that S11 is defined when the load is equal to 50 ohm (again this isn't exactly true and you need to read to understand more). On the other hand, Z11 is defined when the load is an open circuit. So that's why you're getting different answers. If S12 is very good, then it won't make much difference whether you look at S11 or Z11.

You should try and improve S12 maybe by using a cascode transistor for example.


regards,
Aaron