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ADS question

ADS question

ADS question


I am simulating an LNA for NF. I loaded the antenna S parameters to the input port. But when running the simulation there was a problem "No DC convergence" I am using a spice model for the main transistor. Simulating the LNA with 50R is ok, but the problem comes when loading the antenna S11 into the port 1.

Does anyone have an idea of what´s going on?


RE: ADS question

Sounds like you are using the non-linear analyzer.  Did you remember to include the bias lines/dc voltages/DC blocks?


Maguffin Microwave wireless design consulting

RE: ADS question


yes, I used the DC blocks, it´s a good point.

When I used a 50R input port the circuit works perfectly, without problems. When I replace the 50R by a S1p file then ADS says "No DC convergence". Strange!!!

I you have any other ideas they will be welcome!


RE: ADS question

What happens if you put a (virtual) high value resistor, like 100K ohms, between the input and ground? Just to give the algorithm something to work with. This is based on the assumption that your antenna element is essentially an open circuit at DC.  

RE: ADS question


I have tried that but it didn´t work.

I have attached the ADS file in case you have time and can have it a look. When I load the input with a 50R port the circuit works fine, but when I load the antenna impedance then there are some problems, before I had the "no DC convergence" then I changed the way to import the antenna impedance and now it has some problems at one frequency, strange!


RE: ADS question

Well if 50R works and 100K doesn't, then as a first step perform a log-scale binary search pattern to see where it stops working. If it requires 5K (for example) instead of 100K, then at least it might help you to get started again.


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