[SOLVED] Bad S11 and S22 after impedance matching

[Murazan]

Hello,
First of all I am new in designing RF circuits from scratch, and also new in using ADS program. I have been tasked to make an LNA and thus followed this video and this video to learn it step by step. I'm using the same transistors, same technique, etc. with the main difference is my working frequency is 960-1215MHz. I have managed to built the schematic up to doing impedance matching. But in this step, I am very confused because my LNA constantly getting poor S11 and S22 performance. And if I try to improve one, the other will have worse performance. I have attached the schematics. Any suggestion and recommendation are welcomed.

Thanks in advance.

 

[BigBoss]

Refer to "Simultaneous Matching" in textbooks.If your goal is to obtain Minimum Noise Figure, S11 or S22 maybe both can be bad, it's not surprizing.
All depends on you target.

 

[Murazan]

Refer to "Simultaneous Matching" in textbooks.If your goal is to obtain Minimum Noise Figure, S11 or S22 maybe both can be bad, it's not surprizing.
All depends on you

My target is to have a compromise between good noise figure and a good return loss. So far the noise figure side is quite acceptable (less than 1.5db over the bandwidth) and quite good S22 (< -10dB) but the caveat is very poor S11. I have tried to improve S11 to an acceptable level (around -10db just as benchmark) but this is hurting the S22 performance as well.

 

[D.A.(Tony)Stewart]

What are your specs for good/bad?

Have you chosen extreme W/L and L/W ratios for a good reason?

 

[Murazan]

What are your specs for good/bad?

Have you chosen extreme W/L and L/W ratios for a good reason?

Having Noise Figure < 1.5 dB, S11 and S22 both < -10dB. For the W/L and L/W ratio, I haven't studied this yet

 

[BigBoss]

Draw Noise Circles and Compare them with S11 and S22. Then find a compromise Point that will give you an Acceptable Noise Figure and good Reflection Losses.

 

[Murazan]

Draw Noise Circles and Compare them with S11 and S22. Then find a compromise Point that will give you an Acceptable Noise Figure and good Reflection Losses.

Okay, thank you. Turn out the problem is with the circuit itself. The problem have been solved. thank you for all the help