Ata_sa16
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Hi all,
I have designed some 50-50 matched LNA typologies. But when I design a front end on-chip mixer+LNA chain I confront an issue which really confuses me.
I have read some thesis and materials regarding this issue so I really want to dig this and get concrete answer and I would be really thankful and grateful if anyone give me advice in this case.
______________________________________________________________________________________________________
Imagine you want to simulate LNA which is going to be connected to mixer within chip (there is no matching between LNA & Mixer).
I have seen two methods
1) Mixer has been already designed and we measure input impedance of mixer (Zin mixer). Therefore when we design LNA we use output port which has real and imaginary part equal to Zinmixer real and imaginary part. So we measure S11, S21 ... NF and P1dB and etc.
The question is we may need to know LNA's output impedance to design Mixer ?
2) Second approach is used in Professor Behzad Razavi's book. It is emphasized that we have to care about voltage quantities in integrated circuit design.
So there is no port at the output and AC simulation is done. so we check AC gain (vout/vin) not S21 and basically we do not need output port or what ??
Even if you ignore mixer's input impedance (lets say you include Cload only) you have to put a port at the output of LNA to simulate NF since simulator need input and output port to plot NF.
What are the correct simulation steps to observe the real gain (or S21) or do we even care about S21 or not ?
What are the steps to observe other specs like NF and P1dB compression point for LNA ?
This is biggest question of my life ! If I totally get a concrete answer I would be more than happy
Thank you for your valuable time and effort.
I have designed some 50-50 matched LNA typologies. But when I design a front end on-chip mixer+LNA chain I confront an issue which really confuses me.
I have read some thesis and materials regarding this issue so I really want to dig this and get concrete answer and I would be really thankful and grateful if anyone give me advice in this case.
______________________________________________________________________________________________________
Imagine you want to simulate LNA which is going to be connected to mixer within chip (there is no matching between LNA & Mixer).
I have seen two methods
1) Mixer has been already designed and we measure input impedance of mixer (Zin mixer). Therefore when we design LNA we use output port which has real and imaginary part equal to Zinmixer real and imaginary part. So we measure S11, S21 ... NF and P1dB and etc.
The question is we may need to know LNA's output impedance to design Mixer ?
2) Second approach is used in Professor Behzad Razavi's book. It is emphasized that we have to care about voltage quantities in integrated circuit design.
So there is no port at the output and AC simulation is done. so we check AC gain (vout/vin) not S21 and basically we do not need output port or what ??
Even if you ignore mixer's input impedance (lets say you include Cload only) you have to put a port at the output of LNA to simulate NF since simulator need input and output port to plot NF.
What are the correct simulation steps to observe the real gain (or S21) or do we even care about S21 or not ?
What are the steps to observe other specs like NF and P1dB compression point for LNA ?
This is biggest question of my life ! If I totally get a concrete answer I would be more than happy
Thank you for your valuable time and effort.