LNA transient analysis

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Hello

I need an urgent answer. I am designing LNA and I am checking s parameters, dc parameters, ip3, p1db etc to check its performance. Now the question is I am also doing transient analysis and checking the waveforms at various nodes of the LNA.

If for any DC baising, I see that waveforms are losing their sinusoidal shape, I try to modify the biasing to get the wave shape correctly. Am i doing ok?? or while designing LNA i should not check wave shape whether it changes from sine (at input) to some new shape (at output)?

an early respose will be very much appreciated. Plz also clarify what is the purpose of transisnet analysis in LNA
 

LNA is usually used to amplify the very small signal (uV~mV), so you have to ensure the swing in the the transient simulation
 

Thank you for the reply. One another question is if S21 is a power gain and I get it from s parameter simulation of LNA. Then how can I find the voltage gain from this power gain in dB?

I have seen papers that when they have small power gains they report voltage gain so I need to know.

thanks in advance
 


If i understand correctly, than:

1. If impedances equal, than simple Power gain = Voltage gain
2. if impedances not equal we can do some math:

\[Gpow_{dB} = 10 * log(\frac{P_{out}}{P_{in}}) = 10 * log(\frac{V_{out}^2 * R_{in}}{V_{in}^2 * R_{out}}) = 20 * log(\frac{V_{out} * R_{in}}{V_{in} * R_{out}}) = 20 * log(\frac{V_{out}}{V_{in}}) + 20*log(\frac{R_{in}}{R_{out}})\]

and therefore
\[Gvol_{dB} =Gpow_{dB} - 20 * log(\frac{R_{in}}{R_{out}})\]
 

definition of s21 is the voltage gain, |s21|^2 is the transducer power gain. For your transient simulation: it depends on the strength of your input signal, maybe your transistor is already in saturation. maybe post your results.
 

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