Dear researchers ,
I am simulating a cascode common source LNA (low noise amp) in 0.18um tech in cadence in ISM band of 902 -928 MHZ with the supply voltage of 0.9 v but , although all my transistors are in region 2 , cant get gain and my S21 is negative in dB
does anyone know where the problem is ?
p.s : the power consumption should be sub mW
all the components are from tsmc0.18
Dear Ava,
One of the important issue for the S21 is the matching at the amplifier ports. Normally the source impedance in measuring the S parameters is 50 ohm and also the load resistance is 50 ohm. If you do not have matching at the ports this will decrease S21 and if the mismatch is sever the overall S21 will be less than one even if the amplifier block has gain.
You have to match the amplifier at both the input and output to get the gain of the amplifier block.
You can use circuit analyser such as SPICE to calculate the voltage gain of the amplifier for verifying the gain of the amplifier block.
If S21 is smaller than one its dB will be negative.
Best wishes
Aparna Sathya Murthy Abdelhalim abdelnaby Zekry
thanks for your answers
i attach some of the plotted results
i am not sure if the S22 or the real part of Z22 is correct or not because it is bounded to the output port that its resistance is 50 ohm
Dear Aparna Sathya Murthy
you mean the Dc current from the path print ....> Dc operating point ?
I bounded the body terminals to the ground
Dear Ava,
It seems that the input matching is okay since S11< -10 dB but the output matching may be not acceptable since it is above much above -10 dB.
However, i believe that it is not the cause of the low S21. I see that your amplifier block must be redesigned to keep the matching while increasing ts gain. This is basically accomplished by increasing it transcondcutance gm which can be realized by increasing its bias current as Aparna hinted.
Best wishes
Aparna Sathya Murthy
yes its high but i think if i can improve gain the NF may reduce
I am trying to redesign the amplifier and after setting dc bias i try transient analyse but i am not sure the output waveform are correct or not? i expected that amplitude of output increase but its not
the question is which parameters effect on output amplitude ?
- Badges
- Science method