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How to set the correct Testbench for differential LNA! (Read 4087 times)
Jack
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How to set the correct Testbench for differential LNA!
May 18th, 2009, 4:21am
 
Dear All,

   I am design a fully differential Low noise amplifier, which should be connecting with the next stage mixer. Because I want to design the monolithic LNA and mixer, so I don't consider the input impedance matching between LNA and mixer.

   When I use testbench 1 as shown in figure1, at the output I use ideal transformer (2:1) to realize the diffferential to single end, then add the port(10kohms) and load capacitance(100fF) as the input of mixer. It gives the good results.

   However when I use the test bench 2 as shown in figure 2, at the output I connect the output of LNA to the biased MOS transistor directly, but the frequency response of the LNA is totally changed. I don't know the reason.

   Which one gives the correct results, and what is the difference between the two test bench.

   Thank you very much!
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Jack
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Re: How to set the correct Testbench for differential LNA!
Reply #1 - May 18th, 2009, 4:24am
 
This is testbench 1
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figure1.jpg
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Jack
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Re: How to set the correct Testbench for differential LNA!
Reply #2 - May 18th, 2009, 4:24am
 
This is testbench 2
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figure2.jpg
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Jack
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Re: How to set the correct Testbench for differential LNA!
Reply #3 - May 18th, 2009, 4:30am
 
I think if the input stage of the mixer is llike the one shown in figure 2, at the input, the bias resistor with the gate-source capacitor of the transistor will operate as a low pass filter, I think maybe it is the reason why the frequency response is changed throughly. Any comments will be appreciated.
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