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Simulators >> RF Simulators >> How to set the correct Testbench for differential LNA!
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Message started by Jack on May 18^th, 2009, 4:21am

Title: How to set the correct Testbench for differential LNA!
Post by Jack on May 18^th, 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!

Title: Re: How to set the correct Testbench for differential LNA!
Post by Jack on May 18^th, 2009, 4:24am

This is testbench 1

Title: Re: How to set the correct Testbench for differential LNA!
Post by Jack on May 18^th, 2009, 4:24am

This is testbench 2

Title: Re: How to set the correct Testbench for differential LNA!
Post by Jack on May 18^th, 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.