LNA Design in Agilent ADS

Dear Friends,

I am really curious that what is the meaning of simultaneous-match input/output impadances or simultaneous-match input/output reflection coefficients in Agilent ADS . For the LNA design, after plotting gain and noise circles I match the input of the device. Now I need to match output but whatever I place at output will effect input section also. What should I do? Are these simultaneous match devices for this purpose?

Regards,

1st match input for NF, then match output for Gain, then make a tradeoff between two matches.

If you get really deep into microwave circuit theory, you'll find that the equations for matching transistors are not explicit, and therefore require an iterative solution. So, like tony said, match the input for best NF, then output for max gain, then bounce back and forth until you hit a sweet-spot, or give up a little gain to improve the NF, or vice-versa, depending on which performance parameter is more important. (HINT: NF is generally the most important, especially on the first LNA in your receiver chain... if you can get a low NF up front, then you can add LOTS of gain behind it and not significantly reduce the overall NF of the receiver)

From microwave theory, when you have the [S] parameters of your amplifier (with stability assured by proper nets), there are in general tree type of matching you can perform

1) Simultaneous-complex conjugate matching: In this case the teory gives to you the formulas to obtain two load that inserted at input and output of your device assure the maximum available gain (MAG)

2) Matching with the optimum load at input for noise: the theory gives to you the load that assure the minimum NF (load at center of the circles of constant noise), in this case the output shall be matched with the complex-conjugate approach

3) Matching at the output of the device to guarantee the maximum achivable power by using a load that assure the maxiumum excursion of voltage and current simultaneoulsy

thank you,

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