View attachment 119559
Hi biff44,
Thank you for your reply. The interconnecting transmission line is about 1.5cm. The working frequency is from 1.2 GHz to 1.6 GHz and the wavelength is about 12 cm. In fact my whole design process is this:
1) I choose a optimum source reflection coefficient Γs=0.3165∠83° on Smith Chart for LNA based on the equal gain circle and equal noise figure to get the ideal gain and noise figure.
2) I then did the input matching to 50 Ohm for the chosen Γs using LC network as you can see in the attached image.
3) I calculated the corresponding ΓL = 0.529∠61.3° using formula in the attached image in order to do conjugate matching.
4) Match the calculated ΓL to 50 Ohm using one LC network1 (C3, L2), then using another LC network2 (C4,L3) match 50 Ohm to 75 Ohm of the input impedance of MAX2112.
So my question again:
1) do you think matching the calculated ΓL to 50 Ohm not necessary or matching 50 Ohm to 75 Ohm not necessary? Will it have best gain and noise figure if I do both?
2) do I need to add DC isolation capacitors in serial for both input and output of LNA? What if I add a 470 pF DC isolation capacitor or another LC network with large values( say 470pF capacitor in serial and 56nH inductor in parallel) for both input and output? Do you think it is a good idea and necessary?
Thanks and regards.