Hello,

I was reading the datasheet of AD9272 and I can't understand what does it mean with "combination" of Rfb1 and Rfb2 (of Figure 38) to give an equivalent "Rfb" (in equations 1 and 2), when they talk about active impedance matching. Also, what does the capacitor Csh do at the input of LNA?

Thank you.

Datasheet: http://www.analog.com/static/imported-files/data_sheets/AD9272.pdf

Hello Darius,

The "combination" of Rfb1 and Rfb2 means that the resistors are in parallel so it is the effective Rfb is equal to Rfb1||Rfb2.

Csh is used if the input impedance (Rin) of the LNA is less than 100-ohm. It would only be less than 100-ohms if the active termination was used and set Rin <= 100-ohms. Csh helps with the stability of the LNA at low input impedances.

Regards

Gina