Help me design a LNA with input limiter
my MSN: zthhxiexie@hotmail.com
You can try to do as follows:
1) added a shunt diode at input part of your LNA, normally its onstate volt is about 0.3V, is equal to 0 dBm in dBm, if input power higher than 0 dBm then this diode will is in onstate to avoid to spoil transistor(or FET, HEMT) owing to injecting high power.
2) I know LNA is a linear circuit, its typical state is in low power. but I think 0 dBm input power can't injure the transistor(or FET, HEMT), you can see its datasheet, normally is something about this there.
Dear,
Try using Pin-Diode (or Schottcky Diode) Limmiters.Packaged & Drop-in versions are available.
check this link for example:
http://www.microwavedistributors.com...idisco2004.pdf
Good Luck.
thanks .i will try .
but whether the PIN diode can hold +35dBm input power ?
Yes, I agree with your opinion. You should choose a diode can held +35dBm(3.16W).
so what can i do ?
i want to use a switch,such as HMC484MS8G,and detect the input power,if the power is larger than -10dBm ,then change the switch.
is it possible?
in my opinion, it is possible but complex. You have to concern these factors including switch time of switch, response time of detector, I think you should confirm that microwave energy is can't spoil the amplifier in time that is sum of detector response time and switch time.
hi Wnnedi in ur previous reply u mention that 0.3V is equal to 0dbm, could u pls guide me how to calculate this power.
Yes, a typical PIN diode limiter can handle 36 dBm very easily, since almost all of that power is reflected back out of the antenna when the limiter turns on (acting like a short circuit). So very little of the input power is actually turned into heat in the diode.
That said, if you expect fairly routinely to be handling this overload, You should design the limiter with a diode that is heat sunk well enough to dissipate the heat--either a chip limiter diode epoxied right onto a metal housing, or a packaged diode where the package has a low thermal resistance (i.e. no flying lead or surface mount styles).
36 dbm should be able to bias up a limiter diode fairly easily. You need series caps to DC block the diode from the antenna and receiver, and a DC return, such as a inductor and small value resistor to ground.
If you need a limiter that will activate at much lower power levels, you have to have a two section limiter, with a limiter diode that is DC biased on by a power detecting schottky diode.
See this link for the conversion to dBm: http://en.wikipedia.org/wiki/DBm