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About the LNA corrupted with relationship in High power input

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Jameslu

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Assume the LNA operation frequency in 150MHz,
if another frequency radiation the high power in to LNA , LNA will corrupted?
 

pavel_adameyko

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Hello
Yes, of course. Gain of LNA at working frequency would drop and also NF would increase - you can simulate this effects.
 

Jameslu

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thanks your reply in it, i'm agree you
but my problem is ,then another frequency include high power radiation , it will incident to my LNA still damage
i don't understand this problem the root cause ?
 

tony_lth

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LNA has a bandwidth, so if you don't have a filter between antenna and LNA, the interfere will cause damage.

---------- Post added at 04:31 ---------- Previous post was at 04:30 ----------

The LNA has a max input level, if exceed the level, the LNA will possibly damaged.
 

Jameslu

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thanks your reply in it ,
i was simulation from ADS, assume matching impedance of the LNA at 150MHz,
and i was set input power of the two tone (150MHz , 1GHz) at -40dBm and 0dBm , The result power level in 1GHz than 150MHz to low,
i think that a phenomenon , maybe it possible that can't to import to high power on other frequency.
 

tony_lth

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thanks your reply in it ,
The result power level in 1GHz than 150MHz to low,
i think that a phenomenon , maybe it possible that can't to import to high power on other frequency.

I can't understand your questions clearly.
What is your LNA component? If its working band is larger than 1G, then 1G is amplified. And the 0dBm of 1G maybe destroyed your LNA.
 

RCinFLA

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All CDMA phones have this issue since the transmitter and receiver run at the same time. They have a dual filter known as a duplexer. One filter passes Tx frequency and attenuates at Rx frequency to avoid spraying the Tx PA's broadband noise across the receive band. The other filter is the Rx side path which attenuates the Tx frequency to avoid it overloading the receiver stages while passing the receiver frequencies.

The problem is dynamic range. At RF power levels long before there is enough power to literally shut down the LNA there is damage done by intermodulation products that cause interference on the receiver RF channel.
 

Jameslu

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tony_lth thanks your reply,
sorry!!i am description problem condition are not enough,
i was repeat description this problem condition give you
my product include the GSM System , but the GSM will interference to receiver of VHF band
and the high power of the GSM will import to LNA of the transistor, and the transistor been to damage.
but the GSM antenna close to VHF band antenna.
i'm think the Phenomenon of this problem , Have a possible the GSM antenna close to VHF antenna ,and coupling the high power
in to LNA of the transistor and it was damage,

---------- Post added at 16:57 ---------- Previous post was at 16:46 ----------

RFinFLA thanks your reply,
i am understand ,Between antenna and RF system have a filter,but my system have't.
maybe i am discovered the problem .
 

tony_lth

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The space of the two antenna should be at least 4-5 wavelengths away. Say 300M, the wavelengths is 1m. SO maybe you can arrange the two antenna at least 5 m.

---------- Post added at 08:58 ---------- Previous post was at 08:34 ----------

Say GSM power is +50dBm, the GSM antenna have 20dB gain, so GSM emits about +70dBm. Say the coupled cofficient is -30dBc. So GSM signal input your VHF antenna is +40dBm. You VHF antenna gain for GSM is -10dB, so input your LNA GSM power is +30dBm. That can destroy most of the LNA.
Say your VHF LNA IP1dB is -10dBm, so you need a filter than can supress the GSM about -40dB. To make sure your VHF LNA work in linearity, at least you need to supress the GSM about -60dB.
So you need a filter that have insertion loss about 0.2dB for VHF, and 60dB for GSM.
Hope this can help you.
 

Jameslu

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thanks your reply

My system only one RX system, and we want to cost down , so not use filter .
but now, we are possible to use filter in RX system to fixed.
 

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