Some technical queries about LNA

[ahmer saeed]

I have designed the LNA using atf 36077.The gain I achieved is about 8db at NF 0.3 db.What problem may i face practically due to this low gain?

 

[Mazz]

If you're using this LNA (as I suppose) in a receiver, with a low gain, the overall receiver NF will be degraded by the other components in the receiver chain (mixer, agc ....).
Using linear (non in dB) quantities:

Cascade noise factor: Feq=Flna+(Fother-1)/Glna

if for example NFother= 5 dB, overall NF=1.5 dB with your LNA in front.

Be aware of this.
Mazz

 

[VSWR]

According to the ATF-36077 data sheet (**broken link removed**), the transistor has the following performance:

Noise Figure (Tuned Circuit): 0.3 dB @ 4 GHz, 0.5 dB @ 12 GHz
Gain at Noise Figure (Tuned Circuit): 17 dB @ 4 GHz, 12 dB @ 12 GHz

Your 8 dB of gain seems too low. Can you provide your LNA design files so we can try to help you?

 

[activewei]

Potential problem is
1) Insufficient AC isolation of the DC bias network.

2) Improper grounding of the amplifier.

3) Type of capacitor used.If the operating frequency is at 12GHz and you are using normal DC block capacitor, the ESR will be high leading to gain drop. (Recommend: ATC 600S series capacitor)

4) Substrate used. Again if the operating frequency is at 12 GHz, using FR4 will lead to significant gain drop.

If you want to know more, tell me your operating frequency, substrate used, and type of DC block capacitor being used.

 

[yuppi77]

Hi,

Another factor to this low gain could be Mis-matching.

By the way, could you let us know the operating frequency for your LNA design.

Thanks.