SNR and Q of the Receiver

[senthilnathan.rajesh]

Hi....
Can anybody tell is there any relationship between Quality factor of Tuned Circuit (in Receiver Side) and the SNR of the Receiver....


Thanks

 

[RFDave]

There really isn't one.

Dave

 

[vfone]

There is an indirect relation.

Usually high Q of the tuned circuit means the insertion loss through the circuit is lower.

Lower insertion loss in the front of the LNA improves the system Noise Figure.

For the required RX sensitivity better system Noise Figure it will relax the SNR requirements (1 to 1 in dB).

SNR(dB) = 174(dBm) + RX_Sens(dBm) – 10*LOG(BW_Hz) – NF(dB)

 

[noiseless]

I think what senthilnathan.rajesh really want to ask is the relationship between Q and NF. Doess that high Q mean low NF, especially LNA?

 

[RFDave]

High Q can mean a Low Noise figure, but it's not sufficient. In this context, I'm taking Q to mean that the components have low losses, or small parasitic resistances. High Q parts won't degrade your noise figure as much as low Q parts, but unless the components are matched to the right impedances, it won't matter.

Does this help?

Dave

 

[vfone]

For two identical circuits having the same “best match” component values, the circuit which has higher Q it will have less insertion loss.
Otherwise nobody will care about Q of the components, which is a “killing” factor in Radio Frequency Design.

Following my explanation above, mean that the Q of the tuned circuits in the front of the LNA it will affect the SNR of the receiver.
Exactly what the initial question is about.