Frequency Scaling parts from 900MHz down to 300MHz

[infinite_gbps]

Hi Everyone,

I am looking into using this Avago LNA and they show an application note for 900MHz (see link) where they show the component values.

**broken link removed**

How can I use the exact same design at 300MHz? I don't know how to do it but I image that I have to do some sort of frequency scaling of the component values for the frequency I am interested in. The design in the application note is for 50 Ohms and so would mine.

Thank you.

 

[BigBoss]

No.. You cannot do by scaling the component values.
Even you assume that perpipheral components are ideal and they have no change on their characteristics, active devices are not so..
You should design an LNA by " inspiring" from actual LNA..
Otherwise the designs might be sooo easy...:lol:

 

[infinite_gbps]

Can you help in getting the component vales for this part at 300MHz?

According to the data sheet:
**broken link removed**
"Essentially, C1 & C2 at the RFin & RFout are DC blocking capacitors. L1 is input match for noise figure and L2 is output match for OIP3. C3, C4, & C6 are bypass capacitors. R2 is stabilizing resistor [whatever that means] and Rbias is the biasing resistor."

So for a proper design I don't see the bypassing and DC blocking caps changing. Am I wrong? Same for the Rbias in my mid. So the knobs I think I have are L1, L2 & R2.

 

[vfone]

Avago specifies that the optimum minimum frequency of this circuit would be 450MHz.
Before doing any NF optimization, if you place the provided S-parameters in a simple simulator you will see that this circuit has a lot of gain and is very unstable at 300 MHz. The NF is also increasing at lower frequencies.
At this relative low frequency I don't think it will work better than any cheap BJT, SiGe, or FET transistor.

 

[infinite_gbps]

Avago specifies that the optimum minimum frequency of this circuit would be 450MHz.
Before doing any NF optimization, if you place the provided S-parameters in a simple simulator you will see that this circuit has a lot of gain and is very unstable at 300 MHz. The NF is also increasing at lower frequencies.
At this relative low frequency I don't think it will work better than any cheap BJT, SiGe, or FET transistor.

Avago shows that their LNA is stable even below 450MHz in their data sheet - page 8. I looked at their K-factor calculations which should be based on their S-parameters.

Did you look at the s-parameters and saw that it was unstable?