Hi Guys
I have designed a differential LNA. I get a good voltage gain of 27dB.

The Problem is that i donot know how to calculate the Noise Figure of the design using SPECRE RF!!!!

I know how to do S-paramter simulation in SPECTRE RF but i donot know how to find Noise Figue from that.

What else does SP analysis in SPECTRE RF  tell me and how?

Can anyone help me with this.??
Thanks

Hi,

while doing sp analysis, In the choosing analysis form for "sp" analysis

I select start-stop for Sweep Range and the range i enter is :
Start : 800 M
Stop:  5 G

But when i simulate i get the following error:

Error found by spectre at freq = 800 MHz during SP analysis `sp'.
'iprobe' or 'oprobe' did not appear in the first or the second entry in 'ports' parameter. Respecify 'ports' parameter and start again.

any ideas how to solve the problem?

Hi
thanks for the reply, I seek help but for that i need to specify the problem in detail. Here is the detail ..

I have a differential LNA with output pins as out+ and out-. At the outputs I have stuck in two "psin" ports, one at each differential output.

At the input side, again i have two "psin" ports , one at each differential input.

Now I do "sp" analysis.
If I highlight "NO" in the "Do Noise" field, the sp analysis works and i am able to plot S11, S22 etc.

But the problem starts when i highlight "YES" in the "Do Noise". When i do that, It prompts me to specify the "output Port" and "input Port". Now I amstuck, since I have two output ports and two input ports. Therefore, without much knowing, I click on the "psin" port corresponding to "out+" and specify it as output port in do-noise. Similarly, I click on "psin" port corresponding to "In+" and specify it as "input port" in do-noise.

this is how the completed form looks like :
***********************************
Sweep Variable
(frequency highlighted)

Sweep range
(Start-Stop highlighted)
Start : 800M
Stop: 5G

Sweep Type
(linear selected)
Number of steps : 40

Do Noise
("yes" highlighted") and output and input ports specifiedas explained above.
*******************************************

Now when the simulation is run, I get this error :
"Error found by spectre at freq = 800 MHz during SP analysis `sp'.  'iprobe' or 'oprobe' did not appear in the first or the second entry in 'ports' parameter. Respecify 'ports' parameter and start again.

This is the problem and Any help is highly appreciated
Thankyou very much

Either that or use an ideal balun (there's one in rfLib) to do
a single <-> differential conversion.

Andrew.

Hi all,
When i placed only one "psin" port for each of differential input and output, I was able to get Noise figure graph from "sp" analysis.

But I have another question. We can also find noise figure using pnoise analysis. How will that be different from the noise figure found using sp analysis.  And for LNA, which simulation should i use, "sp" or "pnoise" ??

Thanks

Hello Ken,

While you said it is not suggested to use Pnoise to calcualte NF for LNA, why in SpctreRF user guide they have an example using Pnoise for NF in "simulating LNA"? what is their purpose for this example? Thanks.