a question about ADS

In ADS,The transistor with S parameter named SP but i did the design with the transistor with package ,but their results are not the same!
why?
thx

Do you mean you drag the "SP" from ADS component library?

The S-Parameters of a transistor naked die are always different than packaged version due to parasitic effects such as bonding, capacitive effect of the diepad , etc..
Therefore s-parameters seem to be different.
In the databooks, s-parameters are given usually for packaged version unless noticed.

yes!can you tell the reason?

The explanation from BigBoss: "The S-Parameters of a transistor naked die are always different than packaged version due to parasitic effects such as bonding, capacitive effect of the die pad , etc.." is true and correct.

To know more about this effect on the S-parameter, you can refer to 0302M34.pdf for the parasitic effect at http://www.elektroda.pl/eboard/ftopic65524.html

To start our design we can pick transistor from s-parameter lib or from pakage lib which option is good and why?

i think it is better to us SP models , it is easier to do s parameter simulation with them , without need to design bias networks in the frist design stages ,
begin with stabilty and matching to get the gain and the desierd NF ,
after u design matching networks
use nonlinear model to get the DC point u used in sp
and then design the bais netowrk

Care:
The s parameter can obtain from the DATA sheet or the EDA soft lib.And mean the linear lib.
For the BJT,there are two type of you must be care to use it.One is the chip and it do not include the pakage model ,the other is the pakage DATA.

The other you must care is the reference plane for the S dembed.You must use the same reference plan to design.

Just this.

In nomal,the simulated result do not meet the test data very well. Because some thing you may do not consider:such as the coax to microstrip transition/the coax you used to link the test equipment an so on.

If more exact,you may use nonlinear simulate.