Hi,


I haven't worked with SiGe, but since you have NPN transistors, I guess your gm/IDS is 1/Vt =40. So if you have 10 mA, you should get gm of 0.4 and if you use this to directly drive your load you should be able to achieve a conversion gain somewhere close to 40 = 26 dB. Since this is more than enough, you can even use some resistive degeneration to improve the linearity. The NF seems to be a given for that power consumption but again, i haven't worked in SiGe.

You could add a buffer stage but I guess it would need most of the 10 mA budget in order to drive the 100 ohm load and therefore your NF would degrade. The advantage would be better reverse isolation and you could make your conversion gain independent of the load impedance. My last comment is that if you do put most of the power into the buffer stage, you might have to worry about the IF bandwidth achievable by the actual mixer stage.

Anyway although i haven't worked with SiGe, most of the specs seem achievable. Hope it helps,


Aaron

0.35 SiGe? Probably IBM (6HP) or Jazz....

Suggest looking into lowering the impedance of the mixer and using that (unbuffered) to drive the SAW directly.

Why?
Lower impedance equals less noise,  better linearity from higher current and fewer active amplifiers in the system.

If that doesnt fly, you will need to pay the penalty for a buffer amplifier. Emitter followers are lots better at HF than Source followers but still some questions on zero db gain (actually a little loss) and additive noise, linearity issues, and all that.