Tool/software:
Hello all!
I am currently evaluating the OPA860 for an application where it would be configured as a common base amplifier and its noise performance is important.
Looking at the datasheet, I understand the noise specification I care about is the emitter noise current. Interestingly, in Fig. 23 of the datasheet I can see that this noise current increases for higher values of Radj, and thus that it decreases for higher bias currents.
I was surprised by this, as from what I understood from the internal structure of the OPA860 (from the datasheet as well as from section 2.3.6 of The Art Of Electronics), with its base grounded it would opperate basically as a complementary PNP and NPN common base circuit, where the classical tradeoff of Zin vs current noise would apply (i.e higher bias currents would mean higher gm would mean lower Zin but worse noise performance). Instead, it seems as with the OPA860 a lower input impedance and lower emitter current noise are achieved simulatenously!
Is this correct? If so, are there any tips anywhere how this is achieved? If not, what did I miss?
Thanks for any help!
Cai
