Cascode Amplifier...

[Rohit Chatterjee]

What is a cascode amplifier supposed to do???
I read it in a book that cascode changes the dc level of the input signal (say make the dc level zero) without attenuating the ac component....
On the other hnd its mentioned all over the net that it consists of CE amplifier followed by a CB stage...n is used to obtain good impedance match over a wideband...
Which is it really???

 

[crutschow]

A cascode stage is normally used at high (RF) frequencies to eliminate the miller capacitance effect between the transistor collector and base. The CB stage keeps the collector AC voltage of the CE stage near 0V so there is little AC negative feedback (feedback is undesirable) through the collector-base parasitic capacitance.

 

[Rohit Chatterjee]

So the part about cascode changing dc levels is wrong???I came across it in Schilling-Belove.....

 

[BrownOut]

That depends on the context. A cascode amp can change the DC level, but so do alot of amplifier configurations. The purpose of the cascode configuration, however, is to affect high gain at high frequency.

 

[Rohit Chatterjee]

Thats all i wanted 2 knw...thnx.....