In a cascode, the lower transistor is a common-emitter voltage to current converter. Its collector has a variable current, not a variable voltage so its Miller negative feedback is extremely low.
The upper transistor operates in the common-base mode so its base is grounded and stops negative feedback in the capacitance from its collector to its base from forming.
cascode
Posted - Apr 28 2009 : 7:57:36 PM
cascode.PNG