Quote:
Originally Posted by kalee20
The only way to double the gm of a transistor, that I know of, is to double the operating current (impossible in a series-connected cascode), or run the transistor at double the absolute temperature. You can't choose another type with a different gm (unlike valves). A cascode comprised of a BC107 and a 2N3055 will still display equal gm's and have the same signal voltage on the collector of the lower device as on the input. It's not a massive signal, but it's not rock-steady either!
|
Quite true, but it seems counter-intuitive to people not familiar with the Ebers and Moll equation and onwards. You could also change the Gm by having one transistor in a different material with a different band-gap. Can't think why I'd want to do this though.
If flat-out gain isn't required, emitter degeneration will artificially lower the Gm of the lower device only, and the swing at its collector will decrease (assuming Iq isn't changed) And the Miller pole moves up correspondingly.
David