[sdiy] question on JFETS in vco of MS series

[Magnus Danielson]

On 27/08/11 20:24, Ian Fritz wrote:
> At 10:40 AM 8/27/2011, Dave Manley wrote:
>
>
>> http://en.wikipedia.org/wiki/Cascode
>
> Exactly. I believe in this case the purpose of the cascode is to
> eliminate the Early effect, which isn't emphasized in the wiki.
>
> This is one of the big advantages of the Terry Michaels design (EN#62,
> ENS-76, etc.); the expo source drives a virtual ground so there is no
> Early effect.

Similarly the current buffer in a cascode setup is used to de-couple the 
Miller capacitor (between collector and base) which would cause 
slew-rate limiting, but the current buffer lets the collector see much 
smaller voltage shift and then the feedback capacitor has less voltage 
to act on and the current gain can be better utilized at higher frequencies.

Regardless, the same method works to avoid the early effect.

Cheers,
Magnus