Eeyore wrote:


Joerg wrote:


Eeyore wrote:

Joerg wrote:


And when it is on there will always be a remaining channel resistance,
commonly called Rdson. FETs aren't ideal switches. If, for example,
Rdson is around 200 ohms then you'll lose 1/5th of the signal.


J108 - 8 ohms typical.

Those seem to be kind of hard to get these days.


Really ? I bought 30 ex-stock from Farnell just a couple of months back. Not
*that* pricey either given the performance. About 25p each.


Digikey stock: Zilch. That's a red flag for me when I design stuff.
Pricing is even lower but what good does that do if I can't get any?



I doubt that the load needs to be as low as 1k either.


Yep, got to find a compromise between loss and leakage. However, with
T-switches leakage isn't such an issue.


That's for sure. It's the only way for very high performance. Mind you, single
jfets in series mode can do surprisingly well.


Yep, used them in samplers a lot. But not the J108 ;-)

BTW, do you know why the BF245 fell from grace? That's a mighty fine
device. The usual marketing bloopers?

--
Regards, Joerg

http://www.analogconsultants.com