[sdiy] MOSFET ANGST

[Magnus Danielson]

From: Scott Gravenhorst <music.maker at gte.net>
Subject: Re: [sdiy] MOSFET ANGST
Date: Sat, 17 Jul 2004 18:08:23 -0700
Message-ID: <200407180108.i6I18NZ25841 at linux6.lan>

> Many thanks.  (*slap*, I needed that!)
> 
> Well, dang, I knew this and STOOPIDLY didn't apply it (he says as the palm of
> the hand smacks the forehead).  Looks like I need those silly resistors to do
> the drain to gate feedback deal.  I will test that next.

Actually, you needed to learn about that extra relationship. You tried, it
behaved ugly and you asked for additional wisdom. Now you hopefully have 
learned your lesson and can go on. 

> So my other question is why do some applications such as hex voltage
> controlled mixer using 4046UB (or 4049UB) connect pin 14 to pin 7?  Other
> than static defense, I see no purpose in this because it appears that the P
> transistors don't do anything.  In fact, AN105 shows a voltage controlled
> attenuator with a single FET, yet it's input is AC.  Am I, therefore, not
> hallucinating that nothing is changes when I connect the P transistor?

I assume you meant 4069UB and not the 4046 (which I *do* have a few around 
here in my summerhouse... they just came with me by accident!).

I think I already addressed this in my previous post. The point is correct
that the P transistor does not really do much normally, it needs to be driven 
with an inversed signal. However, this is easilly done and away you go!

Just use the 6th inverter of your 4069UB for the CV inversion and you should
approximate happiness a little quicker.

Cheers,
Magnus