[sdiy] MOSFET ANGST

[Scott Gravenhorst]

Ok, I see what you mean with the P transistor needing an inverted version of the
CV, however, the gates of each inverter of a 4007 are internally tied together,
so we cannot drive them separately (wish in one hand...).  

So either discrete MOSFETs are needed or we can use an N from one inverter and a
P from the other, however this requires 2 4007s for the filter.

The question is: Will doing the parallel P & N help anything?  Or can I just
forget the P transistor and use the N transistors alone?






Magnus Danielson <cfmd at bredband.net> wrote:
>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!).


Digital error (fingers are digits...)  Meant 4069UB, not 4046...


>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
>

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