[sdiy] Filter Structure Question

[Scott Gravenhorst]

Yeah, I know it looks strange, but there's no connection between that ground
and any power supply common.  That "floating" inverter isn't really unused.
 It creates a signal ground approximately halfway between the 4069UB Vss and
Vdd pins.  If a symmetrical CMOS inverter has it's input connected to it's
output, the output seeks a voltage approximately halfway between the Vss and
Vdd pins.  It creates a center reference between the IC power rails which is
why it is used as a signal ground.  In this case, the ground point sits
about 2.5 volts away from either rail (which are at 0volts and 5volts). 
This was a suggestion from Magnus to avoid problems with the virtual ground
of the summing nodes created by the integrators.  Doing this allows me to
reference my CV signal to that ground so that it properly influences the
gate of the MOSFET feeding current to the integrator.  Magnus's last comment
was that I was "bloody close", so there still may be something I don't yet
understand.  I didn't really understand his comment about using a dual
supply, I don't know what that would be necessary.  I'm going to throw this
at a solderless bread board tomorrow and see what happens.  Maybe I'll find
out...

"Jay Schwichtenberg" <jays at aracnet.com> wrote:
>Scott,
>
>Is there a reason that you gounded the output of the unused inverter in the
>schematic?
>
>That along with the fact the input and output are tied together scare me.
>
>Good luck with the design.
>Jay
>
>> -----Original Message-----
>> From: owner-synth-diy at dropmix.xs4all.nl
>> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Scott Gravenhorst
>> Sent: Friday, July 16, 2004 12:16 PM
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: Re: [sdiy] Filter Structure Question
>>
>>
>> Pictures being worth many more than a thousands words, here is
>> what I have envisioned:
>>
>> http://home1.gte.net/res0658s/CMOS_SVFb.gif
>>
>> The 4007 power pins are both open.  All of the inverters come
>> from the same 4069UB
>> package.  The ground symbol is the signal and CV ground, whereas
>> the 0volts and
>> 5volts terminals are just the regulator outputs.  0volts is not
>> connected to
>> ground.  Resistor values are SWAGs (SWAG = scientific wild ass
>> guess).  From what I
>> read below, you would suggest 100 ohm as a SWAG for each power
>> supply feed resistor.
>>
>> Am I close?  Or are you talking about a more specialized power
>> supply system?
>>
>
>

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