Odp: [sdiy] inversion, CMOS, etc.

[gavin]

----------
>From: "Roman" <modular at go2.pl>
>To: "gavin" <elmystico at earthlink.net>, "synth" <synth-diy at dropmix.xs4all.nl>
>Subject: Odp: [sdiy] inversion, CMOS, etc.
>Date: Fri, Aug 2, 2002, 5:33 PM
>

>OTOH you say to
>leave the wave
>itact and cut the lower peeks, so you simply need
>a resistor and a diode
>to ground.

Pardon my possible ignorance here, as I understand it I would actually need
a diode in series and a small resistor to ground to make a small half-wave
rectifier, so that the positive peak would pass through the diode and the
negative peak would be blocked by the diode and bled off through the
resistor to GND.  Maybe that's not how it works and if so I'd like to know
how it does work because then I'm operating on wrong info about how diodes
work.
This is what I imagine the half wave rectifier to look like.

     +5V/-5V   ---|---D|------   +5V/0V
                  |           
                  R
                  |
                 GND

  
What I'd like to do is combine the HW rectifier with the passive summer to
create a pot crontolled sort of "sunrise" effect of the wave going up and
down the "horizon" of the ground line (sorry for the "metaphysical imagery,
I knew my interest in analog synthesis and those high school LSD experiments
had something to do with each other...)

Something like this:

/\__/\__/\__/\__/\   pot turned all the way down, +5V peak


/\  /\  /\  /\  /\
__\/__\/__\/__\/__\  pot turned all the way up, +10V

i'd like to make this function voltage controllable also, by adding another
summer between the signal and the input from an LFO or other LF voltage
source.  The thing I'm wondering about is if for ultra high frequencies (RF
type) do I need a special high speed diode for the rectifier or will a
1N4148 type do the job?