BJ's 4046 oscillator

[Magnus Danielson]

>>>>> "B" == BJ  <zzynt at swipnet.se> writes:

 >> Magnus Danielson wrote:
 >> >>
 >> >> Hi!
 >> >>
 >> >> It just truck me that there is more to BJs 4046 oscillator.
 >> >>
 >> >> >From the two buffer op-amps comes two waveforms that look like this
 >> >>
 >> >> 0 V -   ---   ---   ---   ---
 >> >> \  |  \  |  \  |  \  |
 >> >> \ |   \ |   \ |   \ |
 >> >> \|    \|    \|    \|
 >> >>
 >> >> 0V   ---   ---   ---   ---   -
 >> >> |  \  |  \  |  \  |  \  |
 >> >> |   \ |   \ |   \ |   \ |
 >> >> \|    \|    \|    \|    \|
 >> >>
 >> >> Adding them creates a saw, but subtracting them and you got yourself a
 >> >> triangle. Using the saw+square trick you can have a sawtooth of the
 >> >> same frequency as the triangle, and they are in phase. A deglitching
 >> >> is assumed ofcourse.
 >> >>
 >> >> Cheers,
 >> >> Magnus
 >> 
 B> Sorry, but the waves looks like this:
 >> 
 B> /|        /|        /
 B> / |       / |       /
 B> /  |      /  |      /
 B> 0V-----/   |-----/   |-----/
 >> 
 B> /|        /|        /|
 B> / |       / |       / |
 B> /  |      /  |      /  |
 B> 0V/   |-----/   |-----/   |-----

[Big fat hand slaming an obviuosly empty head...]

I was obviously tired when I wrote this, so sorry.

The point was that the spaced-saw waves where 180 degrees out of
phase, that I happend to get them in wrong polarity was due to a empty
and tired head.

 B> Therefore the final sawtoth wave is twice in
 B> frequecy of the sqare wave available at pin 3 .
 >> 
 B> A nother nice thing with this design is the ability to get PWM
 B> by the usage of the Xor gate.It generates 100% PWM, no need for
 B> external comparator.infact one can get PWM and Ring mod at the same time
 B> from the same Xor gate.
 >> 
 B> In wich way did you have in mind to do the saw to tri conversation?
 B> Im not so sure that you relly get a nice and clean tri wave due to the
 B> "out of phase" acting by each saw! If one would phase reverse one of the
 B> waves then you might get a tri! I have to try to see!

 B> BJ 
 B> again

Well, in the normal saw-to-tri case you would extract such a spaced
sawtooth that you then subtract with the saw (in a 1:2 mix) to get a
triangle. Here you allready got the spaced saws, so it is only
subtract these to each other.

Infact, the diff-voltage over the capacitor has a triangle shape, so
setting up an op-amp as a diff-amp (using the existing buffer amps in
BJs schematic) is a simple matter of a op-amp and a few resistors.

I even think that this might be a better solution than a normal
saw-to-tri converter.

I will try it out, I have all the stuff around.

Cheers,
Magnus