high freq vco

Hairy Harry paia2720 at hotmail.com
Tue Aug 15 16:09:19 CEST 2000


BJ's schematic was to generate a sawtooth wave from
the 4046... not a triangle. It had two high impedance
buffers looking at either side of the timing cap.

I think the principle of VCO operation includes charging the
cap in  both directions... so grounding one end would not
work IMHO (but what do I know ???)

H^)  harry

I've noticed that since time began... everyone has wished the
4046 was more than it is...
:^)


>From: Magnus Danielson <cfmd at swipnet.se>
>To: augustopinoche at hotmail.com
>CC: synth-diy at node12b53.a2000.nl
>Subject: Re: high freq vco
>Date: Tue, 15 Aug 2000 02:38:48 +0200
>
>From: "Augusto Pinoche" <augustopinoche at hotmail.com>
>Subject: Re: high freq vco
>Date: Mon, 14 Aug 2000 23:12:59 GMT
>
> >
> > > > No its not, the oscillator core is current controlled,
> > > > in fact its a form of multivibrator.
> > > > It sincs current from a current source/mirror.
> > > > One side looks like a Triangle osc's charge and
> > > > discharge part, two fets open and closing.
> >
> > >You usually don't see this in the datasheet, but there are things like
> > >appnotes ;D
> >
> > You "do" se this in datasheets if its contains this
> > type of information, appnotes seldom show this type
> > of info.
>
>I am actually refering specifically to the case of the RCA Databook and 
>what is
>described by the datasheet and what is being described by the application 
>note.
>It seems that all 4046 datasheets have inherited from the same source and 
>in
>this source there is no more detailed look. In the RCA Application Note
>ICAN-6101 "The RCA COS/MOS Phase-Locked-Loop A Versatile Building Block for
>Micro-Power Digital and Analog Applications" will Fig.8 disclose the VCO
>section in sufficient detail to understand what it does.
>
> > > > You can use BJ's idea to do a triangle OSC but my
> > > > idea here is why not ty the cap from pin 6 and to gnd
> > > > and pin 7 truh a 10k resistor to +V to get a triangle osc?
> > > > (wonder if i got that right?)
> > >
> > >There's a thougth. There is only one way to know - try it!
> > >Drop in a suitable resistor in series with the cap and you have the 
> >high
> > >end compensation...
> >
> > And then you change the frequency as well.
>
>Well, that IS the point of a high end compensation, it will change the
>frequency enougth to compensate for any reset time. The 4046 reset time is
>however less than that of a typical sawtooth generator.
>
> > >Oh, I did not find BJ's site anymore, I was just about to take a peek 
> >at
> > >the 4046 based VCO there... Swipnet seems to finally pulled the plug on 
>it.
> >
> > His page is at:
> > www.home.swipnet.se/~w-133242
>
>Eh, it's more like
>
>http://home.swipnet.se/~w-133242
>
>and I was refering to his old site (diffrent URL) where that schematic 
>actually
>did exist where as the current site does not hold it (visible).
>
> > For some resaons?
> >
> > >But naturally you have the schematic, don't you ;D
> >
> > No!
>
>If I recall correctly he had two op-amps buffering from each end of the VCO
>core capacitor and then that output was mixed in a third op-amp to output 
>the
>triangle waveform.
>
> > > > Just hook on a expo converter to pin 11 and VCO you go!
> > > > Use the CV input as a lin FM input, or shall we say PM
> > > > input folks?
> > >
> > >Um, I think the expo should hit pin 12, not pin 11. Pin 11 shoule be 
> >N.C.
> > >or possibly wired to pin 12 just to keep that MOSFET out of buissness.
> >
> > Depends on what you want to do actually!
>
>Well, yes. But it was assumed that this particular FET was to be blamed for
>some of the lack of range and traceabillity.
>
>Cheers,
>Magnus

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