high freq vco

Magnus Danielson cfmd at swipnet.se
Tue Aug 15 02:38:48 CEST 2000

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


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.


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