4046 VCO experiment

[Hairy Harry]

Hi everybody:

Two thoughts

1) Check out the internal VCO schematic of the 4046... its in
ICAN-6101. Scott's circuit is still activating the CMOS Current
Mirror... so basically the operation is still the same.

2) Think about stealing the archetecture, but built with
discrete CMOS chips... maybe 4007 for the capacitor reset
section, and 4049UB for the rest... but absolute symmetry is
required... each branch must be formed from devices in the same
package. You need symmetry along the vertical axis...
(matched right/left hand). Then... replace the current mirror with a
discrete temp compensated current source.

H^)  harry


>From: Martin Czech <czech at Micronas.Com>
>Reply-To: Martin Czech <czech at Micronas.Com>
>To: chordman at earthlink.net
>CC: synth-diy at node12b53.a2000.nl
>Subject: Re: 4046 VCO experiment
>Date: Thu, 17 Aug 2000 09:38:03 +0200 (MET DST)
>
>The current source should be pretty linear but with some error at the
>low end. (Why not use a jfet precision current source?).
>
>I think the inner VCO circuitry is not published.  Linearity is not
>neccessary for most of the applications.  Who will demodulate FM with that
>chip anyway?  It seems to be fabricated in the very same CMOS process
>then anything else of this logic family.  So there are limitations on
>matching, mirrors etc. Certainly the internal integrator has low gain
>(but high bandwidth).
>
>Could you be more specific on the error?
>
>
>m.c.
>

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