_[sdiy]_ICL8038 worst ic off all time!

[Scott Gravenhorst]

Magnus Danielson <cfmd at bredband.net> wrote:
>From: Scott Gravenhorst <music.maker at gte.net>
>Subject: Re:_[sdiy]_ICL8038 worst ic off all time!
>Date: Mon, 08 Mar 2004 16:38:55 -0700
>Message-ID: <200403090038.i290ctg11008 at linux6.lan>
>
>> >> >There should be a list of "worst-IC-designs-of-all-time" it would 
>> >> >also be nice with a list of the most "neat" IC design of all time to!
>> >> >In the first list i would definitively put the 8038 and a bunch of
>> >> >early FM chips! In the second list i would put the 555, the 4046.
>> >> 
>> >> 555, I agree, in fact, I'd put that on the "worst IC of all time" list.
>> >> The 7555, however is fine.  I like the 4046 used as a PLL, I built a
>> >> frequency multiplying module with one.  The VCO basically sucks by
>> >> itself. 
>> >
>> >Hmm, i dont think the VCO sucks,as i remember, BJ showed once many years
>> >ago that you could build a remakable advanced VCO out of a 4046 IC! Well,
>> >at least a "very high frequency LFO" with sync and 4 quadrant modulation
>> >on the square, if im not remebering completely wrong, thats not bad for
>> >such a cheap and simple IC. Or one could use the HC version and do a
>> >nice DC to 30Mhz function generator. I say forget about the 8038! 
>> 
>> Looking at the spec, a 4046 is rated at 1.3 MHz, the 74HC4046 version runs
>> at max 17 MHz.  The VCO is fine, it's the current source that isn't very
>> good.  Check the TI docs, it has a whole section on the technicals of
>> the VCO.
>> 
>> I built up that circuit by Bjorn Nilsson(?) and couldn't
>> get it to track a linear CV.
>
>As I recall it, in the 4046 you have basically two inputs and one of them is
>really a current input, so that's your entry into the world. I did exchange
>emails with Björn Juhlin back then, and I don't recall exactly but I think I
>helped him with that particular part (I might have just caused confusion, since
>I was a little hasty to analyse things and made a few errors where he was
>right as I recall it).

Hmm, I'd still like to get this working.  Yes, you're right, one pin (12?) is a 
current sink pin.  I've designed a standard linear v-i converter that sinks to 
ground, but again, I think I was trying to run the current up too high.  The 
idea was to allow the v-i converter to control the current by setting the 4046 
VCO CV input to the positive rail (thereby opening it up full) and let the 
external sink do the work.  I'll have to try this again, but be more mindfull 
of the control current.

Something else I've wanted to try is to build the oscillator core from a 4007.  
The one thing that stopped me was that the reversing cap charge scheme would 
cause the cap voltage to go below Vss and that concerned me.  Then I re-read 
the data sheet stuff on the VCO and found that, by design, the cap is actually 
discharged through the protection diodes.  I'm thinking that I can do this with 
a 4007 as long as the diodes can withstand the discharge current (that means 
the cap should be as small as possible).  Using a 4007 this way, I could avoid 
the possible nonlinearity of the MOS current mirror that supplies cap charge 
current in the 4007.  It's a curiosity, I know I can make a saw VCO other ways, 
I just think the design is interesting.

>I haven't heard from Björn for several years now.

Yes, he did disappear.  Too bad.

>Cheers,
>Magnus
>

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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