[sdiy] Sic Transit OTA Mundi

[James Patchell]

I hope you get a better answer than I did...

At 01:54 AM 5/26/2005 -0700, Don Tillman wrote:
>    > Date: Fri, 20 May 2005 06:09:15 -0400 (EDT)
>    > From: The Old Crow <oldcrow at oldcrows.net>
>    >
>    >   Something I've always feared has come to pass:
>    >
>    > http://www.intersil.com/cda/deviceinfo/0,1477,CA3280,00.html
>    >
>    >   "To be discontinued"
>
>Here's a copy of the message I just sent to Intersil support:
>
>   -- Don
>
>----------------------------------------------------------------
>
>Gentlemen,
>
>I see from the Intersil web site that the CA3280 and CA3280A
>Tranconductance Amplifiers have been scheduled to be discontinued.  I
>want to suggest that these chips are too important to retire.
>
>   1. The RCA/GE/Harris/Intersil line of Operatational Transconductance
>      Amplifiers used to include the following chips:
>
>        CA3080 -- basic single OTA, used for most examples of OTA
>        operation and applications
>
>        CA3060 -- triple OTA
>
>        CA3094 -- OTA with simple output buffer
>
>        CA3280 -- dual deluxe OTA
>
>      The CA3080 was discontinued recently, the CA3060 and CA3094 were
>      discontinued previously.  So right now, the CA3280 is the last of
>      of the Intersil OTA's.
>
>      The 3280 is clearly the most advanced and flexible.  It features
>      a very nice input diode linearization circuit, low noise, low
>      offset voltage, and it comes in matched pairs.  None of the other
>      chips comes close in these areas, so if you can only support one
>      OTA chip, that's the one.
>
>      The 3280 is also capable of functionally replacing any of the
>      other OTA models, ignoring the obvious pin-compatibility issues.
>
>      There are not many alternatives available from other
>      manufacturers.  For instance:
>
>        LM13600 -- dual OTA with simple diode linearization and simple
>        buffer
>
>        LM13700 -- ditto
>
>      The LM13600 has been discontinued.  Neither the LM13600 nor the
>      LM13700 has the performance of the CA3280.
>
>
>    2. There are many audio electronics applications for the 3280, and
>       while admitedly most audio is digital now, the analog
>       alternatives are where the high-end markets lie.
>       ("Reproduction" is mostly digital, put "production" is mostly
>       analog.)
>
>    3. The 3280 is invaluable in electronic music work.  It's the
>       preferred chip for voltage controlled oscillators, voltage
>       controlled filters, voltage controlled amplifiers, waveform
>       shaping, modulation, signal processing, routing and control,
>       chaos circuits, simulation of mechanical systems, and so forth.
>       And there is currently a resurgance in modular analog music
>       synthesizers (SynthTech, Synthesizers.com, Buchla, Cyndustries,
>       Blacet, Doepfor, Oakley, etc.).
>
>    4. Along those lines, the 3280 is inspirational for new designs.
>       For example, my Quadrature Trapezoid thru-Zero Voltage Control
>       Oscillator, my Interpolating Scanner and my Voltage Controlled
>       Duty Cycle Sawtooth Circuit (http://www.till.com/articles) are
>       all innovative designs inspired by the CA3280.  And I have a
>       significant number of additional applications in the pipeline.
>
>    5. I predict that if the CA3280 is not discontinued, sales will
>       pick up as the supplies of the other OTA chips drop off and the
>       choice of which OTA to use narrows, with the resurgance of audio
>       and electronic music applications, and with new applications
>       being developed.
>
>In summary, I think it would be a big win to keep the CA3280 in
>production, for all the standard business reasons, but also because
>the chip is culturally and educationally important, and it would give
>Intersil a great repuation.
>
>Thanks for listening.
>
>   -- Don Tillman
>      Engineer, consultant, writer, musician
>      Palo Alto, CA
>      don at till.com
>      http://www.till.com
>
>----------------------------------------------------------------

         -Jim
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