[sdiy] Sic Transit OTA Mundi

[Don Tillman]

   > 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

----------------------------------------------------------------