[sdiy] Discrete OTA

[Tom Wiltshire]

> http://www.johnhardyco.com/990OpAmpDetails.html


Fascinating paper. Thanks, Neil.

It makes a good case that I shouldn't be thinking about trying to get it all on one package anyway, since the performance will be much improved by doing it with discrete parts, if done carefully. So perhaps this world of little SMD modules like discrete OTAs or discrete XYZs is a good thing.
It's still tough to take though, for someone who grew up with SSM synth chips in the Maplin catalogue! I long for those days!

T.

On 1 Apr 2014, at 16:14, Neil Johnson <neil.johnson71 at gmail.com> wrote:

> Tom Wiltshire wrote:
>> Is it possible to integrate circuits at the pre-packaging level? Could you get a load of unpackaged 2164s and a load of op-amps (say, a couple of duals) and then put the three little tiny wafers into one package? The lead wires would link up the power pins of each, and the rest would go straight out to the IC pins.
>> Seems to me that if such a thing were possible, it'd be much cheaper than designing custom silicon. Just use existing silicon and stick it in the same lump of plastic.
> 
> A single package would need a custom leadframe to hold the two chips
> and provide bondouts to pins.  As well as the packaging you would need
> to be able to buy the bare die.  ADI are out of the game, not sure if
> CoolAudio would be happy with that arrangement?  Same for THAT Corp.
> Unless you wanted to buy very large quantities.
> 
> Next option is an MCM (multi chip module).  Bare die on a ceramic substrate.
> 
> The cheapest option would be a thick film hybrid if you can't get the
> bare die.  Opamps come in really tiny CSP packages, so the 2164 or
> 2162 would be the limiting factor.
> 
> After that you're down to traditional fibreglass PCB module in some
> sort of encapsulant.  The world of discrete op-amps offers some useful
> background.  The John Hardy 990 op-amp provides an interesting
> comparison:
> 
> http://www.johnhardyco.com/990OpAmpDetails.html
> 
> Worth reading the PDF - it includes the schematic of the internal
> circuit, so nothing to hide there.  Supports Olivier's comments
> earlier.
> 
> Neil
> --
> http://www.njohnson.co.uk