[sdiy] THAT2162 vs SSM2164 (was Re: (re-)introduction)

[Neil Johnson]

Hi David,

> The 2164 is a current amplifier.

As is the THAT2162.

> It does not invert the current.  Positive
> current in gives positive current out, and negative current in gives
> negative current out.

In the true circuit-network form that actually describes an inverting
circuit since everything is described relative to the device.  But
that's not important right now.

> However, the 2164 must terminate at virtual ground,
> so the following I-V converter is always necessarily going to be an
> inverter.

Same as the THAT2162.

What THAT have done is arrange it so that common circuit application
-- audio fader -- has no phase inversion, which is very important in
mixing desk design.
ADI clearly had other motives for their choice of input/output relationship.
As in all things, there have been trade-offs in both designs.

Comparing the quoted performance, the THD of the 2162 is better than
for the 2164, but the noise performance is only slightly better
(within a dB or so), and there are tricks you can play to get the 2164
noise down further, but then you might as well use the 2162.  For
filters we have a sodding great integrating capacitor so noise is less
of a problem than distortion.

Cheers,
Neil
--
http://www.njohnson.co.uk