X, SSM2142, and voltage feedback?

[Axon]

I've been reading some of Jung's stuff from Op-Amp Applications and he mentions the SSM2142 as having a "cross-coupled Howland circuit" that allows either balanced output to be referenced without loss of quality.

I'm also reading up on the whole X thing on the forums, and how it is inherently current-oriented in nature - voltage feedback schemes like ie in most opamps cannot be used in the basic design.

However, to my untrained eyes, the effect cross-coupled Howland circuit sounds suspiciously like what is being accomlished with a supersymmetric circuit. More specifically: if a voltage arises on the 2142 output that is uncorrelated with the inputs - whether due to output grounding, or amplifier noise, or whatever - it is fed back into the other amplifier, and effectively becomes a common mode signal. For the 2142, the cross-coupled feedback is accomplished through sense outputs which lay beyond some 50 ohm output resistors and load caps, but I see no reason why the feedback path could be moved to before the output resistors - so that the feedback signal is effectively reading the amplifier distortion instead of the line distortion.

Isn't that exactly what an X circuit does, except in the current domain? In other words, is a cross-coupled Howland circuit a voltage-domain analogue of supersymmetry?

[Axon]

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