On Mon, 07 Mar 2011 13:59:44 -0800, Tim Wescott
wrote:

On 03/07/2011 11:20 AM, Jim Thompson wrote:
An XOR is a convenient structure to allow a control signal to invert
or non-invert another signal.

Trouble is (as classically done) inverting has 3 stage delays, while
non-inverting has only 2.

Anyone know of a configuration that has symmetric delays?

Thanks!

(I'm rolling my own at the device level so anything goes :-)

I vaguely remember seeing a picture of this done at the transistor
level, in CMOS, with a structure reminiscent of a trimmed-down Gilbert
cell mixer.

But I'm not sure if I could give the actual circuit if my life depended
on it.

At least in the 1970's ECL 10000 gate the basic logical element was
the OR/NOR gate consisting of an differential amplifier followed by
emitter followers.

The ECL 10K Excusive-OR gate was implemented by a cascaded Gilbert
differential stage followed by level shifters,