Yamaha CS80

Ensoniq came up with patented technology to build poly AT into non- 
weighted keyboards at apparently very little extra cost so most of  
their unweighted keyboards starting with the EPS family had it (EPS,  
VFX, ASR, SQ, TS series as far as I know).  They made some weighted  
keyboards and none I know had it.

Fatar built all of them for Ensoniq, but since it was Ensoniq's  
patent, business ethics or contract probably kept Fatar from  
developing rival technology to do it cheaply another way. In other  
words poly AT was not under patent but the only low cost way to do it  
was. Fatar BTW built the bulk of keyboards for everyone in the 80s  
and 90s (other than Roland, Yamaha and some non-synth manufacturers)  
and only built it for Ensoniq. So I would guess when the Chinese got  
into synth keyboard manufacture big time this decade it was a feature  
than no one had used in a while and wasn't on the list of specs they  
needed to offer.

Roland had their weighted 88 key A-80 in the late 80s as well as one  
of the few unweighted non-ensoniq keys, the 76 key A-50. Their  
replacement master keyboard  model was the A-90 with the simulated  
poly AT that was mentioned on the list. I've not used it but no one  
says it's as good as the real thing and Roland didn't offer it again  
afaik