Been quite a few years since I last dug in the subject, but from what I remember, Sony used for the PS1 an emulator called "POPS", and Sony up to the Vita added hardware from the previous generation into the new console, but I don't remember any mentions of them adding hardware further than a single generation.

And a surprise to me, but apparently according to this wiki (cw: Fandom), the PS3 used some degree of emulation even for the PS2. Rather curious as to run PS2 games, the PS3 boots into a PS2 mode, which feels almost like a dual boot.