As part of my university education I had to build a decent project, so when I saw the oportunity to actually design a working chip, I just couldn't resist. It turned out that I was the only student that applied for that project. :D
The general idea was to have multiple "convoluted" oscillators that would produce a long periodic function each with a different output that would be xor-ed and shifted in a linear feedback shift register, and eventually shifted out as a byte.
Of course that long periodic function isn't really so periodic, since it has a lot of jitter, and that is the reason why this device will never run out of entropy.
I first soldered a 4000 series prototype that was just a proof that my concept work and the prototype generates ~12000 random bytes per second @ 5V, and ~24k @ 12V.
Since the 4000 series logic is ran at its maximum frequency, it is the first time that I saw 4000 logic chips that got warm to the touch.
This project was on display on the mini maker fare in Trieste 17.5.2014. The device was connected to a FTDI FT245 USB interface to a PC which had a demonstration program written in Java. The program can be downloaded here, and it includes a live chart, which is slowed down 200x times (by xor-ing 200 points in a single point) and a FFT spectrum plot which shows the spectrum of the generated random values.