Bottom line up-front: don't do it.
First of all, what threat modeling have you done? In other words, if someone physically has the wallet (device) and they crack it open, the source of entropy is attackable (as it is an external circuit fed into the microcontroller). And most of these circuits have issues such as:
easily influenced or attacked via physical / evironmental attack (temp, voltage glitch, EMI, etc.)
aging. Many of these circuits have issues where after even only months, the entropy can drop by an order of magnitude.
Futhermore, it looks like (from the PDF you cited), not including NRE costs, the cost per unit is like 1.44 US dollars or so? At that is QTY 10K. Atmel (now Microchip) makes RNG chips (others too) that are totally validated, they resist physical attack (mesh), and they are like $0.50 in QTY 1 (see ATSHA204 as just one example). I think the Atmel chip drops to ~30 cents US in QTY 10K.
If you want to play around with this kind of circuit on your lab bench and in LTSPICE, fine, but if you're looking to do this is in a security product, there are better paths to choose.
Note: an MCU w/ built-in HRNG/TRNG is even harder to attack, although power/temp/glitch etc is still possible. But the attacker would have to de-cap the chip to tamper with the interface from RNG to microntroller's CPU.
