Hello.
BitfFury is deeply committed to a decentralized Bitcoin Blockchain ecosystem and we want to do all we can to ensure that as many hobbyists and engineers as possible have access to the technology we have developed with the support we've had from the Bitcoin community. Therefore we have decided to release our 28nm designs under Creative Commons Attribution Share Alike 3.0 License to give you the opportunity to get familiar with the style of our latest designs.
You will find higher resolution images together with schematics in
http://dl.bitfury.com/28nm/.
Let's take a look at the files:
12Vcircuit.pdf contains a circuit of a 12V StringPower hashboard. PCIe connector is used to interface with the motherboard. The connector has modified SPI interface with 2 data buses leading to chips. On the right side of the connector is the Level_norm level shifter cirquit which is there mostly for 55nm legacy purposes.
48Vcircuit.pdf contains a circuit of a 48V StringPower hashboard. Not much difference to 12V except longer strings for higher voltage.
StringPowerBlock.pdf is probably the most interesting one. This is a block of one 250nm communicator chip and seven 28nm chips. Here you can see how the individual blocks are interconnected (differential pairs), hashing chip connections and how the StringPower design that BitFury pioneered with our first 55nm chip works.
It's worth pointing out that the decoupling capacitors that you see around the hash chips and the 250nm communicator chip will be absent in the 16nm design. They have all been integrated. The only thing that will be required on the hash board apart from 16nm and 250nm chips will be 10pF 0402 capacitors for communication pins. So no semiconductors, electrolytes, stabiliziators, resistors etc will be needed. How's that for minimal BOM cost?
MbLiquid-9_v1.pdf This is one of our latest motherboard designs, that can accomodate 9 hash boards. As you can see we're using the releatively cheap PCIe connectors for connecting the hash boards.
This design is built around the STM32F407 that is being used as a commutator with UART input from any source (RasPi, USB-UART converter etc). The output is 9 SPI buses for connection of the hash boards. So from 1 UART connection we're able to service up to 1700 hash chips (over 20TH/s with our 28nm chip and even more with the 16nm). 16nm will work in a very similar way.
All-in-all the design is quite flexible when it comes to voltage. Every block is fed with 4-6V and is connectedto the outside through differential connections through small 10pF capacitors. Blocks can be connected in parallel or in series on one or several PCBs. The can also be connected directly to SPI of e.g. Raspberry Pi. They don't require stable voltage so no stabilisators or regulators are needed. The only downside of this design are the 6-12 I/O connections that take up some space on the PCB.
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quite a few blocks from Antpool/BITMAIN, where I have interests. Today you are even on top of the block finders. Great work! 
