Adding external DC supply to increase supply voltage

[Foisal Ahmed]

Hi everyone,

I am using Basys3 Board of the FPGA chipArtix-7, XC7A35T-ICPG236C.  How can I  increase / change the core voltage of the FPGA to accelerate any operation?  The nominal core voltage is around 1.1V. If possible plz. show it graphically. Thanks in advance.

Regards,

Foisal

[JColvin]

Hi @Foisal Ahmed,

I would not change the core voltage of the FPGA (and it's not readily possible to do with Digilent boards anyway as they are already connected to their respective power supplies as you can see in it's schematic: https://reference.digilentinc.com/_media/reference/programmable-logic/basys-3/basys-3_sch.pdf). You do not want to increase the voltage beyond 1.1V anyway as that would exceed the maximum internal supply voltage listed DC and AC Switching Characteristics datasheet for the Artix-7 FPGAs (DS181 from Xilinx).

In grand scheme of things (not limited to FPGAs), you usually want to use smaller voltages rather than larger ones for faster I/O operation as the corresponding slew rates will be inherently quicker, effectively increasing the theoretical maximum speed.

If you want to increase the speed of your application, I would instead recommend increasing your clock speed and doing all the needed adjustments, optimizations, and simulations with your design to ensure it operates as intended at that frequency.

Thanks,
JColvin

[Foisal Ahmed]

Dear JColvin,

Thank you for your nice explanation.

Actually, i do not want to increase the speed of the operation. Instead, I like to want vary the supply voltage  below 1.1V by using externally DC supply voltage. Some, research using Spartan-3A FPGAs in Numato Lab FPGA development boards (https://numato.com/product/elbert-v2-spartan-3a-fpga-development-board) where they vary input supply voltages from 1.1V to 1.40V. I just want whether it is possible  or not of doing this type of things using my Basys3 board.

Best regards,

Foisal

[zygot]

On 5/8/2020 at 4:35 PM, Foisal Ahmed said:

How can I  increase / change the core voltage of the FPGA to accelerate any operation?

Further on you say that you want to lower Vccint.

Before you start thinking about making changes to a particular board for experimentation it might be a good idea to do your homework. A good place to start would be DS181 as @JColvin  mentioned. The very first paragraph might help help you decide if your experimentation is worth the effort. Then start looking at the AC switching specifications.

A better approach might be to buy a board with a higher speed grade.

It's not clear what you mean by "accelerate any operation". Are you thinking that perhaps you can beat Xilinx at its own screening/pricing game? Are you trying to make a poor design meet project specifications without changing the bitstream?  The recommended Vccint range allows for 5% or less variation.

If you have a board that allows for varying Vccint then use that, though I'm not sure what inferences can be applied to a very different family and process. If there is a compelling reason the best approach would be to make your own FPGA board specifically designed to manipulate your variables and measure your metrics.

[Foisal Ahmed]

Hi everyone,

Regarding the above post i need some other queries. Basys3 board has option to use external power supply changing JP2 jumper and externally using J6 port 5V dc can be supplied. The range of extrenal voltage is 3.6V to 5.V. According to the basys3 manual regulator circuit (IC10: LTC3633) is used to provide 1V for FPGA core. My question is that if I varied this external supply voltage in the basys3 board, whether the core voltage (1V) of FPGA is chaged or not. For example, If the external supply voltage of the board is changed to 4V , what will be core voltage of FPGA?

Thanks in advance.

Foisal

[elodg]

The internal voltages are regulated to their nominal values for the whole 3.6 - 5 V external voltage. In other words, changing the external voltage does not change internal voltage rails.

The Basys3 does not have an option neither for tuning the internal voltages, nor for providing internal voltage rails from external power supplies.

Some high-end boards like the SUME has this option tuning option: https://reference.digilentinc.com/reference/programmable-logic/netfpga-sume/reference-manual

[Foisal Ahmed]

Dear elodg,

Thanks a lot. This is the answer what was I actually anticipated. One more question @elodg, what is definition of nominal voltage/ values? Thanks in advance.

Regards,

Foisal

[elodg]

You will have to do the work yourself. Take the schematic https://reference.digilentinc.com/learn/documentation/schematics/basys-3-schematic , follow the voltage rails to ALL their loads and look up the operating ranges in  the load's datasheet. For example, the FPGA's is linked in the Basys 3 reference manual: https://www.xilinx.com/support/documentation/data_sheets/ds181_Artix_7_Data_Sheet.pdf.