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### Topic: 128-channel high speed digital pattern generator ~1MHz (Read 1 time)previous topic - next topic

#### mcpantsface

##### Oct 11, 2012, 06:20 pm
Greetings All,

I'm hoping you guys can give me some feedback on a project I'm working on.

So this is the worst-case: I'm trying to find/build a 128-channel high-speed (~1MHz) digital (5V 1's and 0's) pattern generator and I'm exploring possible solutions. The basic requirement is that I need to output 128 50/50 square-waves who's phases can be adjusted by small amounts. For example, the worst case the phase should be adjusted by 1/128 the period (1/1MHz/128 = 7.9us). I believe this means the clock rate of the system needs to extend to 128MHz.

So I see there being two basic challenges 1) How do I get 128-channel (i.e. 128-bit) parallel output and 2) How do I get the 1MHz clock rate with adjustable phase?

This seems beyond the capabilities of the standard Arduino but I'm trying to understand if a serial-to-parallel approach with a microcontroller would work. For example, if I took the 3 hardware timers on the arduino and connected shift registers to them, then each one could control ~43 channels at a max (ideal, but not feasible) frequency of 16MHz/43 = 372kHz. If I wanted to make the phase adjustable by 128th the period, then I think this would lower the max signal frequency to 372kHz/128 = 2.9KHz. So is this the right way to think about this or am I missing something?

Also what about other hardware solutions? The Maple Leaf clocks at 72MHz and has 4 hardware timers so that would mean 128channels/4 = 32 channels/timer, 72MHz/32 = 2.25MHz frequency reduced to 2.25MHz/128 = 17.6kHz with adjustable phase. Or what about the Beaglebone that tops out at 1GHz?

When I Google "high speed digital pattern generator" I get something like this http://www.byteparadigm.com/product-gp-24100-20.html or http://www.usbee.com/dx.html These are PCI or USB style devices, as anyone had some experience with this variety?

So can you guys help point me in the right direction or provide any feedback on this? I greatly appreciate any input.

Cheers.

#### dhenry

#1
##### Oct 11, 2012, 07:28 pm
Quote
provide any feedback on this?

What you are proposing is completely doable, just not with (solely) arduino;

So you can look into other hardware (fpga for example, or ram-based signal generator), or you can make your project more realistic, to a point where it is doable on arduino.

#### JoeN

#2
##### Oct 11, 2012, 09:51 pmLast Edit: Oct 11, 2012, 09:58 pm by JoeN Reason: 1
I had a similar question recently about generating signals from a high speed MCU where I assumed since the Arduino can generate 4Mhz square waves at 16Mhz that any MCU could generate signals at 4 instructions per.  It turns out not to be true at all.  14Mhz tops on a 700Mhz Raspberry Pi:

http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/

Unimpressive!

128 channels?  I am thinking FPGA too in this case, though I know not much about them other than the better ones are fast and have a lot of pins.  Maybe you can have the MCU program the pattern into RAM organized as 128 bits wide and have the FPGA fetch it 128 bits at a time and bang it out over the 128 output lines.  Probably you could run that a lot faster than 1Mhz and very accurately.  There is a lot of 10ns SRAM available and lots of FPGAs that can run at 100Mhz or better.   Have fun soldering a high-end BGA FPGA.
I will never ask you to do anything that I wouldn't do myself.

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