DDR desing with FPGA

Hi

I hope someone has more experience and can give advice -

what I need (for urgent customer design) is simple? design with FPGA having high speed video memory (must be implemented with standard cheap devices like DDR) - the constraints are both PCB size and power consumption. The system must support sustained 12bit DDR datastream at 165MHz pixelclock to the DVI encoder.

so current consideration is FPGA: V4 + Memory: 2 fully separate DDR chips BGA144, 32 bit physical eg 64 bit per clock edge

Q: as the DDR chips are mounted VERY close, all wires less than 0.5 inch? and there is never more than one load on the DDR chips, I am wondering is it safe to not have DDR termination resistors by using DCI in the FPGA and switching the DDR into SSTL1 mode by the extended mode register write?

Q: or perhaps there is some other memory solution known, that doesnt require more PCB space and is not much more expensive. ZBTRAMs are in BGA also and there are special video rams, but those are usually way more expensive and/or more exotic.

I guess main issues are correct PCB design and decoupling as the DDR chips power consumption is per datasheet 0.8A and the FPGA is running at relativly high frequencies as well.

any help/hints appreciated

Antti

Reply to
Antti Lukats
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Hi Antti,

yes you are of course correct : PCB design and decoupling is the main issue. If possible, simulate your layout. If not possible : follow standard design practice (correct layer-stackup to start with, impedance matched lines,etc...) and you should be safe. I have a design with V4 and 6 DDR2 memories running at 200 MHz, the longest traces are about 2 inches. DDR2 has the possibility of internal termination, V4 has DCI. I disabled DCI on the DQ bus (so only DCI on the strobes are enabled) because of power consumption and the memory-interface still works => DQ bus shows some moderate under/overshoot, but still nothing worrying. Oh and by the way : I also use it as video-memory.

hope this helps...

Bart De Zwaef

Reply to
zeeman_be

"zeeman_be" schrieb im Newsbeitrag news: snipped-for-privacy@g43g2000cwa.googlegroups.com...

thanks! DDR2 looks better, just need to find a chipd with 32 bit wide bus, micron has only x16 chips available :(

antti

Reply to
Antti Lukats

Which FPGA are you going to use ? IP-Core or own controller ?

Rgds Andr=E9

Reply to
ALuPin

schrieb im Newsbeitrag news: snipped-for-privacy@g43g2000cwa.googlegroups.com... Which FPGA are you going to use ? IP-Core or own controller ?

Rgds André

V4LX, DDR2 chips that decided already IP core we might to roll our own at the end

antti

Reply to
Antti Lukats

it

Antti, If the risetime is six times the flight time of the traces, you'll probably be safe without terminations. Risetime 1ns => 1 inch trace length in FR4. (25.4mm for metric Estonians! Actually, are Estonians metric?) Trace length must, of course, include the bond wires, bga traces, lead frames. Cheers, Syms.

Reply to
Symon

Teo, have you tried the IP core from Lattice ? Or are you using the datapath template from the IP Manager ?

Rgds Andr=E9

Reply to
ALuPin

We are using the IP core from Lattice that imports to the IP manager. My consultant has it running in an EC20.

Reply to
Teo

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