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Keeping specs secret is just part of the job. Getting a usable, working spec is another. We sat down with Jennie Grosslight to learn why JEDEC guards a spec, the basic DDR architecture, and geek out about the challenges of probing DDR.
Hosted by Daniel Bogdanoff and Mike Hoffman, EEs Talk Tech is a twice-monthly engineering podcast discussing tech trends and industry news from an electrical engineer’s perspective.
Agenda:
1:00
How are electrical engineering and protocol specifications defined?
2:00
Bigger companies tend to drive specifications because they can afford to put money into new products
Sometimes small or midsize companies with an idea can make something new happen, but they have to push it
2:50
Most memory technologies have a couple players:
1. The chipset and the memory controller industry
2. The actual devices that store data (DRAM)
3:30
There’s a tremendous amount of work between all the players to make all the parts work together.
5:00
Why JEDEC keeps information about new products private as they’re being developed:
If you spread your information too wide then you can get a lot of misinformation. Fake news!
Early discussions also might not resemble the end product
6:20
DDR5, LPDDR, and 3D silicon die stacking are new and exciting in memory
7:00
We keep pushing physics to new edges
7:20
Heat management in 3D silicon is a big challenge
8:20
LPDDR5 is the new low power memory for devices like cell phones and embedded devices
9:10
5G devices will likely depend on low power memory
10:20
Once the RF challenges of 5G are figured out there will be even more challenges on the digital side. Systems have to deal with large bandwidths and low latencies
11:10
Higher performance and lower power is driving development of LPDDR5
It will be interesting to see if improvements are made in jumps or very slowly
12:00
Dropping voltage swing and increasing speed both make the eye smaller
Making the eye smaller makes you more vulnerable to crosstalk
12:20 – Completely closed eyes for DDR5
13:00
How to probe DDR?
We use a lot of simulation because the circuits are so sensitive
14:20
Crosstalk is often a problem when making DDR and LPDDR measurements
14:50
Economics drives everything so new technology is often based on existing systems
15:40
What comes next is up to who comes up with the best idea
16:40
What will drive change is when the existing materials can no longer meet performance
17:50
Power is important for big data farms as well as cell phones
19:50
GDDR and DDR
21:00
Chipset rank on a DIMM
The pieces share a common data bus so you need to know the order to properly test
24:20
DIMM interposer used for logic measurements for servers
25:50
With a scope a ball grid array is used under a device or the pins are probed
Oscilloscope interposers are available that work similarly to the logic analyzer interposers
The logic analyzer looks at all the signals at once, typically the oscilloscope only looks at a few
28:10
When testing you want to validate that the device followed the protocal in the right sequence
29:10
Data rates of DDR
DDR5 is supposed to get to 6400 MT/s
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Many thanks for useful article, you helped me a lot.