"A Lack of Clarity Could Put the Brakes on Any Journey to Success"

I'm not a big fan of the J-school approach to writing an article where you start with some anecdote that has nothing to do with what you are going to write about. Most articles like that are best started on the second page. But I did like author Steve Maraboli's quote that I made the title of this post. Plus, I really am going to write about Clarity. In fact, I already did. In my post Bringing Clarity of Signal to High-Performance Connector Design, I said that I'd been working on a white paper about 112G signal integrity. That post focused on how connectors are designed, which turned out to be more interesting than I had expected. But most people are not going to design their own connectors, they are simply going to select the connectors they need and use them in their system. That is the main focus of the new white paper Overcoming Signal Integrity Challenges of 112G Connections. It is now published, and I'll put a link to it at the end of this post.

I'm obviously not going to put the whole white paper in this post, but I will tease you with the abstract:

One of the big challenges with 112G SerDes (and, to a lesser extent, all SerDes) is handling signal integrity issues. In the worst case of a long-reach application, the signal starts at the transmitter on one chip, goes from the chip to the package, across a trace on a PCB, through a connector, then a cable or backplane, another connector, another PCB trace, another package, and arrives at the receiver. By the time it arrives, the signal is very distorted, making it a challenge to recover the clock and data-bits of the information being transferred.

This white paper looks at how to handle these signal integrity issues and ensure that data is faithfully transmitted with a very low bit error rate (BER). The focus will be on 112G long reach. Many similar considerations apply to shorter reach, and to 56G (and lower data rates), but in some sense, 112G long reach is the most challenging case. While this white paper does not cover the actual design of 112G SerDes silicon, it does consider how connectors are designed.

One reason for not covering the actual design of 112G SerDes silicon is that you are not going to design that block yourself. If you didn't start to do it a couple of years ago then you are too late. And do you really want to put a testchip on the critical path for your SoC design? You are going to license IP if you are designing an SoC that needs 112G SerDes I/Os.

Another reason is that you might not be designing a chip at all. You might just be building a board-level system and putting a few chips on your board that communicate using 112G. But you still need to worry about signal integrity. At one level you need to characterize the drivers, channel, and receivers to do signal integrity analysis. But that already assumes that your channel is good enough to make this possible. If, for example, your return loss is too high from a connector, then not enough of the transmitted signal will make it to the receiver for the receiver to recover the clock and data consistently.

One of the key Cadence tools involved in this analysis is the Clarity 3D Solver. Without it, as in the title of this post, you will slow down your journey to success.

The Clarity 3D Solver can analyze complex connectors and the associated area of the PCB around the area where the connector is attached. This is known as the breakout region. In the past, the connector and the board would have been analyzed separately and the results "added" together. But that is not accurate enough for modern PAM4 high-speed signaling. The challenge in the past was to have the capacity to mesh the entire area accurately enough to do a full analysis. By "entire area" I mean PCB traces, pins, clips, and whatever other metal is in the connector. The Clarity 3D Solver scales to large numbers of servers in the cloud (or a data center) and so can handle the entire analysis without requiring either a ridiculous amount of runtime, or a ridiculous amount of memory.

Clarity Is #4

Every year, John Cooley collates a list of users' votes to list the products of the year. And just earlier this month, his regular email announced that Clarity is #4. Of course, Avis was famous for having a slogan for 50 years "We're #2, we try harder". Well, we're #4 so we try really, really hard. But actually, we are #1 (twice) as well in Cooley's list with Palladium and Protium's fast compile. And we are #2= with Spectre X, too.

Cadence announced Clarity 3D Solver in April last year. I wrote about it that day in my post Bringing Clarity to System Analysis. John surveyed his subscribers and discovered there was a lot of skepticism. He found that:

56% of users doubt Anirudh's secret "new" Clarity matrix solver

I'm not sure why "new" is in quotes like that, I promise that we didn't have the Clarity 3D Solver hidden away in the cellar for a decade to mature like fine wine.

But that skeptical attitude changed when people started to run benchmarks:

It's results, NOT algorithms, dummy!

Or, going into a bit more detail, one of his anonymous commenters says:

We can now put our entire design into Clarity for analysis vs. breaking it up. When we break it up, we have to make approximations and sacrifice some accuracy. Not with Clarity.

You can read the whole of John's post on his website. Of course, it is in John's inimitable cheesy^TM style (I wonder what he really thinks!). Anyway, I gave him a call to see if there was any more clarity about Clarity. He told me:

The thing that impressed me is that this is six hands-on user benchmarks. You have no idea how difficult those are to get. Engineers all want to share their data but don't want to get caught up in corporate politics. I have to give them the cloak of invisibility.

Video

Here is the video True 3DEM Analysis and Thermal Analysis Using Clarity and Celsius Solvers. This was made at embedded world in Nuremberg, Germany, which I think is the last trade show that Cadence attended. If you watch the video, you will get a bit more detail on doing electromagnetic analysis with Clarity (and thermal analysis with Celsius). You will also learn how to pronounce Srdjan Djordjevic who is the presenter.

Learn More

Here's the Clarity 3D Solver product page (with a button to download the whitepaper).

Cooley's page about Clarity being #4 (but as I said, we're #1 as well...see my post Protium and Palladium 1st= for more about that).

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