In analog, EDA tools cannot replace common sense

In analog, EDA tools cannot replace common sense

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By Peter Clarke

I know there have been many advances in software development for use in design projects. The digital design landscape has permanently been altered by the use of sophisticated software tools for use in design. Design tasks that used to take months can now be completed in days. Although these tools can still provide erroneous results if the setups are incorrect or the models and assumptions are flawed, the errors have vastly been reduced to the point of becoming an exception and not the norm.

The use of place and route software tools have also made completing large digital layouts as easy as running scripts for place and route with interactions for static timing analysis for meeting critical setup and hold requirements for digital blocks.

Is this the same for analog design? Are there equivalent tools for designing and completing layouts for analog blocks? Over the years I have seen tools, optimizers, called in to do the work of skilled analog design engineers. Many of the tools have made significant progress in helping designers make faster and timelier decisions. However, I do not believe that the time of replacing the analog engineer is here and won’t be for some time.

The current state of the tools means the tools cannot replace an engineer’s raw intuition for designing complex analog blocks. However, I do believe that optimizers do have their place for low-level simple analog design blocks that have loose or less stringent specifications.

When it comes to complex analog design, “you need to be able to walk with the electrons,” as a senior colleague said to me one time, to solve design problems and layout constraints.

Often times the appropriate solution requires different topologies or innovation. This cannot be handled by an optimizer that will optimize based on a given set of parameters and a given circuit topology. The optimal solution to the problem may need an innovative combination of known topologies or as I said the invention of new circuits.

These types of tradeoff must be made by seasoned engineers that can come up with new ways to solve these difficult problems. Sometimes simple common sense recognition of whether or not a particular topology is appropriate is needed.

I guess one may argue that with enough power and area a tool could make an existing topology work. I do not believe the outcome from such a design proposal is an acceptable solution as real estate and power on the new technologies is expensive. Ultimately this procedure that produces such sub optimal results will meet resistance from senior leaders once they understand the costs that such a brute force approach using a substandard topology will result in for the final design and layout.

So, I believe the seasoned analog design engineer is safe for the time being, but there are innovative software engineers trying to crack the problems associated with inferior and less sophisticated solvers for analog design and layout.

Furthermore, many companies are working tirelessly to improve the state of the art for these types of solvers and have made significant headway in this respect. Therefore, the best advice I can offer is to be diligent, stay creative, read alternate solutions of how similar analog design challenges were solved, and ensure that you have the bandwidth to stay relevant by creating appealing solutions that are low in power and area and meet the needs of the product.

Analog design engineers always want to realize analog designs with lots of margin which is appropriate in certain cases. However, be careful about adding too much margin that can cost significant power and area – risk tolerance should be part of your thinking. Ultimately, a seasoned analog designer should clearly understand the risk/reward tradeoffs with the solutions to the analog circuits they are creating and design appropriate circuits that meet the needs of the product without significant overhead.

How have cad tools changed your design strategy?

Do you believe they are practical for analog design?

Brandt Braswell is a distinguished member of the technical staff at NXP Semiconductors and focuses on the development of data converters, with an emphasis on delta-sigma conversion.

This article first appeared on EE Times’ Planet Analog website.

Related links and articles:

Analog synthesis remains remote

Taking analog circuits to lower voltages

Analog design and the age of digital correction

Time for custom, analog design tools to automate?

Layout-dependent effects in analog design

Constraint-driven analog place and route

Circuit matching and analog layout

Power routing in analog design

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