Analog design is NOT black magic… but it is VERY hard
Posted by mike demler on October 4th, 2007
Analog design is Black Magic??? Recently there have been two occurrences where this description of analog design has been used; a panel discussion at the IEEE SOC Conference in Taiwan (09/27/07), and Mike Santarini’s blog (09/18/07) at EDN Magazine.
From the Cambridge Dictionary online:
black magic noun
a type of magic that is believed to use evil spirits (= beings which cannot be seen) to do harmful things
That’s a pretty derogatory description of analog design, in my opinion. Where does this misguided notion come from? Is analog design so hard that non-designers think it must be black magic?
Here’s my definition of analog design:
analog design noun
- An art practiced by skilled engineers who possess the creativity and expertise to construct high performance circuits from individual transistors and passive components.
- May appear to be magic compared to digital design
Yes… transistors and circuits, not gates and RTL. Take the simple case of a 2-transistor inverter. To a digital designer it’s quite simple; B = not A (or A’).
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The Digital View |
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Now let’s take an analog view of the same two transistors. To an analog designer, we can make those two transistors into an amplifier: vb = gmvaro, gm = Cg·W/L· (va-vt0)
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The Analog View |
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In the digital case the designer is an expert in logic or writing RTL, and the circuit details are accounted for by a synthesizer. In the analog case the designer is a circuit expert, and the (increasingly complex and variable) device model details are accounted for in a simulator.
That doesn’t make either analog or digital design black magic! But both cases provide excellent examples of how advances in EDA tools have contributed to increased designer productivity and IC innovation. I have to address one of the EDN blog commenters who claimed “it will be a very unusual moment when someone actually comes up with an analog EDA tool that helps an analog designer”. Wow, and I thought the “black magic” myth was bad!
Unusual to make an analog EDA tool that helps a designer? Not hardly! The problem is that the first introduction of the analog designer’s primary EDA tool came before any of these folks were paying attention, in fact before there even was an EDA industry… and it was SPICE! Ten years from now, when logic synthesis has established as long a history as circuit simulation, I wouldn’t be surprised to hear the same type of comments about digital EDA.
SPICE created just as big a paradigm shift as Design Compiler did, it just came about 10-15 years earlier. If you look back at how IC design was done before SPICE simulation became so pervasive, you would see that breadboard prototyping with discrete transistors, paper & pencil, maybe even a slide rule calculation, were the only tools available. Can anyone imagine designing a 5GHz RF SoC in CMOS without modern analog EDA tools, starting with simulation? And that’s just one example of leading edge analog design from the most recent ISSCC.
The EDA industry certainly has not stood still on progress in analog tools. I could go on and on about layout tools, optimizers, waveform analyzers and many more, but let’s just look at analog circuit simulation. There have been more than thirty years of major innovations in circuit simulation that have powered the advances in analog design that some apparently seem to find so mysterious.
Here is a list of just a few of the significant advances in circuit simulation over the last 35 years:
- 1971: SPICE 1.0
- 1978: SPICE-2g6
- 1981: HSPICE – the 1st successful commercial SPICE. The Level-28 model
- 1989: SPICE-3
- 1995: 1st generation Fast-SPICE, SPICE-HDL co-simulation
- 1996: BSIM-3 model
- 1996: Introduction of Verilog-A behavioral modeling
- 2000: 2nd generation hierarchical Fast-SPICE, Verilog-AMS
- 2007: Multi-threading and parallel SPICE, new special-purpose Fast-SPICE engines
Analog design. An art. A science. A rare skill. But black magic it’s not!
I welcome your comments.
-Mike
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Mike,
Enjoyed the article.
So why is analog design like black magic?
It often requires a long apprenticeship to be proficient in the dark art of analog design. The connection between cause and effect is tenuous at best with so many physical and electrical interactions between components. A bad ground and some stray capacitance can make designs seem to be haunted by ghosts or troubled by gremlins.
And analog designers are a small minority. The design team usually has one analog engineer off in a corner somewhere who remembers how to bias a vacuum tube and has his ‘familiars’ that only he knows how to use to fix problems. He might use SPICE but never relies on it.
More could be said, but then I might be accused of necromancy myself.
+G
Enjoyed your article Mike.
When I mention analog in discussions today I get comments like “old school”.
My response is Digital is easy if you understand analog.
Young designers often say that High speed gigabits per second is as complex as gigahertz amplifiers and I disagree.
The threshold range of high speed is hundreds of millivolts digital. Analog RF circuits do not have that luxury. The PCB layout also weights to a greater part of the analog equations than its digital counterpart.
I liked the article.
Ya, it may not be a black-magic, but it is hard.
It needs a totally different apporach to solve problems then what digital would need.
Digital might get complex in terms of # of Tx used, but analog can be very complex with even a single Tx.
Overall, very good article and good view. thanks!
rajesh gupta
Well,
I wish these Simulator folks stay away frm Analog Design.A lot of such tool is making this Art lose its Arts.Lke many of the neo I see take the topolgy run all corners simulation and close the project..
God..before one makes any simulation better to go to an experienced guy who need not run simulation and tell where it is going to fail..?Some times they catch if something has been screwed up in the transistor model itself…Hope this class of Engineering prevails..
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