Q. My SPICE simulation worked perfectly, but now I've a large production
batch which doesn't meet its specification.

A. Analog circuit simulation is one of the most valuable tools that has
emerged over the last two decades, and my company offers an impressive array
of SPICE models to aid circuit designers. But simulation is not real life.
SPICE models rarely emulate all the second- and thirdorder effects which
make analog circuit design so challenging. It is critically important to
build, and exhaustively test, hardware versions of your analog designs, not
just run interminable simulations.

At high frequency, and with very high precision designs, it is even
important to make the prototype as similar to the final production layout as
is possible, because parasitic inductance and capacitance from the
printed circuit
board can have a substantial effect on HF performance and cause big
differences between the simulation, the breadboard and the final production
version.

Designs in their hundreds at Analog hang in the air,
Ideas from the Valley, ideas from the timid or bold,
Designs that are pearls and designs that are rubbish are there,
And there with the rest are designs that will never be old.

There's circuits from everywhere that triple Es may reside,
And many to count are the abstract and many of use,
And many that seem so attractive they can't be denied,
But few that perform when you build 'em and turn on the juice.

I wish one could know them, I wish there were tokens to tell
Those fortunate circuits that work when you turn on the power;
And then one could publish them freely and not strike a knell
For our firm's reputation for circuit ideas that inspire.

But now you may stare as you like but you cannot devise
Infallible ways to ensure that success be foretold;
They send to the ceiling the smoke of untimely demise
Designs that will die on their breadboards and never be old.

(With apologies to A. E. Houseman)
This is a parody of one of the poems (XXIII) in Houseman's "A Shropshire
Lad."

From: EDN (06-01-19), Rarely Asked Questions - Strange but true stories from
the call logs of Analog Devices
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