Published March 2000

ANALOG PLD ANYONE?

by Tom Cantrell

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The 1s and 0s are coming! The 1s and 0s are coming!

Humans are analog. From day one we’ve relied on continuous inputs, namely the five senses, to make our way through life. But, in the last 50 years, the dynamic 1s-and-0s duo of the digital age started throwing their binary weight around.

In the beginning, only the high and mighty were able to get up close and personal with 1s and 0s. These days, at least in the industrialized world, it’s rare to find anyone who isn’t dealt a daily dose of digital. Speaking for myself, there’s hardly a moment in the day when I’m more than a few feet from some digital doodad.

Even our pets are going digital, evident in electronic ID tags and smart kitty boxes. Will there come a day when Whiskers would rather click a mouse than chase one?

BREAK THE CHAIN

Though the analog gap is closing, it won’t disappear. Ultimately, the 1s and 0s must be converted to and from analog if humans are to make sense of it all. Doing that relies on what’s known as the signal chain.

Consider what’s involved in converting some continuous real-world phenomenon (heat, light, pressure, etc.) into bits in memory. As shown in Figure 1, the chain is comprised of links that perform specific roles.

Figure 1—1s and 0s need not apply. Traditionally, the links in the signal chain between sensor and A/D converter (i.e., the Analog Front End or AFE) have been the realm of purely non-digital chips, such as amplifiers and filters.

The first link in the chain is the sensor itself, which is responsible for translating the real-world phenomenon into an electrical surrogate. Unfortunately, the signal is often tiny and prone to pick up noise, so links are usually required to filter and amplify the raw output of the sensor. The signal is now suitably attired for presentation to the A/D link that translates the continuous phenomenon to the discrete-time digital domain, home turf for computers.

Once digital, the signal can be further processed. Indeed, the neat thing about digital signal processing (DSP) is the opportunity it offers to reduce cost and improve performance compared to circuits on the analog side of the A/D. Nevertheless, DSP can only complement, not replace, the analog links in the chain. And, don’t be fooled by talk of digital sensors—the only true digital sensor is an on/off switch.

The recently announced Analog PLDs from Lattice Semiconductor push 1s and 0s across the A/D and into the realm of analog signal processing. It’s time to add a new chapter to the dog-eared op-amp cookbooks of yore. [1]

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