Multichip approach extends range of DSP and A/D combo

Analog Devices has used multichip packaging to provide a new version of its Blackfin digital signal processor (DSP) with a 12bit A/D converter and up to 4MB of flash.

“It’s a true 12bit converter,” claimed Anders Fredericksen (pictured), marketing segment manager for motor control. “It has an effective number of bits [ENOB] of 11.7. The nearest to this that we found for an integrated A/D converter was 10.”

“With 4MB, it is not the biggest amount of flash memory in the world but in the domain below $10 it is,” Fredericksen added, noting that the use of separate dice – the flash is stacked on top of the DSP while the A/D converter sits alongside to improve noise isolation – is potentially more costly. “But we can optimise each of the processes independently.

Pointing to a decapped version of the package, Fredericksen said: “There is more space in here. There might be future designs that embed other things. It is a proven technology now. And it gets flexibility into the hands of our customers.

The processor runs at up to 400MHz and is built on a 90nm process while the flash uses a 65nm technology for density. The A/D converter uses an older 0.25µm that is more amenable to analogue design.

“System-in-package is something that we have been working with for quite a while now. We believe we know the cost, performance and other constraints well,” said Fredericksen.

With the BF50x series of DSPs, Fredericksen said Analog Devices is aiming primarily at advanced motor control and new applications in renewable energy where more efficient algorithms for charging are needed.

“For the past four or five years, most of the heavier algorithms have been forced into ASICs and gate arrays because they need really high performance DSP. This can do both control and signal processing,” Fredericksen claimed.

He said the decision to include 4MB flash was driven by application trends. “There are applications in motor control we are looking at now that are in the 1 to 1.5MB area. By picking 4MB we have headroom for other parameters. We have selected a size that lets the mathematicians and architects to think clever.

“A lot of the mathematical models used for control have been dumbed down because there wasn’t sufficient performance to run the full implementations. The most recent work has been done on powerful machines,” said Fredericksen.

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