Flash FPGAs And Mixed-Signal Design

Jan. 12, 2006

Where do I need analog and flash memory in a digital system? Many systems accomplish most of their tasks using digital logic. But the logic chips themselves?FPGAs, ASICs, ASSPs, etc.?all require some analog support. That support takes the form of power-

Dave Bursky

Where do I need analog and flash memory in a digital system?

Many systems accomplish most of their tasks using digital logic. But the logic chips themselves?FPGAs, ASICs, ASSPs, etc.?all require some analog support. That support takes the form of power-sequencing control, voltage sensing to detect brownout conditions, power management, and temperature sensing to provide dynamic control of fan speed, clock speed, and even operating voltage.

For example, power sequencing requires a combination of logic and analog sensing. The logic controls the order in which the various powersupply voltages are applied to the chips, and the analog senses the voltage levels. To implement the sequencing function, many RAM-based FPGA users and ASIC/ASSP users have added a small flash-based programmable logic device and a comparator to do the job.

If a flash-based FPGA or anti-fusebased FPGA is used in the system today, the ?instant-on? aspect of those FPGAs allows the sequencing function to be incorporated into the FPGA. RAM-based FPGAs and other circuits that load data into RAM upon power-up would still require external sequencing logic to ensure they start up in the proper state.

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About the Author

Dave Bursky | Technologist

Dave Bursky, the founder of New Ideas in Communications, a publication website featuring the blog column Chipnastics – the Art and Science of Chip Design. He is also president of PRN Engineering, a technical writing and market consulting company. Prior to these organizations, he spent about a dozen years as a contributing editor to Chip Design magazine. Concurrent with Chip Design, he was also the technical editorial manager at Maxim Integrated Products, and prior to Maxim, Dave spent over 35 years working as an engineer for the U.S. Army Electronics Command and an editor with Electronic Design Magazine.