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.