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Programmable logic devices

2017-12-23 14:26  
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In a market you can find a bunch of programmable logic devices – PLD. They can be small scale integrated – SSI, medium scale integrated- MSI, mask programmed gate array – MPGA (MPGD – masked programmable logic devices). Now the most popular are FPGA (Field Programmable Gate Arrays).

What is a difference between FPGA and MPGA? MPGA are hard-coded during manufacturing and cannot be erased or reprogrammed while FPGA are programmable – usually EEPROM or SDRAM.

Of course there are other differences between FPGA and MPGA. One of them is speed. MPGA usually is faster as MPGA needs fewer elements to form logic gate while FPGA needs additional elements to enable programmability – this adds additional resistances and capacitances in circuits. But today’s technology allows reaching significant speeds with FPGAs too.

Other difference may be integration. As we mentioned MPGA requires fewer elements to form one logical gate, they can contain more logical gates, but again the area of chip is also limited by pin number- this different becomes meaningless.

The main criteria of choosing MPGA or FPGA would be:

  • Speed;
  • Density;
  • Cost;
  • Manufacturing;
  • Prototyping;
  • Ability to modify;
  • Simulating.

    If we need to prototype a project you will chose FPGA as it allows reprogramming multiple times. When you release your design to mass production – wise choice is to use MPGA as it cost less because of mass programmability, speed and simpler technology.

    Two types of PGA are FPGAs and Complex Programmable Logic Devices – CPLDs. FPGA offer the highest amount of logic density, the most features, and the highest performance.

    FPGA RAM CELL

    The largest FPGA now shipping, part of the Xilinx Virtex line of devices, provides eight million “system gates” (the relative density of logic). These advanced devices also offer features such as built-in hardwired processors (such as the IBM Power PC), substantial amounts of memory, clock management systems, and support for many of the latest, very fast device-to-device signaling technologies. CPLDs, offer much smaller amounts of logic gates- up to about 10,000 gates.

    CPLD EEPROM CELL

    But CPLDs has predictable timing characteristics and are ideal for critical control applications. CPLDs require less of power and are inexpensive comparing to FPGA, making them ideal for cost-sensitive, battery-operated, portable applications such as mobile phones and digital handheld assistants. CPLD programmable logic devices usually are EPROM or EEPROM based.


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