Programmable Switches for Programmable Logic Devices
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The document discusses different types of programmable switches used in programmable logic devices (PLDs) including fuse-based switches, antifuse switches, static RAM switches, EPROM switches, and flash memory switches. It provides details on the operation, advantages, and disadvantages of each switch type. It also compares the different switches based on manufacturing process, reprogrammability, size, resistance, capacitance, power consumption, volatility, and radiation immunity. The ideal properties for switches in PLDs are also outlined.
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Programmable Switches for Programmable Logic Devices
- 1. Programmable Switches Dr Usha Mehta usha.mehta@nirmauni.ac.in
- 2. Acknowledgement This presentation has been summarized from various books, papers, websites and presentations related to the topic all over the world. I couldn’t remember where these large pull of hints and work come from. However, I’d like to thank all professors and scientists who created such a good work on this emerging field. Without those efforts in this very emerging technology, these notes and slides can’t be finished. 2 Usha Mehta 08-12-2023
- 3. Programmable Switches Programmable switches are used in PLD for • Connections • Wire • Logic • Input-Output • Configurations • Logic Blocks 3 Usha Mehta 08-12-2023
- 4. Ideal Programmable Switch • An FPLD contains thousands of such programmable switches. • Hence the switches should • Occupy very less area • Have very low ON resistance and very high OFF resistance • Have very less parasitic capacitance • Easily fabricated in large number with high reliability 4 Usha Mehta 08-12-2023
- 5. • Programmable switches may be • Permanent • One time Programmable • Non Permanent • Reprogrammable 5 Usha Mehta 08-12-2023
- 6. Fuse • One Time Programmable (OTP) • Initially: SHORT, • After programming: OPEN 6 Usha Mehta 08-12-2023
- 7. Array Logic by Fuse 7 Usha Mehta 08-12-2023
- 9. Fuse Programmed Logic Array 9 Usha Mehta 08-12-2023
- 10. Antifuse Technology • Opposite to Fuse • Initially: OPEN • Programmed by forcing a current through it: SHORT • Actel calls it “Programmable Low-Impedance Circuit Element (PLICE)” 10 Usha Mehta 08-12-2023
- 11. Antifuse Structure • Two metal layers sandwich a layer of non-conductive, amorphous silicon. When voltage is applied to this middle layer, the amorphous silicon is turned into polysilicon, which is conductive. 11 Usha Mehta 08-12-2023
- 12. MOS Structure of Antifuse 12 Usha Mehta 08-12-2023
- 14. Antifuse: Advantages-Disadvantages • Advantages • Very small in size hence allows denser switch population • Low series resistance • Low parasitic capacitance • Disadvantages • One time programmable • Requires extra circuitry to deliver the high programming voltage • Requires a specific process ( not same as normal standard integrated circuit process) 14 Usha Mehta 08-12-2023
- 15. Static RAM Programmable Switch • Use SRAM Cell to control pass transistor or multiplexer by the bit-content in the SRAM cell. 15 Usha Mehta 08-12-2023
- 17. • Disadvantages • Volatile • External Permanent memory required • Large Area Required • Advantages • Easily and quickly reprogrammable • Requires only standard integrated circuit process technology for fabrication. No special requirements like Antifuse 17 Usha Mehta 08-12-2023
- 18. EPROM Technology • Use of Erasable Programmable Transistor as switch • It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages than those normally used in digital circuits. 18 Usha Mehta 08-12-2023
- 19. EPROM Structure • A FET with floating gate • The floating gate has no connections to other parts of the integrated circuit and is completely insulated by the surrounding layers of oxide • Storing data requires applying a higher voltage to the transistors. • This creates an avalanche discharge of electrons, which have enough energy to pass through the insulating oxide layer and accumulate on the gate electrode. • When the high voltage is removed, the electrons are trapped on the electrode. • Because of the high insulation value of the silicon oxide surrounding the gate, the stored charge cannot readily leak away and the data can be retained for decades. 19 Usha Mehta 08-12-2023
- 20. EPROM as switch • Become Open path when programmed because of the electrons trapped on floating gate raise the threshold voltage of n Channel EPROM above VDD • Erasable/Reprogra mmable by applying UV light 20 Usha Mehta 08-12-2023
- 21. NOR based Flash Memory 21 Usha Mehta 08-12-2023
- 22. Comparison of Switching Technologies SRAM Antifuse EPROM EEPROM Manufacturi ng Process Easy Hard Hard Hard Reprogramm able? Yes (in circuit) No Yes (Out of Circuit) Yes (in circuit) Size Large (12X) Small (1X) Small Small ON Resistance 600-800 Ohm 100-500 Ohm 1-4K 1-4K OFF capacitance (fF) 10-50 1-3 10-50 10-50 Power Consumptio n Very less less High High Volatile? Yes No No No 22 Usha Mehta 08-12-2023
- 24. Market Use of Programmable Switches • Actel: Antifuse • Xilinx: SRAM • Altera: EEPROM/FLASH 24 Usha Mehta 08-12-2023
- 25. Radiation Immunity of Programmable Switches Antifuse SRAM FLASH Configuration has been designated as hard regarding SEEs. Configuration has been designated as the most susceptible portion of circuitry. Configuration has been designated as hard (but NOT immune) regarding SEEs No need of mitigation Strong need of mitigation No need of mitigation 08-12-2023 Usha Mehta 25