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Multiple Drain Transistor-Based FPGA Architectures
Drew Carlson Pankaj Kalra EE241 Class Project May 9, 2005
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Multiple Drain Transistors
Goal: Reduce cost per fxn Multiplexing + memory in single cell Multiple Drain Transistor [1] Non-volatile switch connects/disconnects drains from channel Similar to: Sidewall Flash Memories [2, 3] Scalable Reverse-read Benefits: Forward write/read Larger effective widths n/n- n+ P+ Qnit Si3N4 SiO2 S D gate Drain1 S D2 Dn [1] A.Carlson and T.-J. King, Device Research Conf., 2005, to be published. [2] M. Fukuda et al., IEDM Technical Digest, pp , 2003. [3] Y.K. Lee et al., J. Vac. Sci. & Tech. B, 22, pp , 2004. Carlson / Kalra – MDT-based FPGAs
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Carlson / Kalra – MDT-based FPGAs
Building a SPICE Model Subcircuit Model Driving & coupling MOSFETs Effective widths from geometry calculations Resistive LDDs Process Model Square law approach 1-drain MOSFET I-V curves from MEDICI (device sim.) Fit SPICE parameters to curves S D1 D2 G Curves: SPICE Markers: MEDICI Vgs = 0.6V, 0.8V, 1.0V. Carlson / Kalra – MDT-based FPGAs
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Field Programmable Gate Arrays (FPGAs)
Routing Fabric Horizontal & vertical channels meet at switch blocks 70-90% die area Limiting Constraint: Area (# switches) x (switch area) Minimize either / both Logical Blocks Program to any function w/ Look Up Table (LUT) LUT D Q > 6T Switch Logic Block [1] H. Schmit and V. Chandra, “Layout Techniques for FPGA Switch Blocks,” IEEE Trans. VLSI Systems, vol. 13, pp , Jan Carlson / Kalra – MDT-based FPGAs
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Carlson / Kalra – MDT-based FPGAs
Smaller Switches Pass Transistor Up to 7x area reduction Comparable performance vs. Buffered Switch Savings in fanout (pass) SRAM (n drains) (multiplicity n) SRAM SRAM Carlson / Kalra – MDT-based FPGAs
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Carlson / Kalra – MDT-based FPGAs
Smaller Switch Blocks Disjoint Channel Width = 4, Flexibility = 3, Wpass=10Wmin 4.37μm x 5.81μm (vs. 124 μm2) 3 MDT / switch Carlson / Kalra – MDT-based FPGAs
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Carlson / Kalra – MDT-based FPGAs
More Routability Universal Channel Width = 4, Flexibility = 9, Wpass=10Wmin 17.73μm x 6.57μm (vs. 394 μm2) Carlson / Kalra – MDT-based FPGAs
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Carlson / Kalra – MDT-based FPGAs
SRAM LUT SRAM . Critical Path S0 S1 S2 S3 OUT . LUT OUT S0 S3 Total Area 185 Amin Delay of critical path = 415ps Amin (area of minimum width transistor) = 0.324μm (90nm process) Carlson / Kalra – MDT-based FPGAs
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Carlson / Kalra – MDT-based FPGAs
MDT MUX S0 Precharge Output S1 1 Pair of double-drain MDTs and pair of pass transistors 41 MUX 41 MUX Store configuration bits during programming Reading 0 Select MDT drain pulled to low Select Pass tx. Reading 1 Precharge signal pulls output to high Carlson / Kalra – MDT-based FPGAs
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Carlson / Kalra – MDT-based FPGAs
MDT LUT S0 Precharge S1 . S2 S3 OUT Total Area 87 Amin Delay of critical path = 370ps 53% area reduction Carlson / Kalra – MDT-based FPGAs
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Carlson / Kalra – MDT-based FPGAs
Programming of MDT Programming needs not be very fast (done offline) Store all the configuration bits in a shift register Tradeoffs Charge Pumps to get high voltage level MDT Programming Require high voltage pulse (VG=3V, VD=5V) Level-shifter circuit to generate high-voltage pulse Feedback pMOS type Cross-coupled pMOS type Level Shifter Out Vdd Vpp In Carlson / Kalra – MDT-based FPGAs
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Carlson / Kalra – MDT-based FPGAs
Summary Novel device structure studied for reconfigurable applications MDT based FPGA architecture is proposed Routing fabric : up to 80% area reduction LUT: up to 53% area reduction Carlson / Kalra – MDT-based FPGAs
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