Low power 32-bit bus with inversion encoding Wei Jiang ELEC 6270

Power Consumption by Bus High capacitance lines High capacitance lines High switching activities High switching activities Reduce power dissipation by reducing the number of transitions Reduce power dissipation by reducing the number of transitions

Bus Invert Encoding TransmitterReceiver 32 TransmitterReceiver 32 ENCODERDECODER INV Conventional Bus Bus with Inversion Encoding

Bus Invert Encoding To minimize transitions in bus with large capacitance To minimize transitions in bus with large capacitance Additional Line: INV Additional Line: INV Encoding: Encoding: Di, if INV=0 Di, if INV=0 Di XOR 1, if INV=1 Di XOR 1, if INV=1 Decoding: Decoding: Di XOR INV Di XOR INV M. R. Stan Proposed by M. R. Stan

Design of Encoder

Majority voter Majority voter circuit decides according to Hamming distance whether to invert or not the next value Digital voter: accurate Analog voter: simple Stan, TVLSI 1995

Counter & Comparator

Falling Edge Detector/Indicator

Design of Decoder

Simulation – Best Scenario

Simulation – Worst Scenario

Signal Transitions Total Power Dissipation Power Dissipation of Transmitter Power Dissipation of Receiver Signals forms

Simulation – Average

Conclusion Average power by transmitter/receiver (C L =0) Average power by transmitter/receiver (C L =0) For conventional bus: mW For conventional bus: mW For inverted bus: mW For inverted bus: mW Encoder/Decoder overhead: mW Encoder/Decoder overhead: mW Increase the power dissipation of low capacitance bus Increase the power dissipation of low capacitance bus Reduce dynamical power dissipation by roughly 10% if bus load capacitance per bit is 1pf; 25% for 2pf of load capacitance; and more for even higher capacitance Reduce dynamical power dissipation by roughly 10% if bus load capacitance per bit is 1pf; 25% for 2pf of load capacitance; and more for even higher capacitance The actual power reduction depends on both the bus load capacitance and the number of transitions: The actual power reduction depends on both the bus load capacitance and the number of transitions: More than 17/close to 32: bus inversion may reducing power More than 17/close to 32: bus inversion may reducing power Less than 17: bus inversion may increase power Less than 17: bus inversion may increase power

Thank You Simulation Simulation TSMC 0.35um Process TSMC 0.35um Process Synopsys HSPICE Synopsys HSPICE References References M. R. Stan and W. P. Burleson, Bus-invert coding for low- power I/O, IEEE Trans. On VLSI Systems, Vol.3, No.1, pp.49-58, 1995 M. R. Stan and W. P. Burleson, Bus-invert coding for low- power I/O, IEEE Trans. On VLSI Systems, Vol.3, No.1, pp.49-58, 1995 T. Lindkvist et al, Deep Sub-Micron Bus Invert Coding, NORSIG 2004, p , June 2004 T. Lindkvist et al, Deep Sub-Micron Bus Invert Coding, NORSIG 2004, p , June 2004