TUNABLE THRESHOLD LOGIC GATE-SWITCHING SPEED AND ENERGY

 The below figure is the circuit diagram of an MQW-HBT 3 input threshold gate




Figure 1 MQW-HBT 3 input threshold gate

  • To operate the gate,the light should be above the excitonic peak
  • The Load resistor current is the superposition of currents in the MQW-HBT
  • P-i-(MQW)-n diodes in parallel with HBTs modulate light of the same wavelength

In the figure,a load resistance is used with a variable voltage supply. A Zener diode is connected in parallel with the MQW-HBT. It prevents damage due to accidental high voltages. For the light source,a tunable laser is used.

  • When there is no light on the MQW-HBT, there is no current and no voltage drop across the load
  • The function of the gate can be altered by changing the supply voltage

For a  NOR function,

12v power supply and when none of the inputs is 1(illuminated),the output is 1 and if any of the input is 0,the output is 0

For a Inverse Carry Gate,

18v power supply  and when two or more inputs are 1,the output is 0,else output is 1

For a Nand Gate,

27v power supply and when all inputs are 1,output is 0,else 1



                                                                Figure 2:Truth table
 
SWITCHING SPEED AND ENERGY

  • Optical systems can have massive Parallelism and better connectivity
  • Optical Interconnects can be programmable.They can respond to basic commands with a generalized cross bar switch
  • In a kind of Optical Architecture,all possible optical inputs can be connected to optical outputs through a 2 Dimensional switch array
  • The switch element in the array can be an opto electronic switch or SEED
  • A light source can illuminate a entire column of the 2D array
  • Based on the input information,The switch can be programmed in real time
  • The important parameters of a switch are Switching Speed and switching Energy
  • Dividing switch energy by switch time/speed gives the switching power
  • The switching energy of a bipolar controller modulator circuit is estimated to be 100fJ
  • By increasing electrical energy and with better device design,optical switching energy can be reduced.














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