5. Application Examples

1. 5. Application Examples 5.1. Programmable compensation for analog circuits (Optimal tuning) 5.2. Programmable delays in high-speed digital circuits (Clock skew compensation) 5.3. Automated discovery – Invention by Genetic Programming (Creative Design) 5.4. EDA, analog circuit design 5.5. Adaptation to extreme temperature electronics (Survivability by EHW) 5.6. Fault-tolerance and fault-recovery 5.7. Evolvable antennas (In-field adaptation to changing environment) 5.8. Adaptive filters (Function change as result of mission change) 5.9 Evolution of controllers 1

2. Automated synthesis of digital circuits Evolution at High Specification Level hardware Description Language (using e.g. VHDL) module.0 ls_comp.1 ls_pin.1 ls_action.2 COMPILE SIMULATE ls_comp.0 comp.3 cond_action.1 SYNTHESIS Evolution at Low Specification Level Gate Diagram of FPGA (using Configuration Bits) Chromosome Representation SIMULATE DOWNLOAD Implementation Level Programmable Logic Device Circuit Specification: - At Block level, using a hardware description language, such as VHDL, is used as the genetic encoding of the circuit. The automated synthesis optimizes the HDL code, compiles and downloads into a Programmable Logic Device. - At the logic gate level, the configuration bits in the programmable device are used as the genetic encoding of the circuit. The automated synthesis optimizes the configuration bits and download into a Programmable Logic Device. Circuit Evaluation: The evaluation of the digital design is done by simulation or by downloading the configuration bits of the candidate design into a Programmable Logic Device. The design performance is evaluated by using the input-output mapping for a combinatorial circuit and by tracing the states sequence or the state transition paths for a sequential circuit.. Achievements: Early Successful automated synthesis of digital circuits, such as 6-in MUX (25 gates) [KIT96], a 4-bit comparator (23 gates) [HIG96], and a sequential adder (50 gates) [ZEB96]. - Automated synthesis of an HDL-program representing a circuit wih 8 control states (using 100 gates) [HEM96]. More recently: Cartesian Genetic Programming Automated synthesis of HDL code (r0.0) module -> K_MOD name list_comp list_pin list_action (r1.0) name -> K_NAME (r2.0) list_comp -> comp (r20.3) comp -> K_INSTRIN inst_name HDL code for ant control Automated synthesis of Logic Gates A0 001110010001111010101010000 A1 OUTPUT 1: A>=B 0: A< B Chromosome Representation B0 B1 2-channel 2-bit comparator 2

3. Evolution of digital gates at transistor level • New digital cells, for specific applications, e.g. extreme temperatures, radiation, very low voltage, new component devices (e.g. 4-gate transistor), etc. • Analog characteristics of sub-micron, high-speed 3

4. Coverage of functional space • Check design corners, not only typical values. Many tests for same circuit. Vdd, temperature are most common, some are application specific. • Need for comprehensive testing to ensure that evolved solutions cover the intended operational space; • Contrary to conventional design, no assumptions on the circuits’ performance outside the points tested during evolution can be reliably made. 4

5. Combinations of input logic levels • Candidate logic circuits should be tested in transient analysisfor all possible transitions of combinations of input levels; • For example, a circuit may respond well as an AND gate to input combinations of levels 0-0, 0-1, 1-0, 1-1. However, it may have a long switching time when inputs 1-1 following 0-0 - and not 1-0 as above, which is not tested in the simple scheme; • Increased transient analysis: seven input configuration cases opposed to four. 5

6. Fan-out • Loading problem: preliminary experiments showed that evolved circuits were not able to drive similar circuits; • Problem: Input/Output impedance of circuit to be evolved is not known in advance; • Use of domain knowledge may help: in the case of logic gates we constrain the circuit inputs to connect only to transistor gate terminals, opposed to source or drain: increase input resistive impedance. 6

7. Time constants • Timescale Problem: preliminary evolved logic gates changed their behavior over a "frequency range“, i.e. different responses when tested with slow/DC signals and faster input changing signals; • Testing in micro-seconds timescale → Transient solutions; • Testing in seconds timescale → Slow gates; • Solution: extend the transient analysis duration to avoid transient solutions while keeping the transient analysis step small enough to assess the gate speed. 7

8. Testing to design corners Testing Design Corners through Mixtrinsic Evolution: • Robustness to changes in model accuracy, temperature and power supply (Vdd); • Have only the final evolved circuits tested to all design corners ( 10% variations of Vdd, temperatures from –20oC to 200oC, slow/fast transistor models) or • Accelerate evolution via mixtrinsic evolution, biasing small fraction of the population to be tested for corners. 8

9. Silicon validation results • Several circuits evolved at transistor level and then fabricated on a prototype ASIC on a HP 0.5 micron process; • Circuit representation: the chromosome encodes the circuit topology (MOS transistor connections) and the transistors’ sizes (width and length); • Number of components was imposed, or limited to maximum 8; • Most experiments used populations of 40 individuals and a number of 400 generations. 9

10. Silicon validation results In1 In2 Out NAND response Evolved circuit NOR response 10

11. Operability in Cascaded Designs Error Detection Adder fabricated in silicon Silicon results 11

12. Switching Speed Tests • Gates were evolved to work at only 1kHz but could actually be switched at higher frequencies; • Testing maximum speed of NAND gate for 1pF load: in simulation the NAND functionality does not work for a switching period of 2s, while in silicon the switching time can be decreased to less than 1s. 12

13. Switching Speed Tests Simulation Silicon NAND gate: Load 1pF, 2us switching time The inputs were applied in the following sequence: 00→11→01→11→10→11→00, to test all possible transitions 13