Automated synthesis of 8-Output Voltage Distributor using Incremental Evolution Yerbol Sapargaliyev, Tatana G. Kalganova School of Engineering and Design, Brunel University Uxbridge, Middlesex, UB8 3PH, UK {Yerbol.Sapar, Tatiana.Kalganova}@brunel.ac.uk Abstract The automated synthesis of the analog electronic circuit, including both the topology and the numerical values for each of the circuit’s component, is recognized as a difficult problem. This problem is aggregating considerably when the size of a circuit and the number of its input/output pins increases. In this paper for the first time the method of automated synthesis of the analog electronic circuit by mean of evolution is applied to the synthesis of multi-output circuit, namely 8-output voltage distributor, that distributes the incoming voltage signal among the outputs in filter-like mode. Using the substructure reuse, dynamic fitness function and incremental evolution techniques the largest analogue circuit has been evolved in the area that has 138 components. 1. Introduction The Evolutionary Electronics is one of the most promising areas of today’s electronics. It is also known as automatic design of electronic circuits with help of Evolutionary Algorithm (EA). EA together with a circuit simulation tool (or the real hardware) automatically designs the circuit for the given problem. The circuits evolved may have unconventional designs. The EA is nowadays mostly represented by Genetic Algorithm, Genetic Programming, or Evolutionary Strategy (ES). The general idea is the EA navigated by fitness values, provides randomly created and mutated chromosomes. Each chromosome encodes the structure for a circuit in the form of a genotype and has to be evaluated by a fitness function. The fitness function assigns each chromosome with a fitness value that defines how close the current hardware is to the target by its functional characteristics. Selecting the best chromosomes by their fitness, cloning them (and/or crossing them over), mutating and evaluating them compose the full cycle of the search process. According to the Darwinian laws of natural selection, running the cycle repeatedly will lead to the best individual. The successful circuits most of all depend on the evolutionary technique that one has worked out and applied. The evolutionary technique is a set of rules according to which, parameters of EA (e.g., mutation rate, crossover, selection), genotype length varying strategies [3], mutation types and the circuit representation techniques are designed and managed. Despite that recently the EA was successfully applied to the design of the range of analog circuits (low-pass filters [1], [2],[4],[6],[8],[9],[13]-[17],[20]-[22],[24],[25], high-pass filters[1],[14],[17],[20],[22], amplifiers [1],[4],[7],[11],[13],[18][19],[19],[20],[24],[26],[27], digital-to-analog and analog-to-digital converters [1],[5], computational circuits [1], [3],[23], other kind of circuits [1],[8],[11]), all the previously reported designs were the analog circuits with maximum two outputs [1]. By contrast with the evolutionary design of digital circuits, where the scalability problem caused by numerous inputs and outputs is tackled ([29],[30],[31]), in the analog domain we could not find any similar example. One reason is that the analog circuit with multiple outputs is supposed to perform a complicated signal processing providing the package of high-ordered output signals (in time) to the circuit’s outputs. The size of such kind of circuit may count hundreds of components that expand the solution space to search in drastically (about to b2k3l+ck+l, where k and l are the numbers of 2-pin and 3-pin components in the circuit and b, c are some constants). In this paper we described the successful attempt to overcome this issue by applying ES to the design of 8output Voltage Distributor. The conventional method of a circuit design could easily solve this task by utilizing the up-to-date digital signal processing circuits, such as controllers with built-in analog-digital-analogue conversion. However, purely analogue circuits, in comparison with digital ones, can provide considerably shorter delay in the circuit response and suggest the economy in components. The last argument becomes more vital if the difference in components between the competing circuits reaches hundreds of times. The next section overviews the previous work in the area. Section 3 introduces the whole evolutionary technique. Section 4 describes the experiment. And, finally, the last section concludes the paper. 2. Previous work The importance of analogue evolutionary circuit design is well described in [3] and [6]. In Table 1 we included the majority of the works in evolutionary analogue circuit design. Most of the works start from evolving a passive low-pass filter which consist of R,C,L components. A low-pass filter is a convenient tool for the probation of evolutionary technique and tuning the EA parameters towards the more sophisticated designs [9]. The second stage of probation of the technique is usually undertaken over the circuits that have already been evolved previously by other researchers, however these are much more sophisticated and consisted of R,C,L and Q (npn/pnp) components. Obtained by authors the computational circuits [10] encouraged to approach more complex circuits targeting the analog circuits that never have been designed before due to their complexity. The evolutionary design of complex circuits are numerously instantiated in digital domain, where according to [30] “designers have introduced various approaches, which can be divided into three classes: functional level evolution, incremental evolution and development”. Among these methods only “divide-and-conquer” ([1],[12]) were distinctly utilized in analog domain, however, as it can be seen from Table 1, the targeted circuits there were not complex enough to fully exploit the potential of the proposed techniques. The experiment described in this paper utilized the incremental evolution, last one we see as a case of more general “divide-and-conquer” approach. Incremental evolution has widely been exploited in digital circuit synthesis (i.e. [28], [30]). The essence of incremental evolution lies in decomposing the target into subtargets that are supposed to be evolved more easily than initial target. In our case, the 8-output Voltage Distributor was decomposed into 8 separate subcircuits each of which was connected to the same one source and had its own output (Figure 1). The evolution started from the first device and upon the completion of the task moved to the next one, and continued until it finally designed the 8-th subcircuit. The experiment is accepted as finished if all 8 subcircuits evolved with satisfied fitness. Since the experiment ran non-stop throughout all eight substages, the dynamic fitness function was introduced similar to “adaptive fitness schedule” from [7] that is, the fitness function was incremented “whenever the current fitness threshold was reached by at least one chromosome in a population”. Table 1. Notable advances on the evolution of analog circuits. SA is Simulated Annealing, CS is Clonal Selection, D&C is Divide-and-Conquer, Dev is Development Method Maximum inputs/outputs of evolved circuits Maximum circuit size evolved No No 1/1 22 Yes D&C 3/3 64 No No No No No No No No No Dev No Dev No No No 1/1 1/1 2/2 1/1 2/1 1/1 1/1 1/1 1/1 1/1 1/1 2/1 1/1 1/1 1/1 23 12 19 10 18 22 41 66 33 19 17 46 11 7 15 Year Type of EA Parameter optimization Substructure reuse Kruiscamp et al [27] 1995 GA No Koza et al [1] 1997 GP No Lohn et al [6] Goh et al [13] Zebulum et al [4] Grimbleby [15] Dastidar, et al [18] Ando et al [14] Sripramong et al [19] Shibata et al [23] Alpaydın et al [26] Fan et al [16] Chang et al Su [21] Mattiussi et al [8] Xia et al [24] Gan et al [20] Das et al [22] 2000 2000 1998 1999 2005 2003 2002 2002 2003 2002 2006 2007 2007 2007 2007 GA GA GP,GA GA GA GP,GA ES+SA GA ES+SA GP GP GA GA CS GA No No No GA GA GP,GA hill-climbing GA No No No No No No GA No No No No Yes No No No No Yes Yes Yes No No No Wang et al [12] 2008 GP GA No D&C 1/1 13 Kim et al [25] 2009 ES GA No No 1/1 14 Sapargaliyev et al [9] 2006 ES No No No 1/1 27 Sapargaliyev et al [10] 2009 ES No Yes 1/1 44 In this paper 2009 ES No Yes No Increme ntal 1/8 138 3. Evolutionary technique 3.3 Program structure and mutation types 3.1. Representation and embryo circuit We suggest five types of components that the targeted circuit would consist of: NPN bipolar transistor (Qn), PNP bipolar transistor (Qp), resistor (R), inductor (L) and capacitor (C). The linear (direct) circuit representation is proposed for use, similar to one that exploited in [4], where is every component of a circuit is represented as a particular gene, and each gene consists of exactly 4 loci corresponding to component’s features: component’s name, component’s nodes and component’s parameter (except Q). In such a way the whole circuit is represented by the column of genes that called “chromosome” of that particular circuit. The chromosome looks exactly the same as the PSPICE netlist, so, there is no necessity to convert the genotype into the netlist. Figure 1. Embryo circuit Figure 2. The N-output Voltage Distributor The embryo circuit is a group of components (including a source of input signal) that is predetermined for the particular circuit. Mostly, these components are located at the circuit’s inputs and outputs. On Figure 1 there is the embryo for 8-out Voltage Distributor. It consists of source of input signals (V_IN), eight source resistors (Rs) and eight load resistors (Rl1…Rl8). The embryo also have two sources of direct voltage suggesting the evolution to choose between (or use both) 15V and 1.5V. Figure 3 generally shows the algorithm of the experiment. It consists of 4 main blocks that have been coded and united in one C++ program. Figure 3. The flowchart of the experiment The Start-block provides the population of embryo chromosomes in the form of PSPICE netlists to the ES block. At this stage the embryo is cloned to amount of the population number, and then every clone is grown up randomly with the help of 5 starting components described in section 3.1. The ES block contains and applies the particular parameters of ES, such as: mutation rate, population size, selection criteria (fitness function) and termination terms. First of all, the ES block gets the whole population of size P with the fitness value assigned to each chromosome from the previous block. According to the prescribed selection value S% (usually from 1 chromosome to 50% of the total population), it chooses the best S% of the chromosomes as parents for the next generation. Then, the ES block clones each of the selected parent chromosome in amount of (P*S/100) per individual that makes the population complete again. After that, the block applies the mutation procedure to each individual. There are totally 4 types of mutations, which are the Add_new_component_mutation (ANEM), the Delete_component_mutation (DEM), the Circuit_structure_mutation (CSM), last one includes 3 subtypes: component_name_mutation, component_pin_ mutation and component_parameter_mutation. We also regarded the Substructure_reuse_mutation (SRM), during which the group of genes are modified at one procedure, as another type of mutation, since it is just another way of chromosome modification. Each mutation modifies M% of the total amount of the chromosome’s loci, where M is the prescribed mutation rate value (usually varying from 0 to 10%). Since any gene (whole component) contents exactly of 4 loci, the ANEM and DEM modifies (adds/subtracts) the chromosome per fours loci at least, whereas CSM mutates per ones loci. So, to mutate 5% of the chromosome with 20 genes (80 loci) means to modify only 4 loci, which is achievable by applying one ANEM or one DEM procedure or applying CSM four times. In general, the behavior of the chromosome’s length (circuit size) during evolution corresponds to “oscillating length genotype strategy” proposed in [4], where the chromosome’s length can grow-up as well as short in size down. Getting the cir-batch-file from Block 2 (ES block), the Block 3 starts PSPICE, simulate and saves the results in out-file. PSPICE is utilized in non-interactive batch simulation mode. Block 4 contains the fitness function. It reads all chromosomes one by one from out-file, evaluates them assigning the fitness, selects the best S%, ranges them and sends the results to the Block 2. design of the first subcircuit, the second task was the design of both the first and the second subsicruts, the third task was a design of the first, the second and the third subcircuits and so on. Finally, the 8-th task was a design of all 8 subcircuits that is the whole Voltage Distributor circuit. For each task the new fitness function was introduced, that incrementally counted the fitness of all subcircuites evolved at the time. 3.4 Targeted circuit and the incremental evolution The main advantage of such the approach was the possibility to start the evolution of the next subcircuit (i.e. the 3-rd) based on the reuse of the previously evolved subcircuits (i.e. the 1-st and 2-nd). Due to the similarity of functions that subcircuits are going to perform, the evolution’s task (except the first subcircuit) was just to reprocess the previously evolved sibcircuits to the new subcircuit with a new pass band. There are two types of substructure reuse that we implied in the frame of this work. The first one is one of the mutations (SRM) applied to chromosomes using as substructures the fragments of successful chromosomes. Another kind of reuse was applied during incremental in between the transition from one subcircuit to another using as substructures the whole subcircuits evolved in previous substages. If the place for the first substructure inside the circuit is randomized, the place for the second one is definite: between source and load resistors on Figure 1. The general view of the N-output Voltage Distributor is presented on Figure 2, where in our case N=8. As an input signal for targeted circuit we took the piecewise voltage form starting from 0V, going up to 5V for 3.5sec and down to 0V for last 1.5sec. (Figure 4.). The task for each output was working in filter-like mode that is to pass the input signal that located within particular voltage band, saving the form of the input signal. That is, the band-pass width for each of the output was the same and equaled to 0.625V: the 1-st output passed the only voltages from 0 to 0.625V), the 2-nd output passed the only voltages from (0.625-1.25V), the 3-rd band-pass was (1.25-1.875V) , the 4-th was (1.875-2.5V), the 5-th was (2.5-3.125V), the 6-th was (3.125-3.75V) , the 7-th was (3.75-4.375V) and finally the 8-th was (4.375-5V). The summary of transient analysis at input and eight output pins of the targeted ideal 8-out Voltage Distributor is presented on Figure 4. As could be seen, the graph on Figure 4 must exactly repeat the form of the input piecewise signal. As mentioned above, the incremental evolution was introduced for design of 8-output Voltage Distributor. The fitness function were incremented each time whenever the current task was fulfilled. Totally 8 tasks corresponding to 8 subcircuits were set. Each subcircuit was responsible to get the incoming signal and to provide the outcoming signal to the corresponding output. If the first task was a Figure 4. The united transient analysis of potential at input and eight output pins of the targeted 8-out Voltage Distributor. 3.5 Fitness function and experiment implementation The dynamic fitness function scheduled to each incremental substage as a simple sum of the fitness values of all subcircuits evolved at the time. The final fitness function of the 8-output Voltage Distributor was i 8 F= F i , where Fi is a fitness value of the i 1 subcircuit i that calculated by the following way: we made the OrCAD PSPICE simulator to perform transient analysis at each output for 5 seconds at 81 equidistant time-points; a fitness value was set to the sum, over these 81 fitness cases of the absolute weighted deviation between the target value and the actual output value voltage produced by the circuit; the fitness penalized the output voltage by 10 if it was not within 50% of the target voltage value. The smaller the fitness value, the closer the circuit to the target. The termination criteria for the whole circuit was the fitness value was not improve over 20 consecutive generations, or if the best subcircuit exceeded 100 components. The condition for stopping the evolution of current subcircuit and getting to another was whether fitness exceeds the fitness threshold (0.05) or the generation number exceeds 200. The Evolutionary Strategy with linear representation and oscillating length genotype was utilized. 1%-selection scheme was applied that is S=1% of the best chromosomes were chosen for the next generation. Being chosen for the next generation each chromosome contributed 100 new chromosomes for the next population, thus, totally 1% of the selected chromosomes generated 100% population of the next generation. The evolutionary strategy is deserved the name of the simplest evolutionary algorithm, because it doesn’t content the crossover operation: all the offspring chromosomes are identical to a correspondent parent. A static mutation rate of 5% was allowed to apply to each chromosome by one of the mutation instruments described in subsection 3.3. Population size of 30,000 chromosomes was set. We used 5 PCs with Intel Core 2 Duo/2GHz processor running at the same time independently from each other. The results presented in the next section are the best out of the 5 runs for each case with different seeds for the random number generator. 4 Experimental Results The average time of the evolution of the 8-out Voltage Distributor was 344 hours, which is about 43 hours per subcircuit. The best-of-run circuit (Figure 5) appeared at 629-th generation and had 138 components (embryo excl.), among which 38 resistors, 8 capacitors, 7 inductors, 46 NPN transistors and 39 PNP transistors, with the best overall fitness 1.757. Table 2 highlights the detailed information per incremental substage: the best fitness, the component number of the evolved subcircuit and the successful generation number. The most ideal signal with fitness 0.028 was provided by out-pin No.2 that responsible for band 0.625V-1.25V; the worst reply with fitness 0.797 was at the out-pin No.7 in band 3.75V4.375V. Figure 6A shows the transient reply of the circuit for the incoming piecewise signal. Table 2. The summary of evolved 8-out Voltage Distributor and its composed subcircuits. Fitness Component Generation No succeed Subcircuit 1 0.095 10 76 Subcircuit 2 0.028 22 132 Subcircuit 3 0.174 16 110 Subcircuit 4 0.323 23 37 Subcircuit 5 0.049 14 26 Subcircuit 6 0.200 23 107 Subcircuit 7 0.797 22 104 Subcircuit 8 0.089 8 37 Total 1.757 138 629 To verify that circuit we had got worked properly we applied the different arbitrary signals to it. Figure 6B shows the more complicated piecewise signal and the transient reply at outputs. Figure 6C shows the arbitrary sinusoidal signal applied and the transient reply of the circuit. As could be visually noticed each particular subcircuit gives accurate replies throughout the different examples, what enables us to assume that the relative fitness of each of the subcircuit as well as the whole circuit less of all depends on the characteristics of the incoming signal. 5 Conclusion In this paper we described the application of the ES to the design of analog multi-output circuit, namely 8-output Voltage Distributor. To succeed with the target we utilized the linear representation, oscillating length genotype strategy, four types of mutation including the substructure reuse and the incremental evolution together with the dynamic fitness function that led us to the universal Voltage Distributor circuit with 8 outputs and with the largest component number for evolved analog circuits 138. The technique described is plain with simple algorithm that could be easily reconstructed. R0 1.5V R1 1.8k 270K Qn6 Qp0 Rl1 Qp1 Rs1 Qn0 V_OUT_1 15V Qn2 Qn4 10 1.5V 30 R2 9.4k Qn3 15V C1 2.7E-5 C0 33n 1.5V R3 1.8k Qp7 Qp2 R8 390 Qp4 R18 2.7E+7 1.5V Qp3 Qn5 Qn8 Qp6 R7 Qp9 1.5V 15V Qn7 30 Qn10 R4 R10 Qn14 1E+3 R5 15V C2 1.5V 3.9n C3 39n Qp13 1.5V 3.9E+4 R9 47 Qp10 1.2E+5K 1.5V Rl3 Qn12 Qp14 30 Qp11 Qn11 R19 1E+5 R37 1E+5 10 Qn13 15V 15V 1.5V L1 2.7M Qn20 R13 Qn17 Qp18 Qn15 Rl4 R16 12K 30 R17 82K R14 1E+5 15V Qp16 Qn18 R12 L0 Qn16 C4 2.7E-3 1.5V Qn19 3.3K 2.7M Qp17 Qp15 R20 68K 15V 1.5V R15 56K Qp37 1.5V R23 470 V_OUT_4 10 1.5V R11 1.8K V_IN Qn45 Qp19 12K Rs4 V_OUT_3 Qp12 15V Qn28 V_OUT_2 10 150K Qp5 15V Qn9 Rs3 Rl2 Qp8 1.5V Rs2 L5 L4 0.68 56M Rs5 1.5V Qn22 Qn23 30 Rl5 10 Qp21 15V V_OUT_5 Qn25 R21 1.8K Qn21 1.5V Qn24 Qp22 Qp20 1.2K R22 15V R27 1.2K L6 Qn26 15V 68M R24 1.8K 1.8E-4 C6 R26 180 15V Rs6 1.5V Qn29 C7 27n Qp23 Qp27 Qn27 30 Qn30 10 R28 180K Qp29 Qn36 15V Qp25 V_OUT_6 1.5V Qn31 Qp24 Rl6 Qp35 R29 18K Qp26 R25 68 Qn47 15V 15V Rs7 30 R31 2.2K 15V Qp30 Qp33 Qp32 Qn37 Qn35 Qp34 Qn33 1.5V Qn39 Qp31 Qn34 1.5V 15V R33 2.2K R35 1.5V 1E+9 R30 820 Qn41 15V Rl7 V_OUT_7 Qn38 1.5V Qn42 Qn40 15V R32 4.7K 1.5V 10 R34 C5 82n 1.5K Qp39 15V Qn43 Qp38 Qn46 L3 0.33 Rl8 1.5V Rs8 Qn44 15V L2 6.8M Qp36 30 15V R36 18 Figure 5. The evolved 138-component 8-output Voltage Distributor 10 V_OUT_8 A B C Figure 6. The summary of transient analysis at input and outputs of the 8-out Voltage Distributor. A-the input signal is a piecewise signal used in evolution, B-the input signal is an arbitrary piecewise signal applied for the circuit verification, C-the input signal is an arbitrary sinusoidal signal applied for the circuit verification 6. References [1] [2] [3] [4] [5] [6] Koza J.R., Genetic Programming II: Automatic Discovery of Reusable Programs, MA: MIT Press, Cambridge, 1994. Koza J.R., Bennett III F.H., Forrest H, Lohn J, Dunlap F., Andre D., and Keane M.A., “Automated synthesis of computational circuits using genetic programming”, IEEE Conference on Evolutionary Computation, NJ: IEEE Press, Piscataway, 1997, pp. 447–452. Mydlowec W., and Koza J.R, “Use of time-domain simulations in automatic synthesis of computational circuits using genetic programming”, Late Breaking Papers at the 2000 Genetic and Evolutionary Computation Conference, Las Vegas, Nevada, 2000, pp. 187 - 197. Zebulum R.S., Pacheco M.A., Vellasco M., “Comparison of different evolutionary methodologies applied to electronic filter design”, IEEE Conf. on Evolutionary Computation, NJ: IEEE Press, Piscataway, 1998, pp. 434439 Zebulum R S.., Stoica A., Keymeulen D., “Experiments on the Evolution of Digital to Analog Converters”, IEEE Aerospace Conference, Big Sky, Montana, USA Manhattan Beach, CA, 2001, Published in CD Lohn J.D., Colombano S.P., “Automated Analog Circuit Synthesis using a Linear Representation”, The 2nd International Conferene on Evolvable Systems: From Biology to Hardware, Springer-Verlag, Berlin, 1998, pp.125- 133 [7] Lohn J.D., Haith G.L., Colombano S.P., and Stassinopoulos D., “A Comparison of Dynamic Fitness Schedules for Evolutionary Design of Amplifiers”, Proceedings of the NASA/DoD Workshop on Evolvable Hardware, IEEE Computer Society, Los Alamitos, CA, U.S.A., 1999. pp. 87-92. [8] Mattiussi C., Floreano D., “Analog Genetic Encoding for the Evolution of Circuits and Networks”, IEEE Trans. on Evolutionary Computation. 2007, vol. 11, pp. 596-607 [9] Sapargaliyev Y., Kalganova T.G., “On Comparison of Constrained and Unconstrained Evolutions in Analogue Electronics on the Example of "LC" Low-Pass Filters”, IEICE transactions on Electronics, Vol.E89-C No.12 2006, pp.1920-1927 [10] Sapargaliyev Y. and T. Kalganova, 2009, “Evolution of Analogue Computational Circuits Using Evolutionary Strategy”, submitted to IET Circuits, Devices & Systems, Manuscript ID: CDS-2009-0252. [11] Langeheine J., Meier K., Schemmel J., “Intrinsic Evolution of Analog Electronic Circuits Using a CMOS FPTA Chip”, The 5th Conf. on Evolutionary Methods for Design, Optimization and Control (EUROGEN 2003), Barcelona, Spain, IEEE Press, 2003, 87/88 Published on CD: ISBN: 84-95999-33-1. [12] Feng W., Yuanxiang L., Kangshun L., and Zhiyi L., “A New Circuit Representation Method for Analog Circuit Design Automation”, IEEE World Congress on [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] Computational Intelligence, IEEE Press, Hong Kong, 2008.. Goh C., Li Y., “GA automated design and synthesis of analog circuits with practical constraints”, The Congress on Evolutionary Computation, Vol. 1, 2001, pp. 170-177 Ando S., Iba H., “Analog Circuit Design with a Variable Length Chromosome”, Congress on Evolutionary Computation, IEEE Press, 2000, pp.994-100 Grimbleby J.B., “Hybrid genetic algorithms for analogue network synthesis”, Congress on Evolutionary Computing (CEC99), Washington USA, 1999, pp. 1781-1787 Fan Z., Hu J., Seo K., Goodman E., Rosenberg R., Zhang B., “Bond Graph Representation and GP for Automated Analog Filter Design”, Genetic and Evolutionary Computation Conference Late-Breaking Papers, ISGEC Press, San Francisco, 2001, pp.81-86 Hu J., Zhong X., Goodman E., “Open-ended Robust Design of Analog Filters Using Genetic Programming”, Genetic & Evolutionary Computation Conference (GECCO), ACM Press, Washington, DC, 2005, Vol. 2, pp.1619-1626 Dastidar, T.R., Chakrabarti, P.P., Ray, P., “A synthesis System for Analog Circuits Based on Evolutionary Search and Topological Reuse”, “IEEE Trans. on Evolutionary Computation”, Vol. 9, Issue 2, 2005, pp. 211 – 224 Sripramong, T., Toumazou, C., “The invention of CMOS Amplifiers Using Genetic Programming and Current-flow Analysis”, IEEE Trans. on Computer-Aided Design of Integrated Circuits and Systems, 2002, Vol. 21, Issue 11, pp.1237 – 1252 Zhaohui G., Zhenkun Y., Gaobin L., and Min J., “Automatic Synthesis of Practical Passive Filters Using Clonal Selection Principle-Based Gene Expression Programming", Lecture Notes in Computer Science, Springer Berlin / Heidelberg, ISSN 0302-9743 (Print) 1611-3349 (Online), Volume 4684, 2007. S. J. Chang, H. S. Hou, Y. K. Su, “Automated Passive Filter Synthesis Using a Novel Tree Representation and Genetic Programming”, IEEE Trans. on Evolutionary Computation, 2006, vol. 10, pp. 93-100. Das A., Vemuri R., "An Automated Passive Analog Circuit Synthesis Framework using Genetic Algorithms," IEEE Computer Society Annual Symposium on VLSI (ISVLSI '07), 2007, pp. 145-152, Shibata, H.; Fujii, N., “Automated Design of Analog Computational Circuits Using Cell-based Structure Circuits and Systems”, ISCAS 2002. IEEE International Symposium, Volume 2, 2002, pp. II-53 - II-56 vol.2 X. Xia, Y. Li, W. Ying, L. Chen, “Automated Design Approach for Analog Circuit Using Genetic Algorithm”, Lect. Notes Comput. Sci, 2007, 4490, pp. 1124–1130 Kim K.J., Wong A., Lipson H., “Automated Synthesis of Resilient and Tamper-Evident Analog Circuits without a [26] [27] [28] [29] [30] [31] Single Point of Failure,” Genetic Programming and Evolvable Machines (online). Aplaydin, G., et al., “An Evolutionary Approach to Automatic Synthesis of High-Performance Analog Integrated Circuits”, IEEE Trans. Evol. Comp. 3, 2003 pp. 240 – 252 Kruiskamp W., Leenaerts D, “Darwin: CMOS Opamp Synthesis by Means of a Genetic Algorithm” Proc. 36th Design Autom. Conf. 1995. Kalganova T., “Bidirectional Incremental Evolution in Evolvable Hardware,” 2nd NASA/DoD Workshop Evolvable Hardware, 2000, pp. 65–74. Kalganova T., “An Extrinsic Function-Level Evolvable Hardware Approach”. Third European Conference on Genetic Programming, EuroGP2000, Springer-Verlag, Edinburgh, UK, 2000, vol. 1802, pp. 60–75. Sekanina L., Bidlo M., “Evolutionary Design of Arbitrarily Large Sorting Networks Using Development” Genetic Programming and Evolvable Machines, Vol. 6, No. 3. , 2005, pp. 319-347. Guoliang H., Naixue X, Vasilakos A.V., Yuanxiang L., Zhongzhi S., “Automated Design of Logic Circuits with a Increasable Evolution Approach”, 11th IEEE International Conference on High Performance Computing and Communications, Vol.00, ISBN:978-07695-3738-2 IEEE Computer Society Washington, DC, USA, pp. 206-213