Language：English   Publishing type：Research paper (international conference proceedings)

Language：English   Publishing type：Research paper (international conference proceedings)

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)

DOI： 10.1587/nolta.9.268

CiNii Article

Other Link： https://ci.nii.ac.jp/naid/130006602774

Language：English   Publishing type：Research paper (international conference proceedings)

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)

CiNii Article

Other Link： https://ci.nii.ac.jp/naid/110009996023

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)

CiNii Article

Other Link： https://ci.nii.ac.jp/naid/110009996024

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)

In order to develop large-scale nonlinear dynamical systems using CMOS integrated circuits, we propose a core circuit for coupled map lattice (CML) models. The characteristics of the core circuits in the lattice on a chip are not generally equal, which is caused by CMOS device mismatches, including parasitic capacitance and wiring resistance. The proposed circuit solves this problem; it compensates for a DC offset voltage variation by holding it at a capacitor, and also for current variation by adjusting the bias voltage of a current source automatically so as to bring the current close to a target value. The proposed core circuit has been designed and fabricated using TSMC 0.25 µm CMOS technology. The measurement results using the fabricated circuit have shown that the bit precision is more than 8 bits, even if there is a DC offset voltage of 100 mV or a bias-voltage change of 100 mV in a switched current source.

Other Link： https://ci.nii.ac.jp/naid/130005102329

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)

We propose a CMOS circuit that implements a chaotic spiking oscillator model, which acts as a filter of spike trains. This model is a phase oscillator that outputs a spike pulse at the timing with a predefined phase value, and transforms its phase value with a nonlinear transformation function at the timing of spike inputs. This model uses the input-spike interval as a bifurcation parameter, and outputs various spike-train patterns including non-output states. The proposed circuit for this model expresses the phase state value by charges stored at a capacitor charged up with a constant current source. We have designed and fabricated the proposed circuit using a standard CMOS integrated circuit technology, and have evaluated the fabricated circuit as a spike-train filter. We show the measurement results for verifying the circuit operation.

CiNii Article

Other Link： https://ci.nii.ac.jp/naid/110010002094

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)

DOI： 10.1587/nolta.6.570

CiNii Article

Other Link： https://ci.nii.ac.jp/naid/130005102329

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)

e experimentally study strange nonchaotic attractors (SNAs) and chaotic attractors by using a nonlinear integrated circuit driven by a quasiperiodic input signal. An SNA is a geometrically strange attractor for which typical orbits have nonpositive Lyapunov exponents. It is a difficult problem to distinguish between SNAs and chaotic attractors experimentally. If a system has an SNA as a unique attractor, the system produces an identical response to a repeated quasiperiodic signal, regardless of the initial conditions, after a certain transient time. Such reproducibility of response outputs is called consistency. On the other hand, if the attractor is chaotic, the consistency is low owing to the sensitive dependence on initial conditions. In this paper, we analyze the experimental data for distinguishing between SNAs and chaotic attractors on the basis of the consistency.
Strange nonchaotic attractors (SNAs) often appear in dynamical systems driven by a quasiperiodic signal. An SNA is a geometrically strange attractor for which typical orbits have nonpositive Lyapunov exponents. In fact, typical orbits are insensitive to initial conditions under a common quasiperiodic signal. Owing to their characteristics reminiscent of both quasiperiodic order and chaos, SNAs have attracted the attention of researchers from both theoretical and experimental perspectives. Conventionally, the information dimension is often employed to distinguish between SNAs and chaotic attractors in experiments. However, using the information dimension for the experimental distinction between these types of attractors is difficult as the estimation of the information dimension is highly sensitive to noise, and requires rather long time series. Recently, Ngamga et al.1 proposed a method for distinguishing between SNAs and chaotic attractors, which utilizes the consistency property of SNAs. Consistency here means that a nonlinear system shows the same response to the same input signal after some transient time, regardless of the initial conditions. In the method proposed by Ngamga et al., the determinism for a cross-recurrence plot of two response time series to the same input signal is used as a consistency measure. However, to our knowledge, there is no research paper on using their cross-recurrence method to experimentally distinguish between SNAs and chaotic attractors. In this study, we evaluated the consistency of a system by using the zero-delay normalized cross-correlation and Ngamga et al.'s cross-recurrence methods. By combining spectrum analysis and evaluation of consistency, we showed that SNAs and chaotic attractors can be distinguished more precisely as compared to conventional methods.

DOI： 10.1063/1.4804181

Other Link： https://aip.scitation.org/doi/10.1063/1.4804181

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)

In order to develop large-scale coupled nonlinear dynamical systems using CMOS integrated circuits, we propose a threshold-coupled map array circuit that is robust to CMOS device mismatch. We have already proposed a voltage- and a current-sampling mode circuits which can achieve arbitrary analog nonlinear dynamics in the time domain by using pulse width/phase modulation (PWM/PPM) signals. Both circuits have advantages of robustness to parameter mismatches of CMOS circuit elements and facilitation of weighted summation of connected states, respectively. These advantages are important for developing a large-scale coupled array circuit. In this study, we employ a circuit architecture having the advantages of these sampling mode, and propose a circuit that is robust to voltage-shift dispersion of CMOS analog buffers. We show this robustness of the proposed circuit by SPICE circuit simulation.

CiNii Article

Other Link： https://ci.nii.ac.jp/naid/110009728129

Language：English   Publishing type：Research paper (scientific journal)

Torus-doubling bifurcations typically occur only a finite number of times. It has been assumed that torus-doubling bifurcations in quasiperiodically forced systems are interrupted by the appearance of strange nonchaotic attractors (SNAs). In the present Letter, we study a quasiperiodically forced noninvertible map and report the occurrence of a torus-doubling process via SNAs. The mechanism of this process is numerically clarified. Furthermore, this process is experimentally demonstrated in a switched-capacitor integrated circuit.