14 February 2000
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Physics Letters A 266 2000 19–23
www.elsevier.nlrlocaterphysleta
A new class of chaotic circuit
J. C. Sprott
)
Department of Physics, UniÕersity of Wisconsin, Madison, WI 53706, USA
Received 30 November 1999; received in revised form 4 January 2000; accepted 4 January 2000
Communicated by C.R. Doening
Abstract
A new class of chaotic electrical circuit using only resistors, capacitors, diodes, and inverting operational amplifiers is
{
Ž. Ž.
described. This circuit solves the equation xqAxq xs Gx, where Gx is one of a number of elementary piecewise
¨˙
linear functions. These circuits are easy to construct and to scale over a wide range of frequencies. They exhibit a variety of
dynamical behaviors and offer an excellent opportunity for detailed comparison with theory. q 2000 Published by Elsevier
Science B.V. All rights reserved.
PACS: 05.45.Ac; 02.30.Hq; 02.60.Cb; 47.52.qj; 84.30.Ng
Keywords: Chaos; Electrical circuit; Operational amplifier; Jerk; Differential equations
After three decades of study, the sufficient condi-
tions for chaos in a system of autonomous ordinary
Ž.
differential equations ODEs remain unknown. For
continuous flows, the Poincare–Bendixson theorem
´
wx
1 implies the necessity of three variables and at
wx
least one nonlinearity. The Rossler attractor 2 is a
¨
standard example of such a system with a single
quadratic nonlinearity. Systems with one nonlinearity
can generally be written as a third-order ODE in a
single scalar variable, suggesting a means to catalog
wx
and quantify the complexity of such systems 3 . In
this scheme, the Rossler system is relatively compli-
¨
wx
cated 4 , and the algebraically simplest dissipative
wx
quadratic form 5 is
{
2
xsyAxq x y x,1
Ž.
¨˙
which exhibits chaos for values of A equal to or
slightly greater than 2.017. Systems of the form
)
Fax: q1-608-2627205.
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E-mail address: sprott@juno.physics.wics.edu J.C. Sprott .
{
Ž. Ž
xs Fx, x, x have been called jerk equations time
¨˙
. wx
derivative of acceleration 6 .
The discovery of this and other such simple sys-
wx wx
tems 7 prompted a search 8 for similar examples
in which the quadratic nonlinearity is replaced by
NxN or another elementary piecewise linear function.
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2
Although Eq. 1 with N xN in place of x does not
˙˙
appear to have chaotic solutions for any A and initial
wx
conditions, chaos was found 9 in the system
{
xsyAxy xqNxNy12
Ž.
¨˙
Ž.
with A equal to or slightly greater than 0.6. Eq. 2
is a special case of the more general system
{
xq Axq xs Gx,3
Ž. Ž.
¨˙
Ž.
where Gx is a nonlinear function with the proper-
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ties discussed below. Integrating each term in Eq. 3
reveals that it is a damped harmonic oscillator driven
by a nonlinear memory term involving the integral of
Ž.wx
Gx 4 . Such an equation often arises in the feed-
back control of an oscillator in which the experimen-
0375-9601r00r$ - see front matter q 2000 Published by Elsevier Science B.V. All rights reserved.
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PII: S0375-9601 00 00026-8