  We investigate and report an experimental confirmation of zero-lag
synchronization (ZLS) in a system of three coupled time-delayed piecewise
linear electronic circuits via dynamical relaying with different coupling
configurations, namely mutual and subsystem coupling configurations. We have
observed that when there is a feedback between the central unit (relay unit)
and at least one of the outer units, ZLS occurs in the two outer units whereas
the central and outer units exhibit inverse phase synchronization (IPS). We
find that in the case of mutual coupling configuration ZLS occurs both in
periodic and hyperchaotic regimes, while in the subsystem coupling
configuration it occurs only in the hyperchaotic regime. Snapshots of the time
evolution of outer circuits as observed from the oscilloscope confirm the
occurrence of ZLS experimentally. The quality of ZLS is numerically verified by
correlation coefficient and similarity function measures. Further, the
transition to ZLS is verified from the changes in the largest Lyapunov
exponents and the correlation coefficient as a function of the coupling
strength. IPS is experimentally confirmed using time series plots and also can
be visualized using the concept of localized sets which are also corroborated
by numerical simulations. In addition, we have calculated the correlation of
probability of recurrence to quantify the phase coherence. We have also
analytically derived a sufficient condition for the stability of ZLS using the
Krasovskii-Lyapunov theory.
