  The equivalence between integral-chain differentiator and usual high-gain
differentiator is given under suitable coordinate transformation.
Integral-chain differentiator can restrain noises more thoroughly than usual
high-gain linear differentiator. In integral-chain differentiator, disturbances
only exist in the last differential equation and can be restrained through each
layer of integrator. Moreover, a nonlinear integral-chain differentiator is
designed which is the expansion of linear integral-chain differentiator.
Finally, a 3-order differentiator is applied to the estimation of acceleration
for a second-order uncertain system.
