Nonlinearity in automatic gain control (AGO systems is an interesting problem. AGC systems are different from general control systems

for nonlinearity i:

contained in the executors. For first order with constant signal amplitude

we analyze the nonlinear discrete systems by means of a state transition method and present graphically the process of state transition

or the dynamic process. For higher order and in the case of fluctuating signal amplitude

we make the AGC systems equivalent to a "standard" control system

which is easy to analyze. This equivalence is vaiid strictly for both discrete and continuous systems.We present a method of linearizing AGC systems

that is

we transform the AGC systems with serious nonlinearity into a linear system by using a logarithmic amplifier as a nonlinear corrector.At last

based on above analyses

two possible applications are presented. In one

the logarithm of signal amplitude is implemented digitally on the principle of A.GC. In the other

a proposition

with which a logarithmic amplifier is employed for open-loop gain control

is given.