  The discrete modeling of the Geiger-mode APD is considered. Results of
modeling and experimental measurements with the SiPM show that the known
formula for the charge of the avalanche pulse Q=dU*Cd underestimates its value.
In addition, it is seen from the dynamic of the avalanche multiplication that
the resistor Rq in photodiode, usually called a quenching resistor, in reality
fulfills only the restoring function. The SiPM restoring time, taken into
account the number of pixel N and the load resistance R, is T=Cd*(Rq+NR).
