Disclosed is focus control method for Delta-Sigma based image formation
devices in which a steering term and a focusing term of a delay formula are respectively
quantized, and corresponding two channels at both sides of the probe are synchronized
by a delay produced during dynamic focusing. During synchronizing the two channels,
two numeral values with equal absolute value but with opposite signs are respectively
inserted so as to eliminate extra noise the signals are after summing up, and controlling
common delay of the two channels is performed by same one controller. After summing
up the inserted two values, the dynamic aperture control of the Delta-Sigma based
image formation device can be effectively realized and noise during dynamic focusing
also is eliminated thereby achieving an ideal single bit output.
