A circuit for computing a tracking error signal digitally. Under control of appropriate timing, input RF signals are latched in successive latches, and outputs of the latches are compared. The latch (9) whose output is D/A converted as a tracking error signal is controlled by suitable logic (25) to latch an output of a preceding latch (8), that output being used to provide input to the logic (25) through a threshold circuitry which includes adders (21,22) and comparators (14,15). The circuit takes advantage of servo patterns on surfaces of disks, particularly optical disks, to provide track count and on-track status. The digital approach removes the necessity for using capacitors or other types of sample-and-hold circuitry, and for controlling offset values.