It uses correlation to determine the direction of motion. Phototransduction is performed by an integration based photocircuit using a photodiode. The image at one sampling time is digitized to a one bit image pattern and stored in latches. It is then correlated with the analog signal detected in the next sample using the architecture shown in Figure 3.2 . The digitization of the image to one bit in the latch branch is done for simplifying the design.
Multiplication is performed using a simple current mirror switched by the output of the latch.
The currents are summed by hard-wiring the outputs of all current mirrors.