Feed forward due to barrier modulation in charge-coupled devices

A new type of signal degradation, namely feed forward, is shown to exist in charge-coupled devices. This arises because of barrier modulation due to signal charge and the presence of surface states. Feed forward results in a pulse coming out earlier than the main signal pulse. The magnitude of the feed forward pulse was found to be as high as 0.5 percent of the signal charge for a 24½ bit, CCD delay line. Computer calculations have been performed to quantify the effect for the structure. Results obtained with a special clock for different clocking parameters have been explained, based on the existing model of emission of charge from the surface states.