Charge transfer efficiency in a buried-channel charge-coupled device at very low signal levels

A measurement of charge transfer efficiency (CTE) is described for a 256-element charge-coupled linear imaging device operated below room temperature and at a very low total charge level per charge packet, that is, at a level of approximately 1/20000th of saturation. This measurement was carried out at a register frequency near 15.75 kHz, the standard television-line frequency. CTE was measured by noting the dependence of the size of the principal charge packet upon the number of transfers. It was observed that at a dark current level of 4 electrons per packet and a photosignal level of 15 electrons the signal loss through approximately 250 transfers was 1/spl plusmn/5 electrons at the 50 percent confidence level. A signal-averaging technique was used to obtain this small probable error in the measurement.