Error rates of digital signals in charge transfer devices

Abstract

We calculate the probability of error in detecting digital signals transferred through a charge transfer device in the presence of incomplete charge transfer, random noise in the device, and detection uncertainty in the detector. The coefficient of incomplete charge transfer is assumed to be independent of charge-packet size, and both the device noise and detector noise are assumed to be Gaussian. Error probabilities for two-level and four-level codes are computed for the cases of both simple static and optimum dynamic detection. For rms detection voltage level fluctuations V d of the order of tenths of volts (much larger than the random noise fluctuations in the device), a very rapid increase in error probability (from ≍ 10−20 to ≍ 10−5) is found to occur for a very small (20 percent) change in V d . This indicates that detection level fluctuations will have to be held down to a few hundred millivolts at most. To achieve equal error rates with an error probability of about 10−14, V d for the detection of four-level codes will have to be about 3.5 times smaller than for two-level codes. Comparison of error probabilities under static and dynamic detection shows that in CTD's improved detection has a greater potential for reducing error rates than improved coding.