Theory of Noise in Charge-Transfer Devices

Charge-transfer devices (CTD's), such as the bucket-brigade 1 (BB) and charge-coupled-device2 (CCD) shift registers, are currently of great interest. These devices consist of a chain of charge-storage elements along which charge packets are transferred from input to output. Noise accompanying each individual transfer of each charge 1211 packet will be introduced into each packet. It is the purpose of this article to calculate this noise and its cumulative effects on the output signal. Noise generated in solid-state devices has been treated extensively, 3-6 and this prior work will be of great assistance to us here. However, there are three major, significant differences between much of this prior work and the present treatment. 7 ' 8 The first difference arises from the nature of the transfer process.9 The usual treatments of noise discuss situations in which the (noiseless) currents, charge densities, conductances, etc. associated with the signal are timeinvariant. Under such conditions, the statistics of the noise are also time-invariant and the noise is said to be stationary. Stationary noise is readily treated in the frequency domain using spectral-density functions. Frequency-domain, linear-circuit analysis of equivalent circuits greatly facilitates the usual treatments. (Sometimes, as in mixer theory, periodic rather than time-invariant situations are considered, and frequency-domain analyses are still convenient.) In CTD's the situation is quite different. During the transfer of the charge from one storage region to the next, the (noiseless) currents, charge densities, conductances, etc.