Bucket-brigade shift-register operation-exact correlation between experimental data and a computer model

A detailed analysis of the IGFET bucket brigade is presented covering its low frequency, midfrequency, and high frequency performance. Attention is first focused on those factors giving rise to performance limits in the midfrequency range of operation. The concept of an optimized threshold voltage V/SUB TO/ is introduced and related to the array parameters. It is shown that if the threshold voltage V/SUB T/ of the IGFET's in the array are below V/SUB TO/, then transfers become incomplete. The effect that substrate resistivity has on the array performance is also considered. It is shown that conventional IGFET channel length modulation is not the only factor to be considered in analyzing this performance limit. It is shown that high frequency and low frequency limits can be accounted for using conventional IGFET theory. Calculations resulting from a simple model that includes all these effects are presented. They are shown to correlate exactly with the experimental data from operating arrays.