Charge transfer devices having switchable blocking electrodes

Claim 1

A charge transfer device having a switchable blocking electrode comprising: a semiconductor layer of one conductivity type; means for permitting information in the form of packets of charge to be locally introduced into said semiconductor layer; read means for permitting the information to be read at another location in said layer; control electrodes at least on one side of said layer; said control electrodes connected to clock lines such that two adjacent electrodes are connected to different clock lines; said clock lines connected to a clock pulse generator for delivering multiphase clock signals by means of which electrical fields are capacitively generated in said semiconductor layer, with which fields the charge packets can be transferred to said read means along a channel in said layer in a direction parallel to said layer; at least one of said control electrodes being divided into two or more parts in a direction perpendicular to the direction of charge transfer; switching means present between at least one of said control electrodes or a divided part thereof and the respective clock line for permitting the application of a voltage which at one time is equal to a phase of the clock signal which together with the clock voltages on adjacent control electrodes ensures the transfer of a charge packet in the channel underneath said at least one control electrode and at another time is equal to a blocking voltage which prevents the transfer of a charge packet in the channel underneath said at least one control electrode; said switching means being constituted by a change-over switch having a master contact connected to said at least one control electrode, one contact connected to a terminal for the application of a blocking voltage and another contact connected to a clock conductor to which said at least one control electrode would be connected in the absence of the change-over switch; means for splitting the transfer channel into as many channel sections as there are parts into which said at least one control electrode is divided, each of the parts of said control electrode functioning as a control electrode for the channel section underneath it; said means for splitting the transfer channel comprising isolation diffusions each of which is located below the area between two adjacent parts of the divided control electrode, each of said parts partly overlapping the relevant isolation diffusion, and the isolation diffusions extending substantially in the direction of charge transfer; at least one sensing element arranged in front of the blocking electrode in the direction of the charge transfer and associated with the same channel as said blocking electrode, which sensing element is connected to a detector connected directly or indirectly to a comparator for comparing the magnitude of the signal appearing at the output of the detector with a reference signal, the output signal of the comparator being applied to a control input of said switching means either through or not through delay elements.