Output circuit for charge transfer transversal filter

A transversal filter comprising

• a substrate of semiconductor material of one conductivity type,
• a first plurlity of electrodes insulatingly overlying said substrate, each split into a first and a second part with a gap therebetween,
• a second plurality of electrodes insulatingly overlying said substrate, each spaced between adjacent electrodes of said first plurality, said first and second pluralities of electrodes forming a plurality of stages of a shift register,
• means for connecting the first parts of said electrodes of said first plurality to a first conductive line,
• means for connecting the second parts of said electrodes of said first plurality to a second conductive line,
• means for introducing packets of charge representing successive samples of an analog signal into said shift register,
• charge clocking means to effect the transfer of charge from storage region to storage region underlying said first and said second pluralities of electrodes including means for applying a first fixed voltage to said first plurality of electrodes and for applying a first pulsating voltage to said second plurality of electrodes, said first fixed voltage being applied to said first and said second lines, said first pulsating voltage having a predetermined periodicity,
• a plurality of transfer electrodes, each insulatingly overlying a respective adjacent pair of electrodes of said first plurality and said second plurality of electrodes, alternate ones of said transfer electrodes being interconnected to form a first plurality and a second plurality of transfer electrodes, means for applying a second fixed voltage to said first plurality of transfer electrodes, means for applying a second pulsating voltage to said second plurality of transfer electrodes, means for synchronizing said first and second pulsating voltages, said second fixed voltage being of a value in relation to said first fixed value of voltage and the levels of said second pulsating voltage being set in relation to the levels of said first pulsating voltage to enable charge to be transferred from storage regions of said second plurality to storage regions of said first plurality under the control of the level of potential on said second plurality of transfer electrodes,
• differential sensing means connected to said first and second lines for detecting a difference in signal on said lines in response to the transfer of charge from storage regions underlying said second plurality of electrodes to storage region underlying said first plurality of electrodes for obtaining a sum of weighted samples of said analog signal including
• a high gain differential amplifier having a pair of input terminals and an output terminal, one of said input terminals being an inverting input terminal and the other being a non-inverting terminal, a first capacitor, said inverting terminal connected to said output terminal through said first capacitor and also connected to said first line, said non-inverting terminal connected to said second line,
• a source of said first fixed voltage,
• first and second diodes, said first diode connected between said first line and said output terminal, said second diode connected between said second line and said source, said first and second diodes being poled so as to be rendered conductive periodically during a period prior to transfer of charge from the storage regions underlying said second plurality of electrodes to the storage regions underlying said first plurality of electrodes and rendered non-conductive during a time including the time of transfer of charge from the storage regions underlying said second plurality of electrodes to the storage regions underlying said first plurality of electrodes in response to said second pulsating voltage on said second plurality of transfer electrodes capacitively coupled to said first plurality of electrodes,
• whereby each of said lines is charged to substantially the value of said first fixed voltage of said source periodically prior to the transfer of charge into the storage regions underlying said first plurality of electrodes and thereafter said lines are isolated from said source, and charge periodically transferred from the storage regions underlying said second plurality of electrodes to storage regions underlying said first plurality of electrodes induces different voltages on said lines and causes the voltage of the inverting terminal to follow the voltage of the non-inverting terminal by virtue of the feedback through said first capacitor and a total charge is supplied to said first capacitor which is proportional to the difference in charge delivered to said lines during said transfer of charge, said total charge appearing as a change in voltage at said output terminal.