Linearity of electrical charge injection into charge-coupled devices

This has been studied by measuring the generated higher harmonic components of a sinusoidal input. Results obtained with various injection methods and device geometries have been compared. Best results, with all harmonic components more than 40 dB below the fundamental, have been obtained for surface channel devices with a potential equilibration method in which the signal is applied to a second input gate, while the first input gate is held at a d.c. reference potential. It is concluded that this version of the potential equilibration method is readily adoptable for CCDs with any number of phases and that, if the active gate areas are suitably enlarged, harmonic distortions of less than -60 dB may be expected.