Surface potential equilibration method of setting charge in charge-coupled devices

A method of setting charge in a charge-coupled device (CCD) is described whereby the input diode is suitably pulsed and an amount of charge is retained in a potential well under the first transfer electrode. It is shown that, within limits defined by the operating potentials of the device, the sizes of the generated charge packets are linearly dependent on the voltage difference between the first transfer electrode and the input gate. They are also independent of threshold voltage. The method has important applications in all CCD's where it is necessary to obtain a linear low noise charge input that is uniform from one device to another. The linearity has been demonstrated with a 64-element CCD which with a sinusoidal input shows second and third harmonics to be 40 dB down from the fundamental. Measured rms input noise was above the minimum theoretically achievable value but was still 80 dB down from the peak signal level. The electrode area was 2000 μm
²
. For a comprehensive review on CCD's and input circuits, see [10].