Figure 5 from D. Reuter et al., 2008: "Ralph: A Visible/Infrared Imager for the New Horizons Pluto/Kuiper Belt Mission"
Time-Delay Integration (TDI)
Illustration of TDI in operation. In step 0, a target is about to enter the field of view of a TDI array. In step 1, the image of the target has moved a single pixel width into the first row of the array. In step 2, the charge is transferred to the second row of the array and integration continues. A new target has moved into row 1. The next charge transfer occurs when the image of the target has moved another row. In step 32, the target has moved 32 rows, with the charge being transferred each time the image moves another row. At the next charge transfer, the charge in row 32 is transferred to a serial column for pixel readout.