618
22 Light-to-Electricity Conversion
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
Fig. 22.39 a Three-phase CCD. Each pixel has three electrodes that can be switched independently (phases 1–3). b, e,
f Schematic of CCDs with four, two or one phase, respectively. c (t 1 ) Charge accumulated after light exposure. A lateral
potential well is formed along the row of pixels by the voltages at the three electrodes, e.g. P 1 = P 3 = 5 V, P 2 = 10,V.
(t 2 –t 7 ) transfer of charge, (t 7 ) has the same voltages as (t 1 ), the charge has been moved one pixel to the right. d, g, h
Timing schemes for 4-, 2- and 1-phase CCDs, respectively. From [1853]
22.3.9 Photodiode Arrays
An array of photodiodes is also suitable to create an image sensor. During illumination each diode
charges a capacitor that is read out with suitable electronics. Based on CMOS technology (cf.
Sect. 24.5.4), economic image sensors can be made (CMOS image sensors, CIS) [1859, 1860]. For a
long time they exhibited inferior performance to CCDs but progress in readout and noise suppression
has made them the image sensor of choice for many camera applications including the smart phone