3D Time-of-flight distance measurement with custom - Universität ...

148 CHAPTER 5
When we implemented the 1-tap pixel realization, we considered implementing at
least point (1) (2-tap instead of 1-tap pixel), since it is obvious that the photocharge
that we currently dump with the 1-tap pixel corresponds exactly to the 180° shifted
sampling point. However, we preferred at that early time to implement the easiest
demodulation pixel in order to get a reliable demonstrator, rather than running the
risk of receiving non-functional devices from the foundry by trying to implement too
much functionality at a time.
storage 0°
Mod0°
PGM
Mod180°
storage 180°
CCDsep
storage 90°
Mod90°
PGM
Mod270°
storage 270°
0°/180°
90°/270°
Light sensitive
(detection and
demodulation)
Opaque (storage)
Figure 5.26 Two-photosite demodulation pixel: basic architecture.
The basic structure of the new pixel is illustrated in Figure 5.26. The pixel consists
of two light sensitive areas. Each of these areas is divided into two or three light
sensitive modulation gates (here a 3-gate realization is shown). During
demodulation/integration operation, the middle gate (if present) is kept at a fixed
potential and the outer modulation gates are modulated in a balanced manner.
Optically generated charge carriers are then distributed to the neighboring storage
gates, depending on the actual potential gradient under the modulation gates. The
storage gates are isolated from each other by an additional transportation gate. The
two modulation-gate-pairs within one pixel are operated with a relative phase
difference of 90°, so that the one pair integrates the in-phase component (1 st and
3 rd sampling point) and the other pair integrates the quadrature-phase component
(2 nd and 4 th sampling point respectively). Each gate within the pixel can be
controlled individually.