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

82 CHAPTER 3
Over an address decoder matrix each pixel can be accessed individually by
activating the corresponding row select and column select transistor switches. In
this way each in-pixel source follower transistor can selectively be switched into a
complete 2 stage source follower stage and change the output signal by it’s light
dependent conductivity.
CMOS APS, however, is not necessarily restricted to photodiodes; the light
sensitive areas could also be realized as photogates [FOS] or even some CCD
structures (see Chapter 5). APS only describes the principle of realizing active
pixels, that means pixels with an active stage (buffer transistor).
What has made CMOS APS a serious competitor on the imager market is above all
the (more or less) unmodified use of relatively cheap, widely available CMOS
processes. Not only are they available for prototyping services, enabling widely
spread research activity in this area, but they also benefit from the steady process
development driven by other industries (mainly computers).
For the customer, essential arguments for using CMOS sensors instead of CCD is
their low price, high functionality (digital cameras on a chip), low voltage (1.2V-5V)
and extremely low power consumption (20mW) [EMM]. Also they do not require
elaborate driving electronics but can be directly controlled by microcontroller, DSP
or FPGA logic.