Basler A400K, User Manual

Page: 53 / 176

Basic Operation and Features
Basler A400k 3-1
DRAFT
3 Basic Operation and Features
3.1 Functional Description
BASLER A400k area scan cameras employ a CMOS-sensor chip which provides features such
as an electronic rolling shutter and electronic exposure time control. Exposure time is controlled
either internally via an internal sync signal (free-run mode) or externally via an external trigger
(ExSync) signal. The ExSync signal facilitates periodic or non-periodic pixel readout.
In any free-run mode, the camera generates its own internal control signal and the internal signal
is used to control exposure and charge readout. When operating in free-run, the camera outputs
frames continuously.
When exposure is controlled by an ExSync signal, exposure time can be either level-controlled or
programmable. In level-controlled mode, charge is accumulated when the ExSync signal is low.
The rising edge of ExSync triggers the readout. In programmable mode, exposure time can be
programmed to a predetermined time period. In this case, exposure begins on the rising edge of
ExSync and accumulated charges are read out when the programmed exposure time ends.
At readout, accumulated charges move out of the light-sensitive sensor elements (pixels).
Moveout is clocked according to the camera's 50 MHz internal data rate. As the charges move out
of the pixels, they are converted to voltages proportional to the size of each charge.
The sensor has a column-parallel analog-to-digital converter (ADC) architecture that lets the array
of 2,352 ADCs on the chip digitize simultaneously the analog data from an entire line of pixels.
The analog data is converted into 10-bit digital pixel data by the 10-bit ADCs (shown in Figure
3-
1 on page 3-2). The digitized data is then stored in column parallel 10-bit ADC registers.
Now, the digitized pixel data is shifted in portions of 160 bits from the ADC registers to the output
registers and output in ascending numerical order from pixel 1 through pixel 2,352 and from the
first line through the last line via 16 output ports that each transmit 10-bit pixel data in parallel with
each cycle. Finally, the output data is reformatted and transferred out of the camera as shown
below:
• In the A402k, the data is reformatted to be output in two data streams in parallel (2 taps).
• In the A403k
,
the data is reformatted to be output in four data streams in parallel (4 taps).
• In the A404k
,
the data is reformatted to be output in four data streams in parallel (4 taps) or in
eight data streams in parallel (8 taps).
The 8 bit or 10 bit video data is transmitted from the camera to the frame grabber using a Camera
Link transmission format (see Section
2.5 for details). The camera can transmit video at an eight
bit depth or a ten bit depth.
For optimal digitization, gain and offset are programmable via a serial port.