Operation And Features; Functional Description - Basler A101f User Manual

3 Operation and Features

3.1 Functional Description

The A101 area scan camera employs a CCD-sensor chip which provides features such as
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electronic exposure time control and anti-blooming.
Normally, exposure time and charge readout are controlled by values transmitted to the camera's
control registers via the IEEE 1394 interface. Command registers are available to set exposure
time and frame rate. There are also command registers available to set the camera for single
frame capture, multiple frame capture, and continuous frame capture.
Exposure start can also be controlled via an externally generated trigger (ExTrig) signal. The
ExTrig signal facilitates periodic or non-periodic start of exposure. When exposure start is
controlled by an ExTrig signal, exposure begins when the trigger signal goes low and continues
for a pre-programmed period of time. Accumulated charges are read out when the programmed
exposure time ends.
At readout, accumulated charges are transported from the sensor's light-sensitive elements
(pixels) to the vertical shift registers (see Figure 3-1). The charges from the bottom line of pixels
in the array are then moved into a horizontal shift register. As charges move out of the horizontal
shift register, they are converted to voltages which are proportional to the size of each charge.
Shifting is clocked according to the camera's internal data rate.
The voltages moving out of the horizontal shift register are amplified by an internal Variable Gain
Control (VGC) and then digitized by a 10 bit Analog-to-Digital converter (ADC). For optimal
digitization, gain and brightness can be programmed by setting command registers in the camera.
Since the IEEE 1394 bus can only handle 8 bit data, the two least significant bits from the ADC
are dropped.
The 8 bit pixel data leaving the ADC is transferred to an image buffer. From the buffer, the image
data is moved to a 1394 link layer controller where it is assembled into data packets that comply
with version 1.20 of the "1394 - based Digital Camera Specification" issued by the 1394 Trade
Association. The packets are passed to a 1394 physical layer controller which transmits them
isochronously to a 1394 interface board in the host PC. The physical and link layer controllers also
handle transmission and receipt of asynchronous data such as programming commands.
The image buffer between the sensor and the link layer controller allows data to be transferred out
of the sensor at a rate that is independent of the of the data transmission rate between the camera
and the host computer. This ensures that the data transmission rate has no influence on image
quality.
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BASLER A101
DRAFT
Operation and Features
3-1