Basler acA2000-165, User Manual

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AW00123402000 Camera Functional Description
Basler ace USB 3.0 41
4 Camera Functional
Description
This chapter provides an overview of the camera’s functionality from a system perspective. The
overview will aid your understanding when you read the more detailed information included in the
later chapters of the user’s manual.
4.1 Overview (acA640-90, acA640-120,
acA1300-30, acA1600-20)
The camera provides features such as a global shutter and electronic exposure time control.
Exposure start and exposure time can be controlled by parameters transmitted to the camera via
the Basler pylon API and the USB 3.0 interface. There are also parameters available to set the
camera for single frame acquisition or continuous frame acquisition.
Exposure start can also be controlled via an externally generated "frame start trigger" (ExFSTrig)
signal applied to a camera input line. The ExFSTrig signal facilitates periodic or non-periodic frame
acquisition start. Modes are available that allow the length of exposure time to be directly controlled
by the ExFSTrig signal or to be set for a pre-programmed period of time.
Accumulated charges are read out of the sensor when exposure ends. At readout, accumulated
charges are transported from the sensor’s light-sensitive elements (pixels) to the vertical shift
registers (see Figure 25 on
page 42 ). The charges from the bottom row of pixels in the array are
then moved into a horizontal shift register. Next, the charges are shifted out of the horizontal
register. As the charges move out of the horizontal shift register, they are converted to voltages
proportional to the size of each charge. Each voltage is then amplified by a Variable Gain Control
(VGC) and digitized by an Analog-to-Digital converter (ADC). After each voltage has been amplified
and digitized, it passes through an FPGA and into an image buffer. All shifting is clocked according
to the camera’s internal data rate. Shifting continues in a row-wise fashion until all image data has
been read out of the sensor.
The pixel data leaves the image buffer and passes back through the FPGA to a controller where it
is assembled into data packets. The packets are then transmitted by bulk transfer via a USB 3
compliant cable to a USB 3 host adapter of the host PC. The controller also handles transmission
and receipt of control data such as changes to the camera’s parameters.
The image buffer between the sensor and the controller allows data to be read out of the sensor at
a rate that is independent of the data transmission rate between the camera and the host PC. This
ensures that the data transmission rate has no influence on image quality.