BCON for LVDSハードウェア設計ガイド#
Identifiers such as X1, XCLK, CC0, or I2C_SDC refer to the pin names given in your camera topic. You can find your camera topic in the "Models" section.
Data Transmission (X0, X1, X2, X3, XCLK)#
BCON for LVDS uses four data lanes (X0 through X3) and one clock line (XCLK) to transmit image data from the camera to the image processing unit.
During data transmission, signal reflections can be a major cause of bit errors. Every signal change in the transmitter launches a wave that travels to the receiver. If the termination resistor at the other end of the trace matches the impedance of the differential trace, it consumes most of the energy of the wave.
Therefore, both the differential traces and the termination resistors must have an impedance of 100 ohm. If they don't match the target impedance, the reflected wave can disturb the original signal and cause bit errors.
Design Recommendations for Data Transmission#
Printed Circuit Board (PCB)#
- Design the PCB to have a differential impedance of 100 ohms. If this is not possible, make the traces between the connector and the receiver as short as possible.
- Run the differential traces as close as possible, but leave a gap of at least three trace widths between the individual pairs.
- Ensure that the two traces of a differential pair have the same length. A mismatch of 5 mm or less is not critical.
- Ensure that the lengths of all pairs don't differ more than 20 mm.
- Place a 100 ohm termination resistor across the traces of each pair as close to the receiver's pins as possible.
- Avoid vias. Run the traces from the connector to the receiver on a single PCB layer if possible.
- Avoid stubs. Run the traces through the termination resistor's solder pads rather than branching the trace. Even small stubs can cause reflections.
Flexible Flat Cable (FFC)#
- Choose an FFC with a differential impedance of 100 ohms to avoid problems with electromagnetic interference (EMI).
- Keep the cable away from unshielded electric motors, transformers, and unshielded coils.
- If you use an FFC without a ground layer, keep the cable away from materials with a high dielectric loss.
- If you use an FFC with a ground layer, make sure to insert the cable with the ground tab facing down.
- When ordering a custom flexible flat cable, specify the FFC connector (see below) to ensure that the ground tab is in the correct position and the retaining tabs have the correct shape.
- When using a standard flexible flat cable without a ground layer and retaining tabs, keep the cable short and avoid proximity to other materials. Note that the pull-out force is reduced when using a cable without retaining tabs.
- Basler recommends using the same connectors on the camera and the system side, although other connectors with the same number of pins can be used.
- The order code of the FFC connector on camera side is Hirose FH41-28S-0.5SH(05). This connector is optimized for impedance controlled flexible flat cables.
- Make sure that the FFC contact pads meet the mechanical specification of the Hirose FH41 connector to avoid shorting the GND layer and the data lines. For more information, see the FH41 Series connector website.
Trigger and General Purpose Input (CC0)#
The LVDS input line can be used to send a trigger signal to the camera. Although the trigger frequency is very moderate, make sure to observe the LVDS design rules to avoid noise being picked up. Noise can cause false trigger events.
In addition, the LVDS input can be used as a general purpose input. The state of the input can be read via the camera's control interface at any time.
The input does not need a termination resistor. The line is terminated at camera side.
In other respects, the same recommendations as for the data output lines apply.
I²C Configuration Interface (I2C_SDA, I2C_SCL, I2C_ID)#
Basler dart BCON for LVDS cameras use the I²C interface to exchange configuration data with the controlling processor.
I²C is an open-collector bus interface with two signal lines, SDA and SCL. Connect these signal lines to the appropriate ports of an I²C controller. Typically, an I²C controller is part of the microcontroller or the System on a Chip (SoC) that you will be using to process the image data.
For more information about I²C, see the I²C-Bus Specification and User Manual.
NOTICE - Voltage outside of the specified range can cause damage.
You must supply camera power that complies with the individual voltage requirements of the BCON for LVDS interface lines:
The nominal voltage for the power supply line (VCC) is 5 VDC.
The nominal voltage for the I²C interface lines (I2C_SCL, I2C_SDA, I2C_ID) is 3.3 VDC.
Design Recommendations for the I²C Interface#
- The voltage level for the I²C bus is 3.3 V. Make sure that the pull-up resistor is connected to 3.3 V.
- If you have only one or two cameras, tie the I2C_ID pin to GND on the first camera and to 3.3 VDC on the second camera. This helps you to identify which camera is connected to a given data interface.
- The capacitive bus load for a single I²C bus segment is limited to 400 pF. Take into account that long flexible flat cables can significantly contribute to the total bus load. If necessary, use more than one I²C bus or use an I²C bus repeater.
- Choose a suitable pull-up resistor. The optimal value depends on the capacitive load of the I²C bus lines. For determining appropriate resistor values, refer to the I²C-Bus Specification and User Manual.
Power Supply (GND, VCC)#
The camera needs a single 5 VDC power supply. Bad power quality can deteriorate the camera's image quality. However, a properly designed switched-mode power supply, as used to supply a USB port, will yield a good result.
Design Recommendations for the Power Supply#
- The power supply should be able to supply 1.5 W per camera. Long cables can cause a significant voltage drop, leading to a higher power consumption than the camera alone.
- Ground noise can cause bad image quality. Make sure that the power supply input on the PCB (VCC and GND) is close to the camera connectors. The processor and the memory should not be placed between the power supply input and the camera connector.
- Provide an extra capacitor directly on the camera connector where the supply voltage is delivered to the camera (e.g. 10 μF MLCC - multi-layer ceramic capacitor). If the supply is noisy, a low-pass-filter consisting of a capacitor and an inductor can help to smoothen the supply voltage.
The BCON for LVDS interface is designed to work with FPGAs as well as Channel Link deserializer devices.
For full speed operation, the FPGA must support a bit rate of at least 560 Mbit/s. The Channel Link deserializer device must support 28 bits and 84 MHz or more.
For a list of suitable Channel Link devices, see the Channel Link Design Guide.