Keyword: PCB layout design, PCB installed, PCB, PCB layout, PCB design
Now more and more to run one billion - bit rate video equipment, they through relatively large coaxial BNC connector interconnection. Although the BNC connectors are usually have good quality, but they are depends on their performance in the equipment on the PCB installed. Not optimized connector placeholder design can lead to impedance mismatch, reflection, loss of signal, and reduce the fidelity of signal equipment. BNC placeholder PCB layout design task, generally by the circuit wiring designers and hardware engineer is responsible for, but they usually don't have the time or the suitable tools to complete the task smoothly. This paper introduces some common problems in the design of BNC placeholder, and explains the edge with illustrations pasted on and plug-in connector holder design example. These connectors but with national semiconductor LMH0384 3 g/HD/SD adaptive cable equalizer, LMH0303 cable drive and LMH0387 collocation USES configurable I/O device.
The type of the BNC
Video equipment in history have been the BNC and 75? Coaxial cable is tie-in. Video images in the past to sd rate (270 MBPS) transmission, then rose to hd rate (1.485 Gbps), is now into 3 Gbps. BNC connector must be in a loss of signal under the condition of minimum support 3 GBPS of signal transmission, and to maintain 75? Characteristic impedance and reflection to a minimum.
Many connector suppliers according to the PCB, SMT way to provide different types of BNC. Based on the mechanical considerations, these connectors can be used in a vertical edge or SMT SMT, right Angle pasted on. In terms of electrical signal pin or SMT connection welding plate on the top circuit board or welding in metallized hole, signal wiring is located at the other side of the circuit board.
BNC test
BNC is a kind of coaxial connectors, specially designed to support up to 3 GBPS of video transmission, its performance mainly depends on the coaxial structure inside the BNC, transform from the BNC connector to the PCB will seriously affect the performance of the BNC. Well-designed BNC placeholder to maintains the BNC characteristic impedance bandwidth and its essential.
Time domain reflectometry (TDR) is a quick inspection no signal pin or placeholder BNC coaxial structure internal performance of a very good tool. Tested the simple way is to use flat metal BNC with signal pin block pin short circuit, and then spread to the BNC TDR step pulse. By measuring from the launch of TDR step pulse is reflected back to the signal, instrument can measure the impedance during the step pulse transmission.
