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同轴连接器频率为几百兆赫
发布时间：2017-11-16 9:21:02 来源: 浏览次数：
摘要：同轴连接器当今，电子系统的时钟频率为几百兆赫，所用脉冲的前后沿在亚纳秒范围，高质量视频电路也用以亚纳秒级的象素速率。
上一篇我们送上的文章是现在的光纤连接器的端子图为了更加全面的介绍射频同轴连接器、同轴连接器、光纤连接器各项性能、规格、参数等等，我们将持续发布最新知识，帮助大家了解更多的信息。
同轴连接器当今，电子系统的时钟频率为几百兆赫，所用脉冲的前后沿在亚纳秒范围，高质量视频电路也用以亚纳秒级的象素速率。这些较高的处理速度表示了工程上受到不断的挑战。那么如何预防和解决连接器电磁干扰的问题值得我们关注。电路上振荡速率变得更快(上升/下降时间)，电压/电流幅度变得更大，问题变得更多。因此，今天同以前相比，解决电磁兼容性(EMC)就更艰难了。
The clock frequency coaxial connectors, electronic systems for hundreds of megahertz, the pulse before and after the edge in the subnanosecond range, high quality video circuit is also used to pixel rate sub nanosecond. These higher processing speeds represent an ongoing challenge in engineering. So how to prevent and solve the problem of electromagnetic interference of connectors is worth our attention.
On the circuit, the oscillation rate becomes faster (rise / fall time), the voltage / current amplitude becomes larger, and the problem becomes more. Therefore, it is even harder to solve electromagnetic compatibility
(EMC) today than before.
同轴连接器在电路的两个波节之前，快速变化的脉冲电流，表示了所谓差模噪声源，电路周围的电磁场可以耦合到其它元件上和侵入连接部分。经感性或容性耦合的噪声是共模干扰。射频干扰电流是彼此相同的，系统可以建模为：由噪声源、“受害电路”或“接受者”和回路(通常是底板)组成。用几个因素来描述干扰的大小：噪声源的强度、干扰电流环绕面积的大小、变化速率。于是，尽管在电路中有很可能产生不希望的干扰，噪声几乎总是共模型的。一旦在输入/输出(I/O)连接器和机壳或地平面之间接入电缆，有某些RF电压出现时，导致几毫安的RF电流就能足以超过允许的发射电平。
The coaxial connector changes rapidly the pulse current before the two wave nodes of the circuit, which represents the so-called differential mode noise source. The electromagnetic field around the circuit can be coupled to other components and penetrated into the connecting part. Noise induced by inductive or capacitive coupling is common mode interference. The RF interference currents are identical to each other, and the system can be modeled as a noise source, a victim circuit, a receiver, and a loop (usually a backplane). Several factors are used to describe the magnitude of interference: the intensity of the noise source, the size of the interference current, the area of the noise, and the rate of change.
As a result, the noise is almost always co modeled, although there is likely to be an unexpected interference in the circuit. Once the cable is connected between the input / output (I/O) connector and the chassis or ground plane, some RF voltages are present, resulting in a few Ma of RF current sufficient to exceed the allowable emission level.
噪声的耦合和传播同轴连接器的共模噪声是由于不合理的设计产生的。有些典型的原因是不同线对中个别导线的长度不同，或到电源平面或机壳的距离不同。另一个原因是元件的缺陷，如磁感应线圈与变压器，电容器与有源器件(例如应用特殊的集成电路(ASIC))。
磁性元件，特别是所谓“铁芯扼流圈”型贮能电感器，是用在电源变换器之中的，总是产生电磁场。磁路中的气隙相当于串联电路中的一个大电阻，那儿要消耗较多的电能。
于是，铁芯扼流圈，绕制在铁氧体棒上，在棒周围产生强的电磁场，在电极附近有 强的场强。在使用回描结构的开关电源中，变压器上必定有一个空隙， 其间有很强的磁场。在其中保持磁场 合适的元件是螺旋管，使电磁场沿管芯长度方向分布。这就是在高频工作的磁性元件优选螺旋结构的原因之一。
Noise coupling and propagation of common mode noise in coaxial connectors are due to unreasonable design. Some of the typical reasons are different lengths of individual wires in different lines, or different distances from the power plane or the chassis. Another reason is component defects, such as magnetic induction coils and transformers, capacitors and active devices (such as the use of special integrated circuits (ASIC)).Magnetic components, especially the so-called "iron core choke" type energy storage inductors, are used in power converters, and always generate electromagnetic fields. The air gap in the magnetic circuit is equivalent to a large resistor in the series circuit, where more power is consumed.
Thus, the iron core chokes around the ferrite rod, producing a strong electromagnetic field around the rod, and having the strongest field strength near the electrode. In the switching power supply with flyback structure, there must be a gap on the transformer, and there is a strong magnetic field in it. The most suitable element to maintain the magnetic field is the spiral tube, which makes the electromagnetic field distribute along the length of the tube core. This is one of the reasons why helical components are optimized at high frequencies.
同轴连接器在不恰当的去耦电路通常也变成干扰源。如果电路要求大的脉冲电流，以及局部去耦时不能保证小电容或十分高的内阻需要，则由电源回路产生的电压就下降。这相当于纹波，或者相当于终端间的电压快速变化。由于封装的杂散电容，干扰能耦合到其它电路中去，引起共模问题。
当共模电流污染I/O接口电路时，该问题必须解决在通过连接器之前。不同的应用，建议用不同的方法来解决这个问题。在视频电路中，那儿I/O信号是单端的，且公用同一共同回路，要解决它，用小型LC滤波器滤掉噪声。
在低频串联接口网络中，有些杂散电容就足够将噪声分流到底板上。差分驱动的接口，如以太，通常是通过变压器耦合到I/O区域，是在变压器一侧或两侧的中心抽头提供耦合的。这些中心抽头经高压电容器与底板相连，将共模噪声分流到底板上，以使信号不发生失真。在I/O区域内的共模噪声没有一个通用办法来解决所有类型的I/O接口的问题。设计师们的主要目标是将电路设计好，而常常忽略了一些视为简单的细节。一些基本法则能使噪声在到达连接器以前，降至 小：
1)将去耦电容设置在紧挨负载处。
2)快速变化的前后沿的脉冲电流，其环路尺寸应 小。
3)使大电流器件(即驱动器和ASIC)远离I/O端口。
4)测定信号的完整性，以保证过冲和下冲 小，特别是对于大电流的关键性信号(如时钟，总线)。
5)使用局部滤波，如RF铁氧体，可吸收RF干扰。
6)提供低阻抗搭接到底板上或在I/O区域的基准在底板上。
即使工程师采取许多上述所列的预防措施，来减小在I/O区内的RF噪声，还不能保证这些预防措施能否成功地足够满足发射要求。有些噪声是传导干扰，即在内部电路板上按共模电流流动。这个干扰源是在底板和电路等之间。于是，这个RF电流一定通过 低阻抗(在底板和载信号线之间)的通路流动。如果连接器没呈现足够低的阻抗(与底板的搭接处)，这RF电流经杂散电容流动。当这RF电流流过电缆时，不可避免地产生发射。
Coaxial connectors in inappropriate decoupling circuits are often turned into interference sources. If the circuit requires large pulse current, and the local decoupling can not guarantee small capacitance or very high internal resistance, the voltage generated by the power circuit will drop. This is equivalent to the ripple, or equivalent to the rapid change in voltage between terminals. Due to the stray capacitance of the package, the interference can be coupled to other circuits, causing the common mode problem.
When the common mode current pollutes the I/O interface circuit, the problem must be solved before passing through the connector. Different applications suggest different methods to solve this problem. In the video circuit, where the I/O signal is single ended and shared the same common circuit, to solve it, the noise is filtered out with a small LC filter.
In the low frequency series interface network, some stray capacitances are enough to shunt the noise to the board. A differential drive interface, such as an Ethernet, is usually coupled to the I/O region by a transformer, which provides coupling between the central taps on one side or on both sides of the transformer. The center taps are connected to the backplane by the high voltage capacitor and split the common mode noise to the board so that the signal does not distort.
Common mode noise in the I/O region
There is no common solution to all types of I/O interfaces. The main goal of designers is to design the circuit well, and often ignore some of the simple details. Some basic rules allow noise to be minimized before reaching the connector:
1) set the decoupling capacitor at close to the load.
2) the pulse current of the fast changing front and back sides should be the smallest.
3) make large current devices (drivers and ASIC) away from the I/O port.
4) integrity measurement signal, to ensure minimum overshoot and undershoot, especially for the key signal current (such as clock, bus).
5) using local filtering, such as RF ferrite, can absorb RF interference.
6) provide low impedance lapping on the plate or in the I/O region on the base plate.
Even if engineers take many of these precautions, to reduce the RF noise in the I/O area, it is not possible to ensure that these preventive measures can successfully meet the launch requirements. Some noise is conducted interference, that is, the common mode current flows on the internal circuit board. The source of interference is between the backplane and the circuit.
Thus, this RF current must flow through the lowest impedance (between the backplane and the carrier line). If the connector does not present enough low impedance (with the lap of the base plate), the RF current flows through stray capacitance. When the RF current flows through the cable, it is inevitable to emit.
射频同轴连接器是安装于电缆或仪器在下一篇继续做详细介绍，如需了解更多，请持续关注。
本文由同轴连接器频率为几百兆赫生产厂家亚洲一区二区三区网站于2017-11-16 9:21:02整理发布。
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