同軸連接器頻率為幾百兆赫

發布時間：2017-11-16 9:21:02 來源: 瀏覽次數：

摘要：同軸連接器當今，電子系統的時鐘頻率為幾百兆赫，所用脈沖的前后沿在亞納秒范圍，高質量視頻電路也用以亞納秒級的象素速率。

上一篇我們送上的文章是現在的光纖連接器的端子圖為了更加全面的介紹射頻同軸連接器、同軸連接器、光纖連接器各項性能、規格、參數等等，我們將持續發布最新知識，幫助大家了解更多的信息。

同軸連接器當今，電子系統的時鐘頻率為幾百兆赫，所用脈沖的前后沿在亞納秒范圍，高質量視頻電路也用以亞納秒級的象素速率。這些較高的處理速度表示了工程上受到不斷的挑戰。那么如何預防和解決連接器電磁干擾的問題值得我們關注。電路上振蕩速率變得更快(上升/下降時間)，電壓/電流幅度變得更大，問題變得更多。因此，今天同以前相比，解決電磁兼容性(EMC)就更艱難了。

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.

同軸連接器在電路的兩個波節之前，快速變化的脈沖電流，表示了所謂差模噪聲源，電路周圍的電磁場可以耦合到其它元件上和侵入連接部分。經感性或容性耦合的噪聲是共模干擾。射頻干擾電流是彼此相同的，系統可以建模為：由噪聲源、“受害電路”或“接受者”和回路(通常是底板)組成。用幾個因素來描述干擾的大小：噪聲源的強度、干擾電流環繞面積的大小、變化速率。于是，盡管在電路中有很可能產生不希望的干擾，噪聲幾乎總是共模型的。一旦在輸入/輸出(I/O)連接器和機殼或地平面之間接入電纜，有某些RF電壓出現時，導致幾毫安的RF電流就能足以超過允許的發射電平。

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.

噪聲的耦合和傳播同軸連接器的共模噪聲是由于不合理的設計產生的。有些典型的原因是不同線對中個別導線的長度不同，或到電源平面或機殼的距離不同。另一個原因是元件的缺陷，如磁感應線圈與變壓器，電容器與有源器件(例如應用特殊的集成電路(ASIC))。

磁性元件，特別是所謂“鐵芯扼流圈”型貯能電感器，是用在電源變換器之中的，總是產生電磁場。磁路中的氣隙相當于串聯電路中的一個大電阻，那兒要消耗較多的電能。

于是，鐵芯扼流圈，繞制在鐵氧體棒上，在棒周圍產生強的電磁場，在電極附近有強的場強。在使用回描結構的開關電源中，變壓器上必定有一個空隙，其間有很強的磁場。在其中保持磁場合適的元件是螺旋管，使電磁場沿管芯長度方向分布。這就是在高頻工作的磁性元件優選螺旋結構的原因之一。

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.

同軸連接器在不恰當的去耦電路通常也變成干擾源。如果電路要求大的脈沖電流，以及局部去耦時不能保證小電容或十分高的內阻需要，則由電源回路產生的電壓就下降。這相當于紋波，或者相當于終端間的電壓快速變化。由于封裝的雜散電容，干擾能耦合到其它電路中去，引起共模問題。

當共模電流污染I/O接口電路時，該問題必須解決在通過連接器之前。不同的應用，建議用不同的方法來解決這個問題。在視頻電路中，那兒I/O信號是單端的，且公用同一共同回路，要解決它，用小型LC濾波器濾掉噪聲。

在低頻串聯接口網絡中，有些雜散電容就足夠將噪聲分流到底板上。差分驅動的接口，如以太，通常是通過變壓器耦合到I/O區域，是在變壓器一側或兩側的中心抽頭提供耦合的。這些中心抽頭經高壓電容器與底板相連，將共模噪聲分流到底板上，以使信號不發生失真。在I/O區域內的共模噪聲沒有一個通用辦法來解決所有類型的I/O接口的問題。設計師們的主要目標是將電路設計好，而常常忽略了一些視為簡單的細節。一些基本法則能使噪聲在到達連接器以前，降至小：

1)將去耦電容設置在緊挨負載處。

2)快速變化的前后沿的脈沖電流，其環路尺寸應小。

3)使大電流器件(即驅動器和ASIC)遠離I/O端口。

4)測定信號的完整性，以保證過沖和下沖小，特別是對于大電流的關鍵性信號(如時鐘，總線)。

5)使用局部濾波，如RF鐵氧體，可吸收RF干擾。

6)提供低阻抗搭接到底板上或在I/O區域的基準在底板上。

即使工程師采取許多上述所列的預防措施，來減小在I/O區內的RF噪聲，還不能保證這些預防措施能否成功地足夠滿足發射要求。有些噪聲是傳導干擾，即在內部電路板上按共模電流流動。這個干擾源是在底板和電路等之間。于是，這個RF電流一定通過低阻抗(在底板和載信號線之間)的通路流動。如果連接器沒呈現足夠低的阻抗(與底板的搭接處)，這RF電流經雜散電容流動。當這RF電流流過電纜時，不可避免地產生發射。

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.

射頻同軸連接器是安裝于電纜或儀器在下一篇繼續做詳細介紹，如需了解更多，請持續關注。
本文由同軸連接器頻率為幾百兆赫生產廠家鎮江市丹徒區乾升光電設備有限公司于2017-11-16 9:21:02整理發布。
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