同軸連接器頻率為幾百兆赫

發(fā)布時(shí)間：2017-11-16 9:21:02 來源: 瀏覽次數(shù)：

摘要：同軸連接器當(dāng)今，電子系統(tǒng)的時(shí)鐘頻率為幾百兆赫，所用脈沖的前后沿在亞納秒范圍，高質(zhì)量視頻電路也用以亞納秒級(jí)的象素速率。

上一篇我們送上的文章是現(xiàn)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(xiàng)性能、規(guī)格、參數(shù)等等，我們將持續(xù)發(fā)布最新知識(shí)，幫助大家了解更多的信息。

同軸連接器當(dāng)今，電子系統(tǒng)的時(shí)鐘頻率為幾百兆赫，所用脈沖的前后沿在亞納秒范圍，高質(zhì)量視頻電路也用以亞納秒級(jí)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(zhàn)。那么如何預(yù)防和解決連接器電磁干擾的問題值得我們關(guān)注。電路上振蕩速率變得更快(上升/下降時(shí)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(gè)波節(jié)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(jīng)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(tǒng)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(gè)因素來描述干擾的大�。涸肼曉吹膹�(qiáng)度、干擾電流環(huán)繞面積的大小、變化速率。于是，盡管在電路中有很可能產(chǎn)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(jī)殼或地平面之間接入電纜，有某些RF電壓出現(xiàn)時(shí)，導(dǎo)致幾毫安的RF電流就能足以超過允許的發(fā)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(shè)計(jì)產(chǎn)生的。有些典型的原因是不同線對中個(gè)別導(dǎo)線的長度不同，或到電源平面或機(jī)殼的距離不同。另一個(gè)原因是元件的缺陷，如磁感應(yīng)線圈與變壓器，電容器與有源器件(例如應(yīng)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(chǎn)生電磁場。磁路中的氣隙相當(dāng)于串聯(lián)電路中的一個(gè)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(chǎn)生強(qiáng)的電磁場，在電極附近有強(qiáng)的場強(qiáng)。在使用回描結(jié)構(gòu)的開關(guān)電源中，變壓器上必定有一個(gè)空隙，其間有很強(qiáng)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(yōu)選螺旋結(jié)構(gòu)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(dāng)?shù)娜ヱ铍娐吠ǔＲ沧兂筛蓴_源。如果電路要求大的脈沖電流，以及局部去耦時(shí)不能保證小電容或十分高的內(nèi)阻需要，則由電源回路產(chǎn)生的電壓就下降。這相當(dāng)于紋波，或者相當(dāng)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(dāng)共模電流污染I/O接口電路時(shí)，該問題必須解決在通過連接器之前。不同的應(yīng)用，建議用不同的方法來解決這個(gè)問題。在視頻電路中，那兒I/O信號(hào)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(lián)接口網(wǎng)絡(luò)中，有些雜散電容就足夠?qū)⒃肼暦至鞯降装迳�。差分�?qū)動(dòng)的接口，如以太，通常是通過變壓器耦合到I/O區(qū)域，是在變壓器一側(cè)或兩側(cè)的中心抽頭提供耦合的。這些中心抽頭經(jīng)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(hào)不發(fā)生失真。在I/O區(qū)域內(nèi)的共模噪聲沒有一個(gè)通用辦法來解決所有類型的I/O接口的問題。設(shè)計(jì)師們的主要目標(biāo)是將電路設(shè)計(jì)好，而常常忽略了一些視為簡單的細(xì)節(jié)。一些基本法則能使噪聲在到達(dá)連接器以前，降至 �。�

1)將去耦電容設(shè)置在緊挨負(fù)載處。

2)快速變化的前后沿的脈沖電流，其環(huán)路尺寸應(yīng) 小。

3)使大電流器件(即驅(qū)動(dòng)器和ASIC)遠(yuǎn)離I/O端口。

4)測定信號(hào)的完整性，以保證過沖和下沖小，特別是對于大電流的關(guān)鍵性信號(hào)(如時(shí)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(qū)域的基準(zhǔn)在底板上。

即使工程師采取許多上述所列的預(yù)防措施，來減小在I/O區(qū)內(nèi)的RF噪聲，還不能保證這些預(yù)防措施能否成功地足夠滿足發(fā)射要求。有些噪聲是傳導(dǎo)干擾，即在內(nèi)部電路板上按共模電流流動(dòng)。這個(gè)干擾源是在底板和電路等之間。于是，這個(gè)RF電流一定通過低阻抗(在底板和載信號(hào)線之間)的通路流動(dòng)。如果連接器沒呈現(xiàn)足夠低的阻抗(與底板的搭接處)，這RF電流經(jīng)雜散電容流動(dòng)。當(dāng)這RF電流流過電纜時(shí)，不可避免地產(chǎn)生發(fā)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(xù)做詳細(xì)介紹，如需了解更多，請持續(xù)關(guān)注。
本文由同軸連接器頻率為幾百兆赫生產(chǎn)廠家鎮(zhèn)江市丹徒區(qū)乾升光電設(shè)備有限公司于2017-11-16 9:21:02整理發(fā)布。
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