首页资源分类PCB layout > pcb设计之旁路技术

pcb设计之旁路技术

已有 445010个资源

下载专区

文档信息举报收藏

标    签:旁路

分    享:

文档简介

讲得不好,大家多指教,望能对大家有帮助

文档预览

 介绍   绕过和分离的话题很少,如果有的话,淹没在教室里,但强调在几乎所有数据表和应用笔记!(Bypassing and decoupling are subjects that are rarely, if ever, covered in the classroom; but are emphasized in nearly ALL Data Sheets & Application Notes !)   的遗产,许多新的工程师和技术员忽略它,但是他们会承担风险,它是原型硬件调试问题的最大原因!(The legacy of this is that many new engineers and some technicians ignore it, but they do so at their peril; it is the single greatest reason for prototype hardware debugging problems!) 绕过是什么?(WHAT IS BYPASSING?) 为任何活跃的设备时,有一个压倒一切的要求:电源的的入口点(电力铁路)是低阻抗(相对于地面),即理想:零欧姆!这将有助于确保稳定的电路:电路的完整性。(When powering any active device, there is one overriding requirement: that the point of entry of the power supply (Power Rail) be as LOW an impedance (relative to ground) as possible, i.e., ideally: zero ohms! This will help to insure the stability of the circuit: Circuit Integrity.) 为什么我们绕过?(WHY DO WE BYPASS?) 绕过的原因是为了防止不必要的不同设备之间的通信(或同一设备的不同阶段)铁路共享相同的权力。隐含在这个需求,减少噪声存在,权力抱怨所有的频率。(The reason for bypassing is to prevent unwanted communications between different devices (or different stages of the same device) that share the same power rail. Also, implicit in this requirement, is the reduction of NOISE present on that power rail–at all frequencies.) 我们如何绕过?(HOW DO WE BYPASS?) 这样简单的电力和地面之间放置了旁路电容器(Vcc和接地)的每个活动装置,将有效地恢复这近理想的力量supply-zero欧姆输出阻抗!(Something as simple as placing a bypass capacitor between power and ground (Vcc and Gnd) of each active device, will effectively restore this nearly ideal power supply–zero ohms output impedance!) 注意如何绕过变得更加有效地指挥方法连续平面。地面飞机通常用于高频电路板出于这个原因。(Note how the Bypassing becomes more effective as the ground conductor approaches a continuous plane.  Ground planes are often used in high frequency circuit boards for this reason.)  权力Rails(Power Rails) 因为有距离任何电源和有源设备力量,有限长度的导线、线、或跟踪,电源和设备之间是必需的。(Because there is distance between any power source and the active device it powers, a conductor, wire, or trace of finite length is required between that power source and device.)   任何导线、导线或跟踪电阻和电感的特性,可能会导致问题,权力而言。阻力问题可以克服通过增加导体的横截面积;然而,归纳属性是另一个故事。(Any conductor, wire, or trace has the properties of resistance and inductance; both can cause problems where power is concerned. The resistance problem can be overcome by increasing the cross-sectional area of the conductor; however, the inductive property is another story.) 甚至可能似乎是一个小电感,在高频率,或非常高的频率,可以转化为不可接受的高阻抗。见下图:(Even what might appear to be a small inductance, at high frequencies, or very high frequencies, can translate to an unacceptable high impedance. See the figure below:) 注意,感抗(XL)的有限长导体这个零欧姆阻抗的影响。因此活跃设备需要不同利率的当前创造了更多的噪音随着导体长度(电抗)的增加。(Notice how the Inductive Reactance (XL) of the finite length conductor effects this Zero Ohms Impedance. Hence the active device’s need for varying rates of current creates more NOISE as the conductor length (and the reactance) increases.)。 添加一个旁路电容器这感抗有助于恢复(虚拟)零欧姆阻抗。(Adding a Bypass Capacitor to this Inductive Reactance helps to restore the (virtual) Zero Ohms Impedance.)。    在这一点上,值得注意的是,所有活动设备输入和outputs-but你已经知道没有你!你可能没有考虑的是,电力铁路Vcc pin能是两个,一个输入和输出端口。“你只需要检查这些设备的原理,电力铁路是常见的输入和输出阶段,即。,输入级的偏置电阻连接到相同的“铁路”随着负载电阻的输出阶段。(At this point, it is worth noting that ALL active devices have inputs and outputs–but you already knew that didn’t you! What you may not have considered is that the power rail–the Vcc pin–can be both, an input and output “port.” You only have to examine the schematic of such devices to see that the power rail is common to both input and output stages, i.e., the bias resistors of the input stage are connected to the same “Rail” as the load resistors of the output stages)。 这样的安排并不是一件坏事,因为它假设,这个共同的力量总是会铁路举行零欧姆!也就是说,它将通过一个理想电压源采购(This arrangement is not a Bad Thing, because it presupposes that this common power rail will always be held at Zero Ohms! That is, it will be sourced by an Ideal Voltage Source)。 放大器与不同程度的电力供应稳定的形式绕过&脱钩(Amplifier with various degrees of Power Supply Stabilization in the form of Bypass & Decoupling) 注意电源rail-Vcc pin能是两个,一个输入和输出端口。(Notice how the power rail–Vcc pin–can be both, an input and output “PORT.”)。   TTL   TTL(晶体管晶体管逻辑)逻辑是一个大的噪音来源。在一个典型的TTL逻辑设备(门、触发器、计数器,登记,等等),这是公平地说,在任何一个时间:晶体管的一半,而另一半。然而,在逻辑转换,很短的时间内所有的晶体管。(In a typical TTL logic device (gate, flip flop, counter, register, etc.), it is fair to say that at any one time: half of the transistors are ON, and the other half are OFF. However, during logic transitions, for a very short time ALL of the transistors are ON)。  TTL是“饱和逻辑”,即。晶体管是完全或完全,当它完全是,Vsat。(TTL is a “Saturating Logic,” i.e., a transistor is either fully off or fully on, and when it is fully on it is said to be, in Vsat)。   饱和晶体管需要更多的时间来变得比它走上成为饱和不饱和的;这种时差称为存储时间(Ts)。(A saturated transistor requires more time to become unsaturated than it took to become saturated in the first place; this time difference is called storage time (Ts))。 因此,任何逻辑过渡期间(一个零或零/一个)的所有晶体管在这么短的时间内(Ts)画~正常电流的两倍。这种延迟可以持续两个或三个纳秒到只要十五nanoseconds-depending逻辑家庭。(Therefore, during any logic transition (one/zero or zero/one) All of the transistors are ON for this short time (Ts)–drawing ~twice its normal current. This latency can last from two or three nanoseconds to as long as fifteen nanoseconds–depending on the logic family)。 见下图: (See the figure below): 在系统使用数千人,成千上万的盖茨,可能有一个巨大的供电需求,即。,提供一个常数,non-varying Vcc的负荷是随机的和非常高的速度(快di-dt,即。,一个大电流变化在短时间内)。(In systems using thousands, to hundreds of thousands of gates, there can be a tremendous demand on the power supply, i.e., supplying a constant, non-varying Vcc to a load that is random and very high speed (fast di-dt, i.e., a large current change in a short period of time).) 如果能供电的所有逻辑设备以恒定Vcc,一切都会出色的热心。不过,墨菲生活,不允许任何处理工程设计、出色的。游手好闲的人!(If one could supply power to all of the logic devices at a constant Vcc, everything would be Peachy Keen. However, Life–and Murphy, do not allow anything dealing with engineering design, to be Peachy. –Bummer!) 正如前面所提到的:(As mentioned previously:) 因为没有任何电源之间的“距离”的逻辑力量,有限长度的导线、线、或跟踪这个电源和逻辑之间的需要。(Because there is “Distance” between any power source and the logic it powers, a conductor, wire, or trace of finite length is required between this power source and the logic.)    任何导线、导线或跟踪电阻和电感的特性,可能会导致问题,权力而言。可以克服阻力的问题增加横截面积,然而,归纳属性是另一个故事。(Any conductor, wire, or trace have the properties of resistance and Inductance; both can cause problems where power is concerned. The resistance problem can be overcome by increasing the cross-sectional area, however, the Inductive property is another story.)   甚至可能似乎是一个小电感,在高频率,或非常高的频率,可以转化为不可接受的高阻抗。(Even what might appear to be a small inductance, at high frequencies, or very high frequencies, can translate to an unacceptable high impedance。) 在放大器的情况下,以上,TTL逻辑器件输入和输出,以及铁路Vcc pin能是两个,一个输入和输出端口。”同样,电路的检查表明,电力铁路是常见的输入和输出阶段,即。,输入级的偏置电阻连接到相同的“铁路”随着负载电阻的输出阶段。(As in the case of the amplifier, above, TTL logic devices have inputs and outputs; and the power rail–the Vcc pin–can be both, an input and output “port.” Again, an examination of the circuit reveals that the power rail is common to both input and output stages, i.e., the bias resistors of the input stage are connected to the same “Rail” as the load resistors of the output stages.) 这样的安排,前提,这个共同的力量总是会铁路举行零欧姆!也就是说,它将通过一个理想电压源采购。(This arrangement, again, presupposes that this common power rail will always be held at Zero Ohms! That is, it will be sourced by an Ideal Voltage Source.) 回顾(RECAP) 世界的快速边缘敏感的逻辑,这是一个简单的构思逻辑器件之间的“不适当的通讯”(&元素在一个设备)通过无保护,高阻抗rail-Vcc力量。(In the world of fast edge sensitive logic, it is a simple matter to conceive of “inappropriate communications” between logic devices (& elements within a device) through the unprotected, high impedance power rail–Vcc.) 由于这种需求的速度在权力supply-Rise和下降时间nanoseconds-the数百兆赫兹的频率。任何导体,印刷电路跟踪、或线,设备之间的任何导体,权力销和电源可以看起来像一个高得令人无法接受resistance-tens几百欧姆欧姆。(Because of the speed of this demand on the power supply–Rise and Fall times in the nanoseconds–the frequencies are in the many hundreds of MHz. And, any conductor, be it printed circuit trace, or wire, any conductor, between the device power pin and the power source can look like an unacceptably high resistance–tens of Ohms to hundreds of Ohms.) 这样简单的放置电容Vcc和地面之间的每个逻辑设备,将有效地创建这接近理想的力量supply-Zero欧姆输出阻抗!(Something as simple as placing a capacitor between Vcc and ground of each logic device, will effectively create this near Ideal power supply–Zero Ohms output impedance!)       

Top_arrow
回到顶部
EEWORLD下载中心所有资源均来自网友分享,如有侵权,请发送举报邮件到客服邮箱bbs_service@eeworld.com.cn 或通过站内短信息或QQ:273568022联系管理员 高员外,我们会尽快处理。