tag 标签: rf

  • 热度 14
    2015-7-10 21:19
    1276 次阅读|
    0 个评论
    Typically, microwave ovens are known for being useful for warming things up rather than cooking food. In fact, even the traditional TV dinner either ends up with a cold centre or overcooked at the edges. Now imagine a microwave oven that can cook a whole meal heating the different parts at different rates and intensities so that vegetables, meat and pasta and rice are cooked exactly right — but leaving the ice-cream ice cold!   Not only that, such an oven could be connected to the Internet or IoT, or read a smart RFID tag on a prepared dinner and know exactly how to cook the meal in a minimal amount of time. Freescale Semiconductor recently introduced its vision for a radically innovative appliance concept that leverages solid-state radio frequency technology to revolutionize cooking. Developed in partnership with global product strategy and design firm frog, this breakthrough proof of concept will help enable fresh, chef-quality meals available at home with virtually no effort or prep time. With the convenience of a microwave and quality of a traditional oven, this smart, connected RF cooking concept can control where, when and how much heating energy is directed into food – enabling more precise cooking for dramatically improved consistency, taste and nutrition. This fine-tuned heating capability helps prevent overcooking, which can destroy nutritional content, reduce moisture and waste energy. Solid state RF cooking technology can also enable appliance OEMs to create products capable of cooking multiple dishes and items at the same time within the same appliance, significantly simplifying meal preparation. By precisely controlling the location, cycles, and levels of cooking energy, the appliance will bring food from a raw or frozen state to a cooked temperature rapidly and without intervention. With the addition of convection heating to enable browning and crisping, the oven concept can also support a wide array of cooking types and qualities, from searing to browning to baking to poaching. “Consumers worldwide are strapped for time but still want nutrient-rich, high quality meals at home,” said Paul Hart, senior vice president and general manager for Freescale’s RF business. “They will no longer need to choose between quality and convenience. Imagine not only having ready-to cook, gourmet meals delivered to your door, but achieving restaurant-quality results in mere minutes.”   With the emerging IoT, the era of the smart homes and smart cooking is beginning to take shape. This breakthrough paves the way for a host of new business models and opportunities, including internet-driven home delivery of freshly prepared meals from a variety of sources — including restaurants, grocery stores and farm-to-table cooperatives — all quickly and easily cooked in the appliance. The concept also holds the broader potential of improving food supply chain efficiency by collecting and transmitting Big Data sets which can contribute to more efficient food distribution, targeted services and enhanced products.   Jean-Pierre Joosting  
  • 热度 12
    2014-7-4 17:39
    1841 次阅读|
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    At one of the Gadget Smackdown sessions at the EE Live! 2014 conference and exhibition, I introduced a conceptual project that I hope to make reality soon. This project is an open-source radio transmitter for RC hobbyists. This transmitter will be reconfigurable, allowing it to operate over multiple frequency bands using multiple protocols. The plan is to create a modular, open-source, software-defined radio (SDF), but what brought about the need for something like this? Typical hobbyist RC transmitter.   With the advent of WiFi and other chips operating in the 2.4 GHz band, there has been significant development in the miniaturization and integration of RFICs. Due to the integrated nature of these chips, and the many features they offer, the RC industry has moved from the traditional 72 MHz and 75 MHz bands to 2.4 GHz. This transition has been anything but clean. The old frequency bands operated under an (relatively) industry-standard protocol. This was a simple analog frequency-shift keying (FSK) protocol -- effectively pulse-width modulation imposed on an FSK signal. There were only two variations of this protocol, but both were well known and well- documented.   When the industry started its shift to 2.4 GHz, all the vendors used their own proprietary protocols. This means that transmitters and receivers from different vendors are incompatible with one another. This was not the first time the industry had tried this, and it quickly became apparent that the various vendors were up to the same old tricks. As the switch to 2.4 GHz continued, the number of proprietary protocols kept growing; there are now at least 10. The switch also reduced the number of vendors offering hardware in the old transmission bands. For those (like myself) operating RC submarines, this has been very detrimental, since 2.4 GHz signals don't penetrate the water.   What is one to do? This is where my solution comes into play. There have been great advancements in software-defined radios, which can transmit across multiple bands and be reconfigured to support multiple protocols. Lime Microsystems has a new RFIC that can transmit from 50 MHz all the way up to 3.8 GHz. This would allow for coverage of legacy bands as well as the new 2.4 GHz band. Since it is a software-defined radio, one could also configure the device for each proprietary protocol. As manufacturers develop new protocols, once they are reverse engineered, they could be uploaded to the transmitter. Then all the user would need to do is select the desired protocol at startup.   With the RF section conceptualized, the rest of the device would consist of a reconfigurable board that would allow the user to implement 1-20 channels. Each connection could be a simple on-off switch, an analog potentiometer for a standard set of gimbals found in current transmitters, or serial protocol devices. Devices using serial communications might include such things as motion and position sensors, magnetometers, or pressure transducers. Once connected to the inputs of the core, they would be configured either via a desktop application or on the screen of the transmitter itself. With the RF section, interface connections, and screen, this would form the core of a handheld transmitter.   The beauty of this approach to designing a RC handheld transmitter is that it allows users to create and customize their transmitters as required. Custom enclosure designs can be created and shared. If one needs to add another channel, this will be as easy as attaching the user input device to the core and configuring it. This transmitter customization approach will add a new element to the hobby. This element would be consistent with both the Maker/Hacker movements.   Personally, I want to design an enclosure similar to a device found from the TV series Leverage . In the " First Contact Job " in the fifth season, Harrison had a handheld device that he called the Marvin. This had a very unique shape that I think would lend itself to support the features I need for my RC submarines.   The Marvin, Leverage (Season 5, Episode 3, "The First Contact Job").   To pull this RC transmitter concept off, I will need to learn a lot. I have yet to really play with designing any sort of graphical interface on a microcontroller. I do not see this as a major hurdle, but it will require some learning. I will also need to learn a bit about general RF design and the nuances of ultra-high-frequency PCB design. Is this a lot to learn? Well, yes, but I find that having a project is the best way to start learning. If you happen to have any ideas, or if you would like to contribute your efforts to a project like this, please let me know in the comments below.   Adam Carlson is Senior Mechanical Design Engineer at Eagle Technologies .
  • 热度 19
    2013-10-2 15:57
    1008 次阅读|
    0 个评论
    Early in my career, I held an engineering technician post in the RD department of a company that designed and manufactured active signal processing components in RF and microwave technologies. An engineer at the company had been assigned a project to come up with a design for an RF two-power power splitter with an insertion loss from 100MHz to 1GHz of ± 0.25 db across the entire frequency span. The physical design of a splitter is fairly simple: It consists of two miniature toroids, wire, one capacitor, and a gold-plated flat pack. Well, one morning, the design engineer had me wrap the toroids with No. 36 AWG wire, forming an auto-transformer on one-half of the toroid, and a simple balanced coil with a midpoint tap forming two equally wound halves to create a splitter with two output ports, each having an impedance of 50Ω. The tap of the coil would be attached to the tap of the auto-transformer, and the capacitor connected at the junction of the taps to match the input port to the two output ports for minimal insertion loss. After I had wound the two toroids, I mounted them and the capacitor into a metal flat pack (to be hermetically sealed). We took the device over to the test bench to run the device through its test parameters, measuring the standing wave ratio, input to output ports insertion loss. We readily noticed that the insertion loss was measuring about ±0.5-1.5 db. We were looking for an insertion loss of ± 0.25 db across the entire frequency range. For a couple of days, the design engineer went back and forth between calculations and testing. He finally gave up, claiming that the insertion loss requirement was not doable. As the design engineer, understandably frustrated and angry, got up from the test bench, I asked him if I could try something. At that point, he really didn't care, so he let me take a shot at the design. Now, this is where the analyser comes in. I had noticed that the insertion loss from input port to either output port was cutting off short like a low-pass filter. This told me that toroids were not wound with the right wire gauge, and that the auto-transformer toroid needed more twists per inch and a change in wire gauge to achieve a different characteristic impedance. I went to my workbench and began winding some new toroids with No. 37 AWG THN wire with about 10 twists per inch. The number of turns for the auto-transformer and the output coil remained the same, and I kept the same value of capacitance that would balance (match) the input impedance to the two outputs of 50Ω each. This meant that an impedance of 100Ω was needed at the junction of the two taps and capacitor in order to have a balanced split. When I was finished winding the toroids and mounting them, and the capacitor into another gold-plated flat pick, I took the device over to the test bench and ran the test parameters. Insertion loss was ± 0.25 db flat across the entire frequency span. At first, I couldn't believe I hit it on the first try, so I made certain my frequency generator was set correctly, and that the RF analyser was properly zeroed out to account for any loss introduced by the test setup and test fixture. Once I was certain my setup and measurements were correct and repeatable, I called the design engineer back over to the test bench and showed him how this design met the customer's specifications. He then took over the testing himself and came up with the same measurements. We made sure the design was stable by building a few more of these two-port power splitters using the design I came up with. The design was repeatable. He then had me take these packages, hermetically seal them, and run them through ambient air, elevated heat, and cold according to DOD specifications. The design was solid, and the insertion loss and standing wave ratio remained within specifications. There you have it—a design that was abandoned and brought back to life in a spectacular way. Why is this situation memorable? This story is quick and simple, but it gave me confidence by demonstrating my ability to interpret analysers. And it was my first job in an RD department, and I was looking to make an impression. This article was submitted by Bennie Walton, a design engineer, as part of Frankenstein's Fix, a design contest hosted by EE Times (US).
  • 热度 23
    2013-5-6 09:44
    1146 次阅读|
    12 个评论
  • 热度 12
    2010-5-25 09:16
    1476 次阅读|
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             好久没弄Blog了,不过居然申请到了总不能空着吧。就随便说些简单点的又通用的小技巧吧。        新一轮蓝牙设备、无绳电话和蜂窝电话需求高潮正促使中国电子工程师越来越关注 RF 电路设计技巧。 RF 电路板的设计是最令设计工程师感到头疼的部分,如想一次获得成功,仔细规划和注重细节是必须加以高度重视的两大关键设计规则。        今天的蜂窝电话设计以各种方式将所有的东西集成在一起,这对 RF 电路板设计来说很不利。现在业界竞争非常激烈,人人都在找办法用最小的尺寸和最小的成本集成最多的功能。模拟、数字和 RF 电路都紧密地挤在一起,用来隔开各自问题区域的空间非常小,而且考虑到成本因素,电路板层数往往又减到最小。令人感到不可思议的是,多用途芯片可将多种功能集成在一个非常小的裸片上,而且连接外界的引脚之间排列得又非常紧密,因此 RF 、 IF 、模拟和数字信号非常靠近,但它们通常在电气上是不相干的。电源分配可能对设计者来说是一个噩梦,为了延长电池寿命,电路的不同部分是根据需要而分时工作的,并由软件来控制转换。这意味着你可能需要为你的蜂窝电话提供 5 到 6 种工作电源。 在设计 RF 布局时,有几个总的原则必须优先加以满足:        尽可能地把高功率 RF 放大器 (HPA) 和低噪音放大器 (LNA) 隔离开来,简单地说,就是让高功率 RF 发射电路远离低功率 RF 接收电路。如果你的 PCB 板上有很多物理空间,那么你可以很容易地做到这一点,但通常元器件很多, PCB 空间较小,因而这通常是不可能的。你可以把他们放在 PCB 板的两面,或者让它们交替工作,而不是同时工作。高功率电路有时还可包括 RF 缓冲器和压控制振荡器 (VCO) 。       确保 PCB 板上高功率区至少有一整块地,最好上面没有过孔,当然,铜皮越多越好。       芯片和电源去耦同样也极为重要。       RF 输出通常需要远离 RF 输入。       敏感的模拟信号应该尽可能远离高速数字信号和 RF 信号。       设计分区可以分解为物理分区和电气分区。物理分区主要涉及元器件布局、朝向和屏蔽等问题;电气分区可以继续分解为电源分配、 RF 走线、敏感电路和信号以及接地等的分区。       首先我们讨论物理分区问题。元器件布局是实现一个优秀 RF 设计的关键,最有效的技术是首先固定位于 RF 路径上的元器件,并调整其朝向以将 RF 路径的长度减到最小,使输入远离输出,并尽可能远地分离高功率电路和低功率电路。       最有效的电路板堆叠方法是将主接地面 ( 主地 ) 安排在表层下的第二层,并尽可能将 RF 线走在表层上。将 RF 路径上的过孔尺寸减到最小不仅可以减少路径电感,而且还可以减少主地上的虚焊点,并可减少 RF 能量泄漏到层叠板内其他区域的机会。       在物理空间上,像多级放大器这样的线性电路通常足以将多个 RF 区之间相互隔离开来,但是双工器、混频器和中频放大器 / 混频器总是有多个 RF/IF 信号相互干扰,因此必须小心地将这一影响减到最小。 RF 与 IF 走线应尽可能走十字交叉,并尽可能在它们之间隔一块地。正确的 RF 路径对整块 PCB 板的性能而言非常重要,这也就是为什么元器件布局通常在蜂窝电话 PCB 板设计中占大部分时间的原因。         在蜂窝电话 PCB 板上,通常可以将低噪音放大器电路放在 PCB 板的某一面,而高功率放大器放在另一面,并最终通过双工器把它们在同一面上连接到 RF 端和基带处理器端的天线上。需要一些技巧来确保直通过孔不会把 RF 能量从板的一面传递到另一面,常用的技术是在两面都使用盲孔。可以通过将直通过孔安排在 PCB 板两面都不受 RF 干扰的区域来将直通过孔的不利影响减到最小。       有时不太可能在多个电路块之间保证足够的隔离,在这种情况下就必须考虑采用金属屏蔽罩将射频能量屏蔽在 RF 区域内,但金属屏蔽罩也存在问题,例如:自身成本和装配成本都很贵;       外形不规则的金属屏蔽罩在制造时很难保证高精度,长方形或正方形金属屏蔽罩又使元器件布局受到一些限制;金属屏蔽罩不利于元器件更换和故障定位;由于金属屏蔽罩必须焊在地上,必须与元器件保持一个适当距离,因此需要占用宝贵的 PCB 板空间。       尽可能保证屏蔽罩的完整非常重要,进入金属屏蔽罩的数字信号线应该尽可能走内层,而且最好走线层的下面一层 PCB 是地层。 RF 信号线可以从金属屏蔽罩底部的小缺口和地缺口处的布线层上走出去,不过缺口处周围要尽可能地多布一些地,不同层上的地可通过多个过孔连在一起。       尽管有以上的问题,但是金属屏蔽罩非常有效,而且常常还是隔离关键电路的唯一解决方案。       此外,恰当和有效的芯片电源去耦也非常重要。许多集成了线性线路的 RF 芯片对电源的噪音非常敏感,通常每个芯片都需要采用高达四个电容和一个隔离电感来确保滤除所有的电源噪音 。        最小电容值通常取决于其自谐振频率和低引脚电感, C4 的值就是据此选择的。 C3 和 C2 的值由于其自身引脚电感的关系而相对较大一些,从而 RF 去耦效果要差一些,不过它们较适合于滤除较低频率的噪声信号。电感 L1 使 RF 信号无法从电源线耦合到芯片中。记住:所有的走线都是一条潜在的既可接收也可发射 RF 信号的天线,另外将感应的射频信号与关键线路隔离开也很必要。        这些去耦元件的物理位置通常也很关键,图 2 表示了一种典型的布局方法。这几个重要元件的布局原则是: C4 要尽可能靠近 IC 引脚并接地, C3 必须最靠近 C4 , C2 必须最靠近 C3 ,而且 IC 引脚与 C4 的连接走线要尽可能短,这几个元件的接地端 ( 尤其是 C4) 通常应当通过下一地层与芯片的接地引脚相连。将元件与地层相连的过孔应该尽可能靠近 PCB 板上元件焊盘,最好是使用打在焊盘上的盲孔以将连接线电感减到最小,电感应该靠近 C1 。         一块集成电路或放大器常常带有一个开漏极输出,因此需要一个上拉电感来提供一个高阻抗 RF 负载和一个低阻抗直流电源,同样的原则也适用于对这一电感端的电源进行去耦。有些芯片需要多个电源才能工作,因此你可能需要两到三套电容和电感来分别对它们进行去耦处理,如果该芯片周围没有足够空间的话,那么可能会遇到一些麻烦。       记住电感极少并行靠在一起,因为这将形成一个空芯变压器并相互感应产生干扰信号,因此它们之间的距离至少要相当于其中一个器件的高度,或者成直角排列以将其互感减到最小。       电气分区原则大体上与物理分区相同,但还包含一些其它因素。现代蜂窝电话的某些部分采用不同工作电压,并借助软件对其进行控制,以延长电池工作寿命。这意味着蜂窝电话需要运行多种电源,而这给隔离带来了更多的问题。电源通常从连接器引入,并立即进行去耦处理以滤除任何来自线路板外部的噪声,然后再经过一组开关或稳压器之后对其进行分配。       蜂窝电话里大多数电路的直流电流都相当小,因此走线宽度通常不是问题,不过,必须为高功率放大器的电源单独走一条尽可能宽的大电流线,以将传输压降减到最低。为了避免太多电流损耗,需要采用多个过孔来将电流从某一层传递到另一层。此外,如果不能在高功率放大器的电源引脚端对它进行充分的去耦,那么高功率噪声将会辐射到整块板上,并带来各种各样的问题。高功率放大器的接地相当关键,并经常需要为其设计一个金属屏蔽罩。       在大多数情况下,同样关键的是确保 RF 输出远离 RF 输入。这也适用于放大器、缓冲器和滤波器。在最坏情况下,如果放大器和缓冲器的输出以适当的相位和振幅反馈到它们的输入端,那么它们就有可能产生自激振荡。在最好情况下,它们将能在任何温度和电压条件下稳定地工作。实际上,它们可能会变得不稳定,并将噪音和互调信号添加到 RF 信号上。       如果射频信号线不得不从滤波器的输入端绕回输出端,这可能会严重损害滤波器的带通特性。为了使输入和输出得到良好的隔离,首先必须在滤波器周围布一圈地,其次滤波器下层区域也要布一块地,并与围绕滤波器的主地连接起来。把需要穿过滤波器的信号线尽可能远离滤波器引脚也是个好方法。此外,整块板上各个地方的接地都要十分小心,否则你可能会在不知不觉之中引入一条你不希望发生的耦合通道。         有时可以选择走单端或平衡 RF 信号线,有关交叉干扰和 EMC/EMI 的原则在这里同样适用。平衡 RF 信号线如果走线正确的话,可以减少噪声和交叉干扰,但是它们的阻抗通常比较高,而且要保持一个合理的线宽以得到一个匹配信号源、走线和负载的阻抗,实际布线可能会有一些困难。       缓冲器可以用来提高隔离效果,因为它可把同一个信号分为两个部分,并用于驱动不同的电路,特别是本振可能需要缓冲器来驱动多个混频器。当混频器在 RF 频率处到达共模隔离状态时,它将无法正常工作。缓冲器可以很好地隔离不同频率处的阻抗变化,从而电路之间不会相互干扰。       缓冲器对设计的帮助很大,它们可以紧跟在需要被驱动电路的后面,从而使高功率输出走线非常短,由于缓冲器的输入信号电平比较低,因此它们不易对板上的其它电路造成干扰。       还有许多非常敏感的信号和控制线需要特别注意,但它们超出了本文探讨的范围,因此本文仅略作论述,不再进行详细说明。       压控振荡器 (VCO) 可将变化的电压转换为变化的频率,这一特性被用于高速频道切换,但它们同样也将控制电压上的微量噪声转换为微小的频率变化,而这就给 RF 信号增加了噪声。总的来说,在这一级以后你再也没有办法从 RF 输出信号中将噪声去掉。那么困难在哪里呢?首先,控制线的期望频宽范围可能从 DC 直到 2MHz ,而通过滤波来去掉这么宽频带的噪声几乎是不可能的;其次, VCO 控制线通常是一个控制频率的反馈回路的一部分,它在很多地方都有可能引入噪声,因此必须非常小心处理 VCO 控制线。       要确保 RF 走线下层的地是实心的,而且所有的元器件都牢固地连到主地上,并与其它可能带来噪声的走线隔离开来。此外,要确保 VCO 的电源已得到充分去耦,由于 VCO 的 RF 输出往往是一个相对较高的电平, VCO 输出信号很容易干扰其它电路,因此必须对 VCO 加以特别注意。事实上, VCO 往往布放在 RF 区域的末端,有时它还需要一个金属屏蔽罩。        谐振电路 ( 一个用于发射机,另一个用于接收机 ) 与 VCO 有关,但也有它自己的特点。简单地讲,谐振电路是一个带有容性二极管的并行谐振电路,它有助于设置 VCO 工作频率和将语音或数据调制到 RF 信号上。       所有 VCO 的设计原则同样适用于谐振电路。由于谐振电路含有数量相当多的元器件、板上分布区域较宽以及通常运行在一个很高的 RF 频率下,因此谐振电路通常对噪声非常敏感。信号通常排列在芯片的相邻脚上,但这些信号引脚又需要与相对较大的电感和电容配合才能工作,这反过来要求这些电感和电容的位置必须靠得很近,并连回到一个对噪声很敏感的控制环路上。要做到这点是不容易的。       自动增益控制 (AGC) 放大器同样是一个容易出问题的地方,不管是发射还是接收电路都会有 AGC 放大器。 AGC 放大器通常能有效地滤掉噪声,不过由于蜂窝电话具备处理发射和接收信号强度快速变化的能力,因此要求 AGC 电路有一个相当宽的带宽,而这使某些关键电路上的 AGC 放大器很容易引入噪声。       设计 AGC 线路必须遵守良好的模拟电路设计技术,而这跟很短的运放输入引脚和很短的反馈路径有关,这两处都必须远离 RF 、 IF 或高速数字信号走线。同样,良好的接地也必不可少,而且芯片的电源必须得到良好的去耦。如果必须要在输入或输出端走一根长线,那么最好是在输出端,通常输出端的阻抗要低得多,而且也不容易感应噪声。通常信号电平越高,就越容易把噪声引入到其它电路。       在所有 PCB 设计中,尽可能将数字电路远离模拟电路是一条总的原则,它同样也适用于 RF PCB 设计。公共模拟地和用于屏蔽和隔开信号线的地通常是同等重要的,问题在于如果没有预见和事先仔细的计划,每次你能在这方面所做的事都很少。因此在设计早期阶段,仔细的计划、考虑周全的元器件布局和彻底的布局评估都非常重要,由于疏忽而引起的设计更改将可能导致一个即将完成的设计又必须推倒重来。这一因疏忽而导致的严重后果,无论如何对你的个人事业发展来说不是一件好事。        同样应使 RF 线路远离模拟线路和一些很关键的数字信号,所有的 RF 走线、焊盘和元件周围应尽可能多填接地铜皮,并尽可能与主地相连。类似面包板的微型过孔构造板在 RF 线路开发阶段很有用,如果你选用了构造板,那么你毋须花费任何开销就可随意使用很多过孔,否则在普通 PCB 板上钻孔将会增加开发成本,而这在大批量生产时会增加成本。        如果 RF 走线必须穿过信号线,那么尽量在它们之间沿着 RF 走线布一层与主地相连的地。如果不可能的话,一定要保证它们是十字交叉的,这可将容性耦合减到最小,同时尽可能在每根 RF 走线周围多布一些地,并把它们连到主地。此外,将并行 RF 走线之间的距离减到最小可以将感性耦合减到最小。        一个实心的整块接地面直接放在表层下第一层时,隔离效果最好,尽管小心一点设计时其它的做法也管用。我曾试过把接地面分成几块来隔离模拟、数字和 RF 线路,但我从未对结果感到满意过,因为最终总是有一些高速信号线要穿过这些分开的地,这不是一件好事。        在 PCB 板的每一层,应布上尽可能多的地,并把它们连到主地面。尽可能把走线靠在一起以增加内部信号层和电源分配层的地块数量,并适当调整走线以便你能将地连接过孔布置到表层上的隔离地块。应当避免在 PCB 各层上生成游离地,因为它们会像一个小天线那样拾取或注入噪音。在大多数情况下,如果你不能把它们连到主地,那么你最好把它们去掉。