在线座谈

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关于本次座谈

座谈简介

本次在线座谈将以一款基站基础设施收发器设计实例,对本话题进行深入的讨论。该研讨会将详细阐述诸如增益、噪声系数和输入三阶截取等性能衡量指标对总体接收器性能的影响,并演示凌特公司从RF前端到高速ADC的三芯片解决方案,来满足基站接收器设计的苛刻动态范围要求。在发送器方面,凌特推出的高性能上变频混频器系列产品同样可在未牺牲系统性能的情况下使发送器设计大为简化。通过谨慎选择上变频混频器的输出功率便能够容易地对其进行优化,以满足诸如多载波W-CDMA系统应用上非常严格的发送频谱要求。

精彩问答

主题: 高性能 RF 单元式部件简化了基站收发器系统设计
在线问答:
[问:chenzezong] 包含AD转换器在内的接收部分的灵敏度、动态范围如何计算? 
[答:MinZou] Fisrt,calculate effective NF of ADC based on the presnetation and do rx chain analysis.  [2004-7-28 10:43:43]
[问:caesar_ye] 在接收系统中,如何处理由于LO泄漏引起的直流漂移。尤其当采用了结构上的屏蔽措施以后? 
[答:Vlad] There are two types of DC drift or DC offset in direct conversion receiver:1. Static DC offset. Can be corrected by DC level shift, and/or AC coupling can be used.2. Dynamic DC offset. Can be corrected by a feedback loop or AC coupling can be used.  [2004-7-28 10:46:23]
[问:chenzezong] 1:高频段直接采样是否可行?技术指标(如灵敏度、动态范围)大概能达到多少? 
[答:MinZou] The higher freq, the more demanding ADC will be needed. LT1750 is the one of fastest 14-bit ADC in the industry. ADCs ususally have best performance at low freq.  [2004-7-28 10:46:54]
[问:王长明] 贵公司的有源混频器比起常用的无源混频器有何技术优势,对系统指标有哪些有利和不利因素?谢谢!! 
[答:MinZou] Easy system implementation with less external components. Comparable RF performances. Less LO drive and leakage. Lower system cost.  [2004-7-28 10:49:07]
[问:Dr. Wu] 我们一直在基站系统设计中使用无源上变频混频器和下变频混频器。我们采用非常高的LO功率电平来驱动混频器。LO功率电平可高至+13dBm。但是,为什么有源混频器的LO驱动功率电平却可低至-10dBm? 
[答:MinZou] 由于我们的有源混频器开关晶体管是预偏置的,只需200mV的电压摆幅就足以对双极型晶体管进行接通或关断操作以生成期望的混频分量。但对于无源混频器而言,则需要高于1V的电压摆幅。此外,有源混频器通常都具有内置LO缓冲器。这使得LO驱动电平进一步降低。  [2004-7-28 10:50:00]
[问:maodengzhang] 对于RF信号宽范围可调有没有什么好方法。譬如信号从20M--120M连续可调。用DDS设计RF信号源目前最高能到多少Hz?对于RF信号功率放大只能用MOSFET三极管吗? 
[答:MinZou] Large freq span from 20M-120M may post a challenge for VCO design (i.e. Varactor voltage tuning). RF PAs use LDMOS, GaAs and Bipolar.  [2004-7-28 10:52:08]
[问:zhao_sl] 该收发器仅适用于基站不适用于移动站吗? 
[答:Terry] the receiver architecture we introduced here is mainly for base station. The products are also mainly targeted for base station application.  [2004-7-28 10:52:13]
[问:Dr. Wu] 为什么贵公司的有源混频器具有如此优良的泄漏性能(比如LO至IF和LO至RF)? 
[答:MinZou] 这是因为我们采用了所谓“双平衡混频器”拓扑结构。LO泄漏表现为偶次分量,它在混频器内部被差分消除。这样,我们的有源混频器就拥有了超群的LO至IF和LO至RF泄漏性能。  [2004-7-28 10:53:00]
[问:lixuechu] 无线系统中,镜频信号跟有用信号的功率之比有多大?怎样确定系统所需镜频抑制比(Image rejection ratio,IRR)的大小? 
[答:James] In a transmitter, assuming you are using an upconverting mixer, you will have the output signal plus the image, both are at the same power. However, if an image-reject mixer is used, the image will be reduced depending on the image rejection capability of the mixer. Then an output filter can attenuate the image more. In a receiver, the filter is at the input, thus the image is reduced before feeding the downconversion mixer.  [2004-7-28 10:54:19]
[问:Dr. Wu] 您刚才提到,对于传统的超外差接收器来说,通道选择是紧接在混频器之后进行的。对于采用数字IF的高性能接收器而言,通道选择具体是在何处完成的? 
[答:MinZou] 通道选择是在DSP中进行的。在利用ADC进行IF数字化之后,数字IF被进一步解调为数字I和Q基带信号,然后借助数字滤波器来完成通道选择。数字滤波器可针对多模式操作进行编程。  [2004-7-28 10:57:00]
[问:mjk1230] 变频器为什么要另加控制电源? 
[答:Terry] I think the question is asking about the power supply used for the mixer. Our product is an active mixer so we need power to pre-bias the circuits.  [2004-7-28 10:58:37]
[问:bywen] 请问:1、基站收发器中,接收系统的动态范围、灵敏度指标一般是多少?不同制式的基站,对这些指标的要求是否不同?2、这些RF器件是否可以用于雷达设备?这些器件的最低可用频率是多少? 
[答:MinZou] 1. It depends. On the seminar, I gave an example of medium BS. In this case, the sensitivity is about -174+10log3.84M+NF+6(S/N). Normally you want to minimize the NF. So for a given BW, the sensitivity requirement is quite similar. 2. Down-converting mixers and power detects such as LT5509 and LT5534.  [2004-7-28 10:59:15]
[问:daogla] 谨慎选择上变频混频器的输出功率便能够容易地对其进行优化,以满足诸如多载波W-CDMA系统应用上非常严格的发送频谱要求。请问怎样情况才是您所说的“谨慎”? 
[答:James] The output power should be selected based on the mixer"s mininum noise and maximum ACPR performance.  Typical mixer datasheet should have performance characteristics curves that allow you to choose the best operating point.  [2004-7-28 10:59:38]
[问:chenzezong] 目前,不采用AGC等控制增益技术,要求高频段的灵敏度达到-100dBm,动态范围最大能做到多少? 
[答:Vlad] Assumptions:1. receiver needs 100 dB of gain to bring -100 dBm input signal to a level of 0 dBm to the input of the A/D converter.2. 14-bit A/D converter is used (78 dB dynamic range).3. Output Signal/Noise ratio = 10 dB min.4. Receiver Noise Figure = 5 dB.In this case dynamic range of the receiver without AGC will be 63 dB, considering the receiver will have intermodulation products -80 dBc or better.  [2004-7-28 11:00:57]
[问:安飞] 是不是采用零中频设计方案?PLL和VCO是不是在片内集成?我不知道FR单元的概况,请介绍。 
[答:MinZou] We have LT5515, LT5516 and LT5517 designed for zero IF rx. External VCO and PLL are needed.  [2004-7-28 11:01:13]
[问:Dr. Wu] 我们能否在传统的超外差接收器中实现多模式操作? 
[答:MinZou] 不行。在该架构中,IF信道选择滤波器具有一个针对其特定应用的通道带宽而精确调谐的频率响应。由于IF通道选择滤波器缺乏灵活性,因而将接收器硬件限制为单一模式。  [2004-7-28 11:03:00]
[问:Gforce] Linear在基站收发器系统中如何来保证发送和接收性能的稳定性? 
[答:James] All our products are carefully characterized and evaluated in various operating circuits  under different temperature conditions, and over multiple lots of wafer to ensure consistent behaviors.  Further more all our products go through extensive burn-in over time and temperature as part of our standard reliability test procedure.  All parts are tested against datasheet specifications.  [2004-7-28 11:05:01]
[问:bluebear] 数字IF有何优点?它的损耗有多高?是否采用零IF? 
[答:Terry] zero IF is not the same idea as digital IF. In zero IF system, the signal is directly converted down to baseband. For digital IF, we just convert the signal down to a specific IF (say 140MHz) and then sample the signal idrectly with high speed ADC. By doing so, no channel selection filter is needed as channel selection is done in digital domain.  [2004-7-28 11:05:29]
[问:Dr. Wu] 当您比较不同的上变频混频器性能时,OIP3是不是一个比IIP3更好的参数? 
[答:MinZou] 是的。在发送器系统设计中,我们演示了W-CDMA应用的单变换发送器架构。由本例可见,在一个给定的输出功率,对ACPR有着一个非常严格的要求。OIP3与输出功率和ACPR是直接相关,可更有效地表达发送器系统的要求。  [2004-7-28 11:07:00]
[问:flyrain] Linear 能否提供接收系统和发送系统所需的全部器件?能否提供完整的解决方案? 
[答:Terry] I"m sorry that we just provide the building blocks components.  [2004-7-28 11:07:15]
[问:chenzezong] 在高频段,采用零中频方案,灵敏度、动态范围能达到多少?技术难度如何? 
[答:Vlad] Sensitivity of the direct conversion receiver depends for the most part on the Low Noise Amplifier (LNA) gain in a front of the I/Q mixers.Dynamic range of the direct conversion receiver depends on linearity of all the receiver stages.The biggest problems are static and dynamic DC offset at the baseband outputs when DC coupling is used. For that reasons BB gain should be minimized.  [2004-7-28 11:07:47]
[问:Gforce] 发送功率检测和功率控制,Linear有何好的方案?采用何种器件? 
[答:MinZou] Linear has many best RF power detectors availabe in the market such as LT5505, LT5509, LT5532 and LT5534.   [2004-7-28 11:09:42]
[问:daogla] LO是什么意思?LO和RF如何混频起来? 
[答:Terry] LO means local oscillator. For up-mixer, we convert the IF signal to RF with Frquency of RF equals to Flo+Fif or Flo-Fif  [2004-7-28 11:11:55]
[问:Dr. Wu] 我们能否把LT5522(或LT5521)兼用作上变频和下变频混频器? 
[答:MinZou] LT5522专为在下变频应用中实现最佳的RF性能进行了优化。在内部使LO端口和RF端口与50 Ohm阻抗相匹配。无需使用外部匹配组件。在RF端口上,单端至差分转换是利用内置变压器来完成的。在系统应用中只需要6个外部组件。LT5521则专为在上变频应用中实现最佳的RF性能实施了优化。NF和OIP3被精确地优化,而且LO至RF泄漏被减至最小,旨在解决RF通路中的LO滤波问题。  [2004-7-28 11:13:00]
[问:marximzbg@163.net] 请问:贵公司对于基站收发器系统设计能提供哪些技术支持? 
[答:MinZou] Application and technical supports are Linear"s strength. We provide our IC application supports as well as some system designs assocaited with our ICs.  [2004-7-28 11:15:08]
[问:flyrain] 基站的可靠性要求很高,在设计时如何考虑到这一点? 
[答:Vlad] High reliability in a circuit design can be achieved by using ICs and all other components at recommended values. For example, an IC is used at maximum of the supply voltage, then this may lead to reliability degradation.In a system design, engineers should add some margins for critical parameters. The most critical circuits should be redundant.  [2004-7-28 11:16:27]
[问:bluebear] 接收器中的ADC速度要求有多高?Linear的那种ADC产品能用在这里? 
[答:Terry] It depends on the IF frequency and your sampling technique. LTC has a family of high speed ADC that may fit your requirement. Please contact eli@linear.com for more details.  [2004-7-28 11:17:11]
[问:Dr. Wu] 对于像 LT5534 这样的对数放大器检波器,如果我们在总功率的条件下采用一个单音信号和一个双音信号对其进行测试,它会不会产生不同的输出? 
[答:MinZou] LT5534 是一款基于对数放大器的峰值检波器。对于一个确定的输出功率,具有不同峰值因数的不同波形输出将始终具有一个略带几分 DC 特征的输出电压。  [2004-7-28 11:18:00]
[问:marximzbg] 该收发器最大支持的射频信号范围是多少?能支持到多少G? 
[答:Terry] We have different parts that support different frequency range. You may contact eli@linear.com for more details.  [2004-7-28 11:20:30]
[问:smartboy88] 影响RF性能的因素主要是什么? 
[答:MinZou] On the seminar, we just covered one of the most important parameter SFDR (Distortion and noise performance). Besides, proper islolation and filtering are important. The performance of IC components and system design are important.  [2004-7-28 11:20:53]
[问:Dr. Wu] 当我们改变用于 CDMA 的代码时,LT5534 会不会给出不同的读数? 
[答:Terry] 这取决于平均波形的平均因数和波峰因数。对于一个给定的 RF 输入功率电平,如果平均波形的峰值因数保持不变,则输出保持不变。  [2004-7-28 11:21:00]
[问:deadlessbird] PCB的布局对RF部分有何特别的要求?如何和其它部分隔离?需要屏蔽吗? 
[答:James] Use ground plane extensively.  Use enough ground vias to connect ground planes in different layers.  Keep RF transmission lines as short as possible.Keep RF transmission lines only on the top and bottom layer whenever possible, and use solid ground plane under transmission lines.Avoid sharp angles in RF lines to reduce radiation.  Use mitered angle for turns.Maintain proper ground keep-out to ensure line impedances.Shielding maybe required depending on surrounding emmissions and sensitivity to interference or if undesired radiation needs to be controlled.  [2004-7-28 11:21:03]
[问:marximzbg] 贵公司在中国有分公司吗?能提供哪些技术支持? 
[答:Terry] Yes, we have office in Hong Kong, Shenzhen, Shanghai and Beijing. Besides, we also have 2 distributors - Cytech and Unique. These two companies also have many office all over China. You an visit our website www.linear.com.cn for their exact location.  [2004-7-28 11:22:14]
[问:marximzbg] 请举例该收发器目前在中国和世界有哪些应用吗? 
[答:James] We maintain confidentiality of all our customers, therefore we cannot name names.  However, many leading basestation manufacturers in Scandinavia, Europe, US, Japan, and China use our products.  [2004-7-28 11:24:07]
[问:iaag] LT5506 的输出幅度 在100-200mv 时,输出无杂谱,一旦超过 200mv 杂谱随着输出的增加 ,越来越大。 
[答:Vlad] With the input levels at 200 mV and higher no noise should be observed at the baseband outputs.The LT5506 data sheet specify input level -79 to -22 dBm. Higher signal levels can be applied with appropriate gain control. If gain control voltage set for too much gain the output signal will be clipped. If gain control voltage set for too low gain the oputput signal will be lower amplitude and a some noise can be observed.  [2004-7-28 11:24:33]
[问:Dr. Wu] LT5521 的 RF 和 IF 平衡-不平衡变压器的设计准则是什么? 
[答:Terry] 片上变压器的外形尺寸与工作频率成反比。频率越高,变压器就会越小。当频率低于几百 MHz 时,在芯片内部集成如此大的变压器既不实用,也不经济。此外,在采用大尺寸变压器的场合,IF 和 RF 之间的耦合也是一个约束条件。  [2004-7-28 11:25:59]
[问:prof_duan] 请问LT有无大功率RF发射解决方案? 
[答:Terry] Our products are mainly on mixers, IF amplifiers, power detectors, active filters, ADC, modulators and demodulators. All these components are the building blocks for tranceivers regardless of the power level. In other words, these parts can also be used in very high power design.  [2004-7-28 11:27:42]
[问:greatmin] 有源混频器比之无源混频器的可靠性如何? 
[答:MinZou] On all our active ICs, we have ESD protection. Therefore, our reliability is good. Who makes the parts is important too. Linear has best reputation in realibity and quality control. All our products are not released  without strict realibility and life time test.  [2004-7-28 11:28:27]
[问:smartboy88] RF部分对电源有和要求? 
[答:Vlad] The power supply should be clean and low noise.  Good quality ceramic capacitors should be used for supply bypass right at the RF component supply pins.  [2004-7-28 11:28:34]
[问:Dr. Wu] 在 RFin = 1800、LO = 2700 和 RFout = 900MHz 的情况下,我能不能将 LT5521 用作下变频混频器?预计在规格会出现怎样的劣化? 
[答:Terry] LT5521 专为上变频混频器应用进行了优化。LT5512 适用于该工作频率范围。  [2004-7-28 11:29:59]
[问:lydslpxian] linear能否根据客户要求,提供完整的解决方案? 
[答:Terry] We can help suggesting the necessary design approach and provide solutions but it depends on the level of solution required. LTC is not involved in digital domain so we can only help suggesting the analog portion of the system.  [2004-7-28 11:30:07]
[问:jackboyer@126.com] 设计无线数传系统如何选择贵公司的WCDMA收发器芯片?给出一个SAMPLE?! 
[答:Terry] You can provide us your requirement and we can discuss the design detail together. Please contact eli@linear.com  [2004-7-28 11:31:34]
[问:deadlessbird] Linear接收器的灵敏度能达到多高? 
[答:Vlad] The sensitivity of a receiver depends on the cascaded gain and noise figure of the entire receiver signal chain including the LNA at the front end.  [2004-7-28 11:32:14]
[问:prof_duan] How does LT provide high power RF solution?Thanks! 
[答:Terry] We don"t provide high power components. However, we do provide many of the building blocks of the RF systems like mixers, active mixers, IF amplifiers, power detectors, modulators and demodulators.  [2004-7-28 11:32:34]
[问:lhk2008hf] 电源的旁路电容多大较为合适?采用那种电容能满足RF性能? 
[答:MinZou] It depends the lowest operating frequency. Sometimes serveral capacitors with different values are connected in parallel in order to filter out all signals incuding high freq signals. (The lower value cap needs to have high resonant freq).  [2004-7-28 11:32:51]
[问:daogla] 贵公司这类产品性价比是不是目前是很具有竞争力的? 
[答:Terry] Yes, of course.  [2004-7-28 11:33:18]
[问:RobinYoung] 有没有一款能够对功率低至 –83dBm 且动态范围为 30dB 的 RF 信号进行检波的 RF 检波器? 
[答:MinZou] 当在 LT5534 的输入端上采用窄带匹配时,可检波信号的功率可低至 –75dBm。为了对 –83dBm 的信号进行检波,可以在它前面采用具有几个 dB 增益的部件以实现该灵敏度。  [2004-7-28 11:34:59]
[问:marximzbg] 中国移动和中国联通的基站设备有没有使用LINEAR的产品呢? 
[答:Terry] We don"t deal directly with service providers but their equipment manufacturers. However, our products are widely adopted by all the big telecom equipment manufaturers in the world, including China.  [2004-7-28 11:35:13]
[问:felix2002] 基站收发器系统的主流是什么? 
[答:James] The main trends for the basestation transceiver designs:1. Single frequency conversion block converting receivers where IF is digitized. These receivers usually  used for digitizing several uplink channels.2. Direct conversion receivers to baseband. These receivers used for single channel.3. Direct conversion transmitters. These transmitters can be used for single and multiple channels.4. The trend is to incorporate active mixers in all receiver and transmitter designs.  [2004-7-28 11:35:42]
[问:rfapc] 如何实现LO-IF的低漏泄?匹配网路如何设计? 
[答:MinZou] On our active mixers, we use "double-balanced" topology. The LO at IF appears as even-mode mixing products. They are cancelled out inside our chips. Thefore we have very low LO-to-IF leakage.Our active mixers have good port-to-port isloations, the matching networks can be designed independently.  [2004-7-28 11:36:46]
[问:reporter] LT5516 具有高共模偏移电压,需要采用一个变压器来把输出变为单端信号。在中国,变压器是一个很麻烦的部件。如果我仍然不得不获取低频信号,怎样才能不用变压器? 
[答:Terry] 为了保持该器件的卓越性能,需要采用差分输出。如果其后的基带组件采用的是差分输入,则可直接连接 LT5516 的差分输出。  [2004-7-28 11:36:59]
[问:RobinYoung] 在无源解决方案中,您如何评价凌特的混频器产品所处的地位?在有源解决方案中的地位又如何?贵公司采用何种类型的工艺和结构使得自己的产品与众不同? 
[答:MinZou] 在此次研讨会上,我们已经论述了有源解决方案相对无源解决方案在系统设计容易、外部组件数量小以及 LO 泄漏非常低等方面的优势。我们日益明显地感觉到,有源解决方案正凭借其所具备的诸多优点而受到起来越多系统制造商垂青。目前,我们正在致力于进一步提升器件的 RF 性能并减少外部组件的用量,以满足客户的需要。我们并不依赖于芯片代工厂的制造工艺。我们拥有优秀的工艺队伍,他们正在开发属于我公司的高速 RF 双极型工艺。因此,不管半导体工业处于其发展周期的哪一个阶段,我们都能够保持自己的产品交货时间不受影响。   [2004-7-28 11:37:59]
[问:reporter] 在我们的印象中,凌特并不是一家RF公司,只是不久以前才进入这一领域,在与诸如RFMD等传统的RF公司的竞争中,你们拥有哪些优势和技术专长? 
[答:MinZou] 我们的目标是高性能以及适合的应用,而避开常规产品。我们拥有业界最佳的 RF/模拟设计队伍和销售团队。我们深知用户的需要。 · RFIC 只是对我公司已有的高性能模拟产品库的一个自然的扩充 · 我公司是世界上首屈一指的高性能模拟产品供应商 · 在高质量产品控制中声誉卓著 · 销售人员全部都是拥有技术职称的工程师 · 大量的技术和应用支持 · 我们有大量的产品供应无线通信市场,例如:电源管理芯片、运算放大器、滤波器、热插拔电源控制器、ADC和DAC等   [2004-7-28 11:38:59]
[问:marximzbg@163.net] 贵公司的RF器件除了在基站领域,还在哪些领域有应用呢? 
[答:Terry] We do have some parts that are are good for cell phone, WLAN, DVB, CATV and optical data network.  [2004-7-28 11:39:41]
[问:chenzezong] 中频数字接收机采用过采样技术,能带来一定的处理增益,能降低量化噪声功率,但不能降低系统热噪声,因而对输出SNR并未降低许多,是否? 
[答:MinZou] Yes, oversampling has processing gain. But it will not reduce the thermal noise caused by the components.  [2004-7-28 11:39:47]
[问:RobinYoung] 就 LT5522 和 LT5519 而言,它们在 450MHz RF 频段的性能如何? 
[答:MinZou] LT5522 和 LT5519 分别针对下变频混频器应用和上变频混频器应用进行了优化。这两款器件在 RF 端口上均设有片上变压器。因此,它们适合于较高 RF 频率的应用。对于 450MHz 应用,我们建议客户使用不带片上变压器的 LT5512 和 LT5521。  [2004-7-28 11:39:59]
[问:reporter] 对于 LT5521,凌特是否准备将 RF 平衡-不平衡变压器集成进去并使其与 LT5520 引脚兼容? 
[答:Terry] 在设计产品时,我们的策略是在兼顾兼容性的同时力争实现最佳的电路性能。如果引脚兼容性确有意义,我们将在不牺牲性能的情况下完成这一目标。   [2004-7-28 11:41:59]
[问:mrli] 请介绍发送器系统的线性性能?它和那些因素有关?如何提高它的线性度? 
[答:MinZou] The OIP3 of up-converting mixer LT5521 is 23.2dBm at 1900MHz. The excellent linearity is achived through good circuit design and fast in-house IC process.   [2004-7-28 11:43:34]
[问:RobinYoung] LT5515/5516/5517 这几款器件彼此之间是否具有引脚兼容性? 
[答:Terry] LT5515 和 LT5516 的引脚完全兼容。LT5517 采用单端 2XLO 和内部 50 Ohm 匹配,因此其引脚与前面两款器件是不兼容的。  [2004-7-28 11:44:59]
[问:ladawang] 我认为基站设备的稳定性比先进性更为重要,烦请介绍成功案例。 
[答:James] Yes, reliability is an important design goal. An example is the LT5522 downconverting mixer has been designed into a major basestation manufacturer"s system not only because it has the required performance, but also has a high ESD voltage rating. The LT5522 was designed in place of a GaAs mixer having low ESD rating, which caused manufacturing and field failures.  [2004-7-28 11:45:14]
[问:rfapc] 使用LT5522时,IF低于140MHz,为什要加接变压器?对变压器有和要求?那种产品较好? 
[答:Vlad] The are two main purposes for the transformer:1). Differential to single-ended conversion2). Provide DC supply to open-collector IF output amplifier through the transformer center tap.If the output of the LT5522 will be used differetially, this transformer is not needed.  However, pull-up inductors will be required to provide DC power.For single-ended applications, choose a transformer with a center tap on the high impedance side.  The LT5522 IF output can be roughly modeled as a 400-ohm resistor in parallel with a 1pF capacitor.  Thus, an 8:1 impedance ratio transformer would be ideal.  A good candidate is Mini-circuit"s TC8-1.  At higher frequencies, 8:1 transformers are not readily available.  A 4:1 transformer, such as M/A-Com ETC4-1-2 can be used with some series inductors as shown in the datasheet.  [2004-7-28 11:45:31]
[问:reporter] LT5514 是一款上佳的器件,但我们需要一个 0.5dB 的增益控制步进,凌特今后是否将加以调整? 
[答:Terry] 客户的反馈意见对我们是非常重要的。我们会考虑您的提议。  [2004-7-28 11:46:59]
[问:mrli] 接收器的噪音和那些因素有关?在PCB和元件选择上要注意什么事项? 
[答:MinZou] The NF of rx mainly is determined by the loss of filter after anttena and NF of LNA. The NF of down-converting mixer and gain of LNA need to be chosen properly.   [2004-7-28 11:47:22]
[问:nyebob] 请问在这些有源收发器中,电源的稳定性要求如何,器件中有特别的处理么?谢谢 
[答:James] For active mixers clean power supply (free of any noise) should be used. Power supply output should be filtered using low pass filters. Bypass capacitors should be used at supply voltage pins of the mixer ICs.  [2004-7-28 11:48:57]
[问:Vincentding] 请问你们的混频器指标中有无IP2? 
[答:James] Most of our mixer IC products have IP2 specification in our data sheets.  [2004-7-28 11:51:06]
[问:Sam Ya] I"d like to use LTC1566-1 as I/Q LPF after LTC5515, but the dc bias voltage of 5515 output is 4.15V, 1566-1 requires 2.5V for best performance, how to do dc level shifting? 
[答:MinZou] For full-duplex system, AC coupling can be used.For half-duplex system, addtional components are needed and we can provide detailed application support for the DC coupling.  [2004-7-28 11:51:40]
[问:marximzbg@163.net] RF设计应该注意和考虑哪些问题呢? 
[答:Vlad] Some of the RF design considerations and concerns are manufacturability, reliablitity, cost, and performance.  [2004-7-28 11:52:48]
[问:cdliutong] 请问凌特公司的RF在消除有害干扰和噪声有什么的特长? 
[答:MinZou] Excellent linearity (IP3 and IP2) of RF components will pretect the desirable weak signal among strong interference, which can be filtered out in the later signal processing. Our parts have good linearity and low noise figure.  [2004-7-28 11:56:30]
[问:lawrence.shi] 有源混频的性能一定优于无源混频的性能吗? 
[答:James] Active mixers have better port to port isolation, need lower local oscillator drive and have lower conversion loss. Some active mixers have conversion gain.For some wireless infrastructure applications and most of the cable infrastructure applications high level passive mixers can not be used because of the high local oscillator signal leakage into other ports of the mixer.  [2004-7-28 11:58:21]
[问:Vincentding] 你们混频器的电源的纹波要求是多少,是如何计算的? 
[答:Vlad] Good circuit design should use clean power supplies, with minimum ripple.  Actual requirement depends on the system.  Use good RF bypass capacitors at the IC supply pins.  The power supply output should also be filtered.  [2004-7-28 12:00:06]
[问:mrli] 如何确定滤波器的参数?如何选择所用的LC元件? 
[答:Vlad] The LC constant determines the filtering frequency.  The self-resonant frequencies of the individual components should be considered as part of the total consideration.  [2004-7-28 12:04:34]