[问答]

测量混频器NF时的结果很奇怪

问答对人有帮助，内容完整，我也想知道答案 0 大家好，我准备描述我使用我的CXA系列SA制造的CMOS混频器，但首先我试图使用简单的现成混频器，小型电路的ADE-1L来处理变频器NF测量。 RF频率为65MHz，IF为15MHz，LO为80MHz。我已经测量了在这些条件下的转换增益约为5.35 dB（使用合成器给出LO功率pf + 4dB，RF功率为-20dB），而不是噪声系数测量的计算增益），这非常接近指定的增益在器件数据表中。我现在的设置如下：LO由来自模拟设备的CN0285合成器开发板驱动。 LO通过35MHz HPF，然后通过3dB衰减器，为混频器提供+ 4dBm。 IF端口传递到7阶20MHz低通滤波器（以消除LO馈通）。我没有SA的前置放大器选项，因此我使用自己的外部前置放大器，HD26316，然后是10-15dB的衰减。在RF端口上，我在进行DSB测量时直接连接噪声源（346A）。对于LSB测量，我可以使用65MHz BPF来消除上边带。根据我是否使用LSB或DSB测量，问题我得到了一些相互矛盾的测量。如果我使用DSB，我得到G = -1.5dB和NF = 1.5dB。 G和NF大约相等是好的，但它们应该在-2.2 dB左右（比测量的转换增益高3dB）。如果我将测量值更改为LSB，而不在RF端口上添加滤波器，我会得到完全相同的结果，这是令人惊讶的。如果我然后在RF端口上添加65MHz BPF（并将其2.5dB的衰减输入到损耗补偿中），那么我得到G = -6.0dB和NF = 6.9dB。所以现在增益太低，而且NF远大于预期。如果我将LO功率降低3dB，我可以得到G = -5.8dB和NF = -6.3dB。所以这两种测量都没有给我一个令人信服的结果，即使只是为了获得。降低LO功率的事实增加了G（当我用合成器测量增益时不会发生这种情况）向我暗示某些东西正在破坏噪声测量。我估计我的NF不确定度大约是0.4dB，所以这还不足以解释这种差异。但是我对如何追踪错误来源的想法已经不多了。系统的每个部分都是屏蔽的，到目前为止，当关闭其他附近的仪器时，我还没有看到任何重大变化。有什么建议？以上来自于谷歌翻译以下为原文 Hello all, I am preparing to characterize a CMOS mixer I've fabricated using my CXA series SA, but first I am trying to get a handle on frequency converter NF measurements using a simple off the shelf mixer, the ADE-1L from minicircuits. The RF frequency for this will be 65MHz, IF will be 15MHz, and LO will be 80MHz. I've measured the conversion gain under these conditions to be about 5.35 dB (using synthesizers to give LO power pf +4dB and RF power of -20dB), not the noise figure measurement's calculated gain), which is very close to the gain specified in the device datasheet. My setup right now is as follows: The LO is driven from a CN0285 synthesizer dev board from analog devices. The LO passes through a 35MHz HPF and then a 3dB attenuator to give +4dBm to the mixer. The IF port passes to a 7th order 20MHz lowpass filter (to kill the LO feedthrough). I don't have the SA's preamp option, so I use my own external preamp, a HD26316 followed by 10-15dB of attenuation. On the RF port, I connect the noise source (346A) directly when doing DSB measurements. For LSB measurements I can use a 65MHz BPF to eliminate the upper sideband. The issue I'm getting somewhat contradictory measurements depending on whether I use LSB or DSB measurements. If I use DSB, I get G=-1.5dB and NF=1.5dB. It's good that G and NF are about equal, but they should be about -2.2 dB (3dB above the measured conversion gain). If I change the measurement to LSB, without adding the filter on the RF port, I get the exact same results, which is surprising. If I then add the 65MHz BPF on the RF port (and input its attenuation of 2.5dB into the loss compensation) then I get G=-6.0dB and NF=6.9dB. So now the gain is too low, and the NF is much greater than expected. If I back the LO power down by 3dB, I can get G=-5.8dB and NF=-6.3dB. So neither measurement gives me a convincing result, even for just the gain. The fact that lowering the LO power increased G (which doesn't happen when I measure gain with my synthesizers) suggests to me that something is corrupting the noise measurements. I've estimated my NF uncertainty to be about 0.4dB, so that's not enough to account for the discrepancy. But I'm running out of ideas on how to track down the source of the error. Every part of the system is shielded, and so far I haven't been able to see any significant changes when shutting off other nearby instruments. Any recommendations? 0
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答案对人有帮助，有参考价值 0 在混频器NF上进行良好测量非常困难。您可能没有考虑到的一些因素：如果混频器本身是宽频带，那么即使使用滤波器，也可能在滤波器带外存在伪通带（通常高于3次谐波），这可能允许信号通过通过调音台。噪声源是宽带，噪声功率高达GHz。混频器的增益主要取决于测量输出端的热噪声功率，并了解噪声源ENR，计算产生热噪声功率的增益。如果来自噪声源的带外信号通过滤波器和转换器到达IF，则可能导致增益过高，并且NF看起来很低。非常常见。对此的最佳解决方案是进行冷噪声测量，仅测量混频器输出端的冷噪声功率，并在输入端具有良好的负载。然后测量增益（VNA最好但可以用sig gen和SA完成）并将NF计算为相对噪声功率（噪声功率高于ktB），单位为dB，除以dB的增益。混频器测量中的其他非常大的误差源是来自LO的近端和带外噪声进入IF的输出并导致噪声功率读数出错（如果LO不是用于的那个）最后使用混合器）。以上来自于谷歌翻译以下为原文 It's very hard to make good measurements on mixer NF. Some elements you might not have accounted for: If the mixer itself is broad band, then it is possible that even with your filters, there are spurious pas***ands out of band of your filter (typically above the 3rd harmonic) that can allow signal to pass through the mixer. The noise source is broadband, and has noise power out to many GHz. The gain of the mixer is essentially determined by measuring the hot noise power at the output, and knowing the noise source ENR, computing the gain that gives that hot noise power. If out of band signal from the noise source passes through your filters and converters to the IF, it can cause the gain to appear too high, and the NF to appear to low. Very very common. Best solution for this is to do cold noise measurements, measuring only the cold noise power at the output of your mixer with a good load on the input. then measure the gain (VNA is best but can be done with a sig gen and SA) and compute the NF as Relative Noise Power (noise power above ktB) in dB, divided by gain in dB. other very big sources of error in mixer measurements is close-in and out-of-band noise from the LO getting onto the output of the IF and causing the noise power reading to be in error (if the LO is not the one intended for final use of the mixer).

2018-10-15 11:28:28 评论举报孔德羲