Hi Tim, my apologies for the long delay in responding. We just heard back from the factory: "Our DMMs will not support the Excel add-in except the old one in 32-bit running under Windows XP. We are sorry for this inconvenience."

A VNA is capable, but using 2 measurements, short and open. See this article: https://www.edn.com/simple-trick-to-measure-plane-impedance-with-a-vna/ A TDR is a more direct measurement, using our J2154A and an oscilloscope: https://www.signalintegrityjournal.com/articles/1852-the-goldilocks-tdr

Hi Tim, thank you for your post. We are looking into this and will get back to you as soon as possible.

The B-AMP 12 Amplifier (https://www.picotest.com/products_OL000168.html external power amplifier for the Bode 100) is used to amplify the Bode 100 output signal by 12 dB. It is primarily for PDN, and specifically for ultra-low impedance power rails. The P2102A/P2104A PDN probes work with, or without, the B-AMP, but all PDN measurements are mostly dependent on the cable resistance and the CMRR of the isolator (e.g., J2102B). In fact, in the University paper (https://www.picotest.com/measurements/download/UNIVERSITY_How_to_Measure_Ultra_Low_Impedance_(100uOhm_and_lower)_PDNsVersion17b.pdf ) we showed the impedance error can essentially be reduced to Rshield/CMRR. We also showed that a source power amp is the ONLY way to improve the SNR of the measurement, but has no impact at all on measurement accuracy, only on SNR (noise). Ben Dannan (https://www.linkedin.com/in/benjamin-dannan/) showed the benefit of the B-AMP12 for measuring COT converters, which are typically noisy. That is where the SR issue comes from. Without VRM noise there is no need at all for a B-AMP12, but since the VRM noise raises the noise floor, the signal needs to be increased to maintain a given SNR. That is what the B-AMP12 does. The Bode 100 inputs can tolerate an absolute max voltage of 5Vrms but the recommended is below 3.3Vrms. The +13dBm source power is 1Vrms so at the output of the B-AMP12 the signal is 4V, not including the DC voltage of the rail being measured. It is VERY easy to damage the front end. Oscilloscopes typically have a maximum rating of 2.5Vrms, so even easier to blow out the front end. Having done it twice, in two different brand scopes, I can tell you that all channels are generally on a single board. Each scope repair cost more than $6K, so be careful. I hope it is clear that the B-AMP12 is not a replacement for the PDN browser probes. So, comparing them as interchangeable does not make sense. The B-AMP can produce a cleaner plot for noisy power rails or ultra-low impedance (our record is 22uOhm, but Ben Dannan just demonstrated 4uOhms, using B-AMP12). This improvement would be the same with soldered cables or probes and accuracy would not be noticeably affected in either case. In most cases, an oscilloscope offers better noise performance for measuring PDN impedance and so doesn’t require an amplifier. On the E5061B ENA we demonstrated a 22uOhms measurement, without a power amp despite the instrument being limited to +5dBm. So, the only reason we could see for you to add a B-AMP12 is to overcome a noisy output, but beware that you can cause damage with it if you measure with too large a signal (as in impedance above a few Ohms).

Precisely! One tip I often give is for cleaner plots, use fewer datapoints. I think I mentioned this in my online classes too. This does trade-off definition, but you’ll lose some definition in the peaks (that you didn’t want) and also fewer datapoints mean more interpolation, which includes smoothing. Q(Tg) is related to the phase slope, so the higher the Q the steeper the slope, or the steeper the slope the higher the Q. Often these noise blips are due to external noise – for example maybe the noise from LED lighting or fluorescent lights, noise from other circuits in the system, etc. In rare cases, they are because the system is oscillating. Even poor phase margin does not create such a narrow “spur” but an oscillation can. Most of these noise blips are external, they may also be there when the power is OFF, confirming you can ignore it. In any case, store the OFF measurement in memory and then look at the ON measurement. You are interested in where the two curves converge, and in the case of poor stability, the ON impedance will be greater than the OFF impedance. It IS possible for these blips to be stability related, so I am NOT telling you to ignore them, but to be cautious and look for additional signs that it isn’t just passive noise. If it IS stability-related it generally looks smoother and broader, not like this. You can also create the Bode plot from these two traces, since BODE=1-OFF/ON. This is from small signal theory closed loop=open loop/(1-T) and solving for T, where closed loop is ON and open loop is OFF. I have a few papers on this, but see attached. We do have one customer that insists on 1600 datapoints, so there isn’t really a guide, but for mine I usually like to see 20points/decade UNLESS I am looking at a sharp peak. For example, xtal is very high Q, so needs a lot of datapoints for good definition. The series resonance of a ceramic cap also might require more points to accurately produce the sharp impedance dip. One more tip is to use LOG magnitude for the Qtg curve (and the impedance curve) and it won't get as “blown out.” Steve

Thanks for this question, it is a good one, and probably of general interest. I looked at your settings, and you did all the right things to manage noise. Which is great. There are few things to be aware of here. First, the best method for this impedance measurement, voltage permitting is the 2-port shunt through. That is the lowest noise and is optimum for measuring very low impedance. NISM uses Qtg, which is a derivative, making it very susceptible to noise, but this is generally overcome by good noise management technique, which you have applied well here. This is not about the magnitude of the impedance, but about the Q. 1. The measurement itself is very low Q, so we don’t actually expect to see a peak, and the NISM would generally report >71 degrees. Pat yourself on the back, this is a keeper. It is also generally recommended that you measure with power both OFF and ON, again making the 2-port shunt through measurement ideal. This will clearly show where the ON impedance is greater than the OFF impedance, and that is the peak we want to measure. 2. You do have a very sharp peak at around 10kHz. This could be noise from your board, noise from external sources (we have seen LED lamps, monitors, etc. create such noise) and it can also be control loop related. Measuring with power OFF and ON would help determine that. 3. You could use the traditional 3dB cursors (Bode 100 offers these) to determine the Q, which looks to be below 0.5. This is a very stable loop, and that is why you are having trouble finding the peak – there isn’t one!! If you see this situation generally, congratulations, you are doing well. If you perform a step load on this VRM you will also note that there is no ringing, since this is overdamped. Well done! Steve

Yes, NISM does work for COT converters, where Bode plots don’t. MPS suggests using step load instead. Step load measures the same thing as NISM (output impedance) but with much higher fidelity and a transform back to stability margin. Please let us know if there are any follow up questions. Thank you!

This is the DC cable that shipped with the J2111A and J2170A. Yes, you can order a replacement. The connector is from Kycon, but hard to find. We do have some cables in stock. Please click here to order. Let us know if any additional questions.

The MSO6B with the latest power software is capable of both 2 port (VNA) and three port (FRA) frequency domain measurements, though the FRA doesn’t provide impedance units (yet). You don’t say what your battery voltage is, but for low voltage batteries, the 2-port shunt through is more accurate, though requires an attenuation resistor, attenuating probe, such as P2102A or DC Blocks. The measurement also requires the J2162A active splitter and either J2102B coaxial transformer or J2113A active splitter to measure low impedance at frequency below about 1MHz, depending on the cables. The FRA method requires the J2111A, which includes a 1Ohm current monitor, and with a low noise scope probe, can also measure impedance. While we don’t usually discuss it, there is also a similar ground loop in this measurement, and in fact, in most measurements. Since this measurement is a current sink, it’s a floating measurement. Either of these measurement techniques can measure 1mOhm or lower with care. I attached a verification of the J2111A impedance measurement, performed by Keysight, using their E5061B VNA. This VNA has an advantage in this it has a differential input for the voltage measurement, eliminating the ground loop. A standard differential probe is generally pretty noisy, so not quite as good for low impedance measurement. Using a J2113A or J2102B with one of our P2104A or P2105A probes or will yield the best results if the impedance is very low. We have most of these in the demo pool, if you would like to borrow one. We can use the measurements to create an application note for the MSO6B. Email info@picotest.com for any demo equipment requests.

There are many ways to mount a PCB to the holder http://www.clampman.info/ft_downloads/clampman/clamping_methods/clamping_methods.png Inside the arms, a PCB of about 10” x 15” fits. Sliding the ends over as in the picture below, the length isn’t limited, if the PCB is seated in the groove. If the PCB isn’t in the groove you can use the slots, screws or know grooves to hold the PCB and then it will depend on where holes are available on the PCB. The weight limit is about 5lbs for a normal permanent load in an almost upright position. Above that the hydraulics get stress and can even drain. Hopefully this provides guidance but if the customer has a specific PCB side / hole locations, I am happy to see if it would fit, since I have this same model myself.

0603 is in mils. The first numbers (06) is the length and means 60 mils and the second two (30) are the width and mean 30 mils. So an 0603 component is a MAXIMUM of 60 mils x 30 mils. If you wanted to measure on a component, you would want a 50 mil pitch and if you wanted to measure on the pads, you could probably use 40, 50 or 60 mil pitch. Ideal would still be 50 mils so that the ports are in the same place on the component as they attach on the printed circuit board. So for 0603 I would likely choose a 50 mil probe pitch.

Thanks for the comment. These probes are designed for a specific purpose. We can't accommodate every pattern, but what we do is mount larger components with connectors and all probe pads on the back side. If you are asking to be able to solder leads to the probe, we could possibly accommodate that. We did have socket pins in the earlier P2101A version, which can't get to milliohm, but does have socket pins. The majority of requests were for a more accurate, higher bandwidth 4 point Kelvin probe and this version has already outsold the P2101A. We do want our customers to succeed and are happy to help. Click here to email Steve Sandler and we'll see if we can come up with a solution for you, possibly using a custom tip. FYI, we do regularly make custom tips for this probe and most requests have been for smaller pitch, not larger pitch.

We don't currently make a differential TDR probe, though hopefully one will be released in 2022. A pair of P2105A's will work and are well-matched. We can match to within about 2ps, but they are typically within about 2ps anyway. P2105A product page: https://www.picotest.com/products_P2105A.html

Thanks for posting, Brad! This user manual may also be helpful: https://www.omicron-lab.com/fileadmin/assets/Bode_100/Accessories/B-AMP_12/B-AMP12-UserManual-ENU11880503.pdf

PDN Cable is ideal, since it has lowest shield attenuation and also shield resistance. RG58 or equivalent isn't quite as good, but it's inexpensive and readily. Keep it short and that will help minimize the impact. The bigger issue with the inexpensive cables is that the crimps aren't usually very good. The 1Nm is the recommendation of our connector manufacturer. I generally use 0.4Nm since I have that wrench already. You'll notice in my demos I generally don't use the wrench so I can change connections quickly. At these low ish frequencies it has little impact. In the SI world it is much more critical, since a loose connector can exhibit some excess inductance. I showed that in my Power Integrity book. Some helpful links: https://www.signalintegrityjournal.com/blogs/8-for-good-measure/post/1441-what-makes-pdn-cable-special https://www.picotest.com/blog/why-specialized-pdn-cable-is-essential-for-your-power-integrity-impedance-testing/

Great question. It is possible to measure this filter. You are correct that it would short through the BNC's using a traditional setup. You have a few options. 1) Use current, rather than voltage injection. For example, with a voltage source at the input and modulate current at the filter output. Measure the current at the output current divided by the input current. This will provide the transfer function. Our J2111A can create the current injection and provide a current monitor. Any current probe can measure the input current. Be sure to calibrate the measurement by placing the current probe on the J2111A lead and performing a THROUGH calibration. A Rogowski probe won't add any insertion impedance. See our PEM Rogowski probe. You could also connect the Bode 100 output to the filter output. Then use a current probe on the OUTPUT lead and a second current probe in the shorted INPUT lead. 2) Use differential probes to measure the input and output. You want low noise diff probes. We have one coming later this year. It will be our P2103A. 3) Add an isolation transformer or coaxial transformer at the filter output. The isolation impedance needs to be greater than the return side filter impedance (J2102B or J2113A might work).

I haven’t ever derived or really discussed the equation, though I have shown it and discussed the method frequently. If you look at this 70GHz image, taken by Mike Martin for us, you can see the perfect edge of our J2151A TDR. We even trademarked PerfectPulse. The other 2 images show the dVdt of the edge. This is a bandwidth limited impulse. The bandwidth is 0.35/edge speed. Looking at the FFT of an impulse it is flat response up to this bandwidth. You can see that in the FFT. This is of course only looking at the 1 channel that is the generator. Through probes, cables, etc, this edge can be degraded, but we can measure what is at this “port”. If I connected this to a second channel through a perfect cable, the second channel would see the same thing as the first and dividing them would provide the transfer function. If we present the signal to the DUT through 50 Ohms (our TDR splitter does) we’ll measure the S-parameter, S21. The second channel also looks at the derivative, since it is also a response of the signal comb, though the scope connects these points with smoothing for us. This is a division, but since the measurements are in dB we subtract these to get the division. This is a neat trick. We can use this to measure uWave frequency response. I attached a few measurements using this “VNA”. You’ll see 1.57GHz and 4GHz bandpass filters and also a 20dB attenuator for verification of the math. If we turn the splitter around so we DON’T present 50 Ohms, we can also measure the transfer function of probes, cables, etc without the 50 Ohm damping. See the attached PML probe measurement and the Tek005 (power rail probe). Of course this also works to measure the scope transfer function and the bandwidth limiters and the step vs flat response selections, etc. It’s quite a handy tool that fits in your pocket. We do have setup files for all of these, since we showed them in our Tektronix events. FYI, this is also how the calibration labs validate our 10.5GHz specification for our TDR. Using the same method as I showed here. It just requires a scope with much more bandwidth than our 10.5GHz edge. Using the signal generator for TDR, just looks at the same signal, but a bit differently, evaluating mostly the reflections. One more highlight. Looking at the attached Tek003_001, you can see ringing on the edges. Both edges. Interestingly, you can also see the ringing BEFORE the transition from low to hi and hi to low. Hmmm, that says there is a pre-response or a non-causal response. How can that be? That is a perfect picture of the Gibbs phenomenon 😉 So much fun in one pocket sized gadget… Also see this helpful article Measuring a Scope Probe Requires Two Oscilloscope Channels and a Very Flat Signal Source

Steve: This is a good question, and I think I mentioned it in one of the videos. If you want the ENOB and dynamic range of the scope remove them, if you want to know the ENOB and dynamic range of the measurement everything should be connected. Attendee: Also, what was the measurement for the Tektronix scope noise (shown in the lesson) (at 50ohm,1 Meg, at 2mV /div and 200mV/ div also with and without averaging) done with probes or without them? Steve: I don't recall, though it should be shown in the slides and demo and the setup file is in the Links and Downloads area. As I showed this is also dependent on the probes and cables as well as the ambient lab noise. For example, I showed my wifi and even LED photo lamps getting into the measurements. Having said that, MSO 5/6 are among the lowest noise scopes we've used here.

The J2120A is a passive device and yes, it can provide a 1.2V output. The graph below is from the J2120A webpage showing the operating current dependent voltage drop and output resistance. Since the regulation requirement for your 1.2V is probably tight, I would see the attached application note for remote sensing the J2120A. Of course the remote sense is quite slow, so that it doesn’t regulate out the modulation signal. Not every power supply has the compliance needed (up to about 3V), but the Picotest P9610A does. You will still want to avoid fast load changes so that you don’t see large transients on the 1.2V J2120A output.

See the Keysight videos here https://www.youtube.com/results?search_query=How+to+Design+for+Power+Integrity%3A