I might also have been lucky in getting two LMH6702s with the same gain and DC offsets, if I get two that have individual differences that could introduce DC offsets or gain errors in the output. When it comes to the LT1364, I knew it would not be fast enough. Most 1:1 (Isolation) transformers pass the Earth GND pin through the isolation barrier. You previously purchased this product. Yes. I am planning to buy Rigol MSO5204 scope with a bandwidth of 200 MHz. One for 6000V will be very different from one to look at 10 mV in 10V. Other than that Im thinking about building an USB powered DC-DC converter to make the probe easier to use. Differential Oscilloscope Probe 10:1 50MHz 70V : Amazon.co.uk: Business, Industry & Science You can think of this circuit has having three sections: an attenuator, a buffer stage and a difference amplifier stage. 19% VAT R&S RT-ZHD60 Leading Designer and Supplier of Tablet Portable Oscilloscope & Oscilloscope Probes | Micsig is a professional supplier of digital oscilloscope, leading in tablet portable solutions in the field of Test & Measurement. +/-3V at the inputs (X axis) become a +/-300mV signal at the scope (VM3). If you try to measure a device that has a ground which is at 50V relative to the probe and scope ground you will most probably fry the OP-AMPs on the probe. Attenuation factor of 1:1 means whatever signal being probe at the probe tip will be shown exactly as it is at the oscilloscope input. Bestest option is fully-isolated diff probe someone else bought you :D. maybe a solution can be found where (as in some analog input stages) AC and low frequency / DC content are transfered separately across the barrier (DC transfer via a closed-loop solution, AC magnetically coupled)? I assume 220 ohm was chosen because it was more convenient somehow (probably on stock). However much you might wish for an oscilloscope with electrically isolated inputs, it's hard to justify the cost for personal projects. A guard ring would reduce the input capacitance (effects). Requires. I found the LTC6269-10 through a paper titled, "LTC6268-10 Oscilloscope Differential Probe." The circuit was AC-coupled and had a very small common-mode range, but the amplifier was pretty amazing: 4GHz GBW 0.7mV input offset voltage @ 25C. Differential Probes 60 V Common Mode The ideal probes for lower voltage GaN power conversion measurement with the highest accuracy, best CMRR, and lowest noise. Why? are any of these a suitable substitute for the discontinued BF998 mosFET? Review request: DIY DC to 50MHz differential oscilloscope probe, Stop requiring only one assertion per unit test: Multiple assertions are fine, Going from engineer to entrepreneur takes more than just good code (Ep. +Input 10 M It might not make any difference though, the PSRR of the LMH6702 is 52dB typical and the CMRR is 48dB typical. . AC performance looks decent. Some models are . Now the offset is a smaller, but still significant +30mV. [Christer Weinigel] needed to get some measurements of a differential clock signal that was ticking away around 500 MHz. Maybe I should submit and buy components online, but then I'd have to wait and pay postage fees. Their disadvantage is that some sort of high impedance buffer will be required for each input. This site uses Akismet to reduce spam. . If you want to know how to make a basic oscilloscope, then this design will be of immense help. The last screenshot is the SMA connector being probed directly by another 1:10 passive probe. :-). simulate this circuit Schematic created using CircuitLab. You dont have enough supply voltage on this chip to get 1kV/us so you only have 385V/us and thus bandwidth limited for large swing, Datasheet says =+/-5V full power BW= 3V Peak, (Note 6) 5V only 23.9 MHz, so that is a No Go. I dug a bit deeper about that stability that you mentioned. Name for phenomenon in which attempting to solve a problem locally can seemingly fail because they absorb the problem from elsewhere? DIY Radio Electronic Kit STC89C52 87-108MHZ W/ For Soldering Learning Teaching! At higher frequencies its the 150Ohm input resistor together with the 1.6pF non-inverting input capacitance (and any parasitics) that will dominate. Those probes are quite expensive. journeymanwizard, I think you misunderstand. Differential probes would be widely used were it not for the price. Scope makers just don't see a need for this analog stuff today. With higher frequencies like this, its going to be demanding on the op-amp, so [Christer] spent some time simulating the circuit to make sure it would work with his chosen part. C $499.98. These probes are not compatible with Keysight's InfiniiVision 1000 and 2000 X-Series oscilloscopes. Pintek DP-15K 35MHz, 15kV differential probe input stage uses two THS4631 with another op-amp and DC servo. The last screenshot is the SMA connector being probed directly by another 1:10 passive probe. CT2593-2. Will it have a bad influence on getting a student visa? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. This one has the higher BW. 4210-1 9 Volt Regulated European Adapter Use with 4222,4231,4232,4233,4234,4236,4236, 4241 & 4241A Differential Probes Length- 64" Output- 9Volts DC, .065 AMPS Input- 100 VAC to 240 VAC Will work with all differential. The transformer is a $5 item and the frequency response was quite flat from 30Hz to about 200kHz. The scope is a 50 MHz Rigol DS1052E, with 1M 15pF inputs. mihai.cuciuc liked Loko-the Tiniest GPS tracker with 270 days battery. That circuit looks significantly simpler than Idve imagined. Then it could measure circuits without loading it too much. The S/N ratio also needs to be good too, for QLN measurements. You need the 220 ohm in order to be stable. El-cheapo probes arent going to cut it here. It can be used to measure a differential signal such as a LVDS clock, but it can also be used to measure a single ended signal relative to a nearby ground pad. VM3 measures the signal at the scope input. Even the "low-bandwidth" probes were still around 1GHz of bandwidth. The WiFiScope WS4 DIFF is a powerful computer controlled battery powered WiFi oscilloscope that features four built-in differential input channels.. I really should write another post on why I think the probe works as well as it does. For Tektronix Oscilloscope Probe 3.5/4.3/4.5mm Ground Spring Torsion Spring Kits. A few selectable input voltage ranges, from 3V pk-pk to 300 V pk-pk, Better than 1/500 common mode rejection ratio, Realizable with the limited selection of parts from my local electronics store. Consider a better design. Video showing a few of the the basics of building a home made high voltage differential oscilloscope probe. ^^ pretty good then. 1. In many ways I think I lucked out on the component selection. 1:1 active differential probe (over) 100MHz of bandwith 100k input resistance max 700Vpp or 2500Vpp (depending on C1,C2) Electronics As explained above, the heart of the circuit is based on two Linear Technology LT6268-10 high-frequency amplifiers, IC1/IC2, to obtain a fully differential oscilloscope probe with interesting specifications. is asking for a review of. [Christer] needed the difference between two balanced signals, neither of which is grounded. Shorting Pins for storage? To add to the comments about other amplifiers (not saying you should change the design, just that it may be of interest! A differential probe is an active device which uses a differential amplifier to measure the difference between two signals. Anyway, again: I built up a few. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. The Tektronix THS700 does almost exactly what you describe for its isolated scope inputs. Right now I need to power the probe from a power supply which can deliver +/-5V which is a bit cumbersome. The average oscilloscope probe has a bandwidth of less than 300MHz. $699 Add to Cart MSO8000-JITTER Jitter and Real-Time Eye Diagram Analysis Option $999 Add to Cart PA1011 10W POWER AMPLIFIER FOR GENERATORS. You are using an out of date browser. Edit: By total coincidence, Bil Herd just posted a video intro to differential signals. Do you think the BAS diodes will be fast enough to protect the FETs from ESD with direct connection? The writeup goes into some detail about how he was varying R1 and R4 to compensate ringing. Minimizing the loop area between the signal and nearby ground pad minimizes the noise picked up through that loop. The schematic and a PC layout are attached to that first post. Active Probes & Differential Probes. 2. It wasn't necessary, so I didn't try. ), I seem to recall that the EEVBlog 70MHz diff probe uses both an AD8130 and an AD8129 - I assume with both always connected and the outputs muxed via the shutdown function. The best answers are voted up and rise to the top, Not the answer you're looking for? Any noise coupled through the ground wires, which changes the common mode, will probably make a bigger difference than noise on the power supply. Editor's Note: This article on current measurement and current probes is the third of a three-part series on probes and their proper use.Part 1, covered high-impedance passive probes.The second article discussed single-ended, differential, and high-voltage differential active probes. An almost-GHz active differential oscilloscope probe. The JFET buffer stage has a higher bandwidth than what my scope can measure, I don't see a problem with it. David Matthew Mooney has updated details to The Learner's Heliostat. Oscilloscope Probes. Useful especially if one is designing or fixing switching power supplies. I remember in '80's lots of young EE's blowing the front end FETs on Tek FET buffered Diff Probes that blew with 25V. Not great performance. For the simplest design, a high input impedance instrumentation amplifier like you selected will work but also consider using a current feedback "difference amplifier" like the AD8129 or AD8130. Even a SMA connector has a capacitance on the order of a dozen fF or 33kOhms of reactance at 400MHz. Fancy measurement gear is often expensive to buy, but some bits of kit are entirely DIYable if youre willing to put a little work into the project. A red LED performs the dual function of indicating that the probe is on, and providing a ~1.8 V bias voltage for the current sources. My profession is written "Unemployed" on my passport. The commercially available probes do not fulfill the mix of real life situations: for DSL measurements, you need 25Vpp signal handling capability, 70V common mode and a minimum 30MHz bandwidth. That looks like there will be no output from this circuit. I remember decades ago struggling with 1ns rise time clocks for a Doppler Application when I should have known about CML logic and solved it easily. The signal attenuation can be adjusted in two levels : X20 and X500. In the UK I tend to use RS for free next day delivery. Why was video, audio and picture compression the poorest when storage space was the costliest? 3. 1.5pF input capacitance 800 MHz GBW, PSRR >50dB, then R ladder network divider. Bandwidth of an oscilloscope with differential probe. Reduce frequency to 1 or 2 Hz. JavaScript is disabled. Fine for AC though. Anyway, I fully understand the too much to do, too little time ;), [1] http://www.sersc.org/journals/IJCA/vol7_no8/15.pdf, Regarding the active shield. I showed stock of my solution which I believe is in your location. Ive read things in the past about using active shielding or something like that; the output of the opamp is circling the negative input pin of the opamp to reduce effects of capacitance to ground. The Sapphire probes (the 9001 version) use 4 Meg and 26K dividers, resulting in a 0.65 attenuation factor, and this result gets amplified later on. Does the LT1364 normally get warm when it is in circuit? :-). You probably already know that most scopes can use 2 probes and channels to produce a differential signal. The internal circuits inside the probe tend . You need R5/R6 for stability. But yes, the resistive divider would make sure that most signals Id want to measure are small signals. Passive Probes The QA400 is an audio analyzer that did not have a differential input. Keysight offers a wide array of Probes and Probe accessories for your specific testing application. @jms depending on where you are there are fast and/or cheap online delivery services. Jakob Flierl has added gutu.ashe as a contributor to HB100 Radar Shield. If you tried to buy one of these, itd set you back the cost of a few hundred lattes, but this one can be made for the price of one or two if you get the PCBs done cheaply. Jakob Flierl has added roshanka32 as a contributor to HB100 Radar Shield. Future revisions should have a mechanism for compensating for this offset voltage with a trimmer pot. Another thing Im thinking about would be to use a SATA or E-SATA cable to connect to the probe instead of using a MCX or SMA connector and a separate connector for the power supply. This is the equivalent of a passive 1x oscilloscope probe, which still may be too high of a load on the DUT and could even influence the operation of the DUT, causing measurement errors. Measuring the difference between the single ended signal and the nearby ground pad lets the instrumentation amplifier cancel out some of the noise picked up through the longer ground path from the probe ground to the device ground. August 25, 2021 by Dave Rowntree 14 Comments. Active probes have opposite characteristics to the rugged passive probes. As can be seen, terminating both ends results in a clean signal without overshoot, but with only roughly 13 MHz of bandwidth. Your idea of reducing the input voltage divider by a datasheet would increase the maximum bandwidth of your opamp (check your datasheet); reducing the input voltage to 0.5 Vpp would increase the bandwidth to 1700 MHz. I need to measure the timing difference between 2 (or more) signals of up to +/- 7 ns. And the product is a probe type, oscilloscope and probe, which can meet your different needs. In the first four screenshots the yellow trace is the output of the DIY differential probe, multiplied by 10 by the scope, as connected in the diagram. Then go to the math function and enable CH1-CH2 which means a difference. 50 ohm impedance matching is already provided by R11. Digital Logic Probes & Cables. *tries to remember how to calculate reactance* *fails* *googles* X=1/(2*PI*f*C). Since I dont have any control over stray capacitance just mounting the LMH6702s slightly differently might change it. Micsig Technology | 165 followers on LinkedIn. (See this article on in-amps if you need to brush up.) rev2022.11.7.43014. It delivers solid performance and a variety of basic and enhanced capabilities in a compact 2U package. You probably already know that most scopes can use 2 probes and channels to produce a differential signal. Add . The first two OP-amps are used as high impedance buffers. Learn how your comment data is processed. Find many great new & used options and get the best deals for Tektronix Oscilloscope P7330 3.5G High Performance Differential Probe (R3) at the best online prices at eBay! Daniel Kramnik built an active differential probe and looks like he is seeing about 400MHz usable bandwidth. ", Find a completion of the following spaces, Space - falling faster than light? Digital Logic Probes & Cables. I had no problems relating to the layout itself, but I absolutely should have designed the board with mounting to a shielded case in mind. Part 3 will deal with current measurement and current probes.. The amplifier front-end is realized with JFET source followers in order to provide a high impedance to the attenuator stage. Common Mode Range > 340V (240VAC produces a sine wave 679V peak-peak) Are the BJT current sources fast enough to sink a constant 5 mA given a high amplitude (3 V pk-pk at JFET gate) 50 MHz signal? Making statements based on opinion; back them up with references or personal experience. apply to documents without the need to be rewritten? WiFiScope WS4 DIFF. Im planning to do a blog post about that but I Id like to check the frequency response of the SATA thingy on a network analyzer before I blog about it. Be aware that this information is not stated anywhere! Illustrated below is a 1:10 attenuator (roughly +/- 30 V range). If HV means high voltage, my goal was _not_ to make it a high voltage probe, my goal was to make a low voltage probe with as much bandwidth as possible while keeping the input impedance as high as possible. The Diodes must conduct faster than the FETs to protect them and ESD can be 10's of amps for picoseconds. Active 1.5 GHz differential probe with button for device control, integrated R&S ProbeMeter for accurate DC voltage measurements and R&S probe interface. Actual results matched fairly well with the simulation. I have since tried a few other OP-AMPs and they did not work as well the LMH6702, they either have too much bandwith which gives much peaking and makes the probe unstable or have too low bandwith which gives a much lower total bandwidth and I havent been able to compensate for that with a different input resistor. This is a realistic alternative but it may be problematic. I'll open the box and sh. Active Probe Setup (via xellers) Back when I worked for an Oscilloscope company, we were pretty proud of our differential probes. When I first built the probe, it output +600 mV with the probes shorted together. This pc oscilloscope has some excellent features like an auto-trigger, a frequency counter, a 50k sample/seconds, and a selectable voltage range - 5V, 6.6 V, 10 V, and 20 V. To make this DIY oscilloscope, you . Shipping costs outside EU in 11-21 days in stock. Tektronix offers TriMode architecture which streamlines measurement acquisition by enabling you to make differential, single-ended, and common mode measurements with a single connection! Oops. An oscilloscope probe is a device used to connect a signal source, often a test point in a circuit, to an oscilloscope; a physical connection making the electrical connection. This topology was selected in order to circumvent the relatively high input bias current (worst case 2A) of the available op amp. What is this political cartoon by Bob Moran titled "Amnesty" about? Our Probe accessories offer extremely low input capacitance, flat frequency response and superior signal fidelity. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. 20 channel differential Multiplexer module for use. 5,700.- net ( VAT Details) 6,783.- incl. You want to minimize drift due to the trimpots because of the high attenuation ratio in the voltage divider. Differential probes are especially popular for measuring high-frequency signals or signals of very low amplitude (i.e., approaching the noise floor). Free delivery on eligible orders. Standard and high-sensitivity solder-in, HiTemp, and QuickLink for mixed-signal probing. You probably already know that most scopes can use 2 probes and channels to produce a differential signal. Differential Probes and accessories. So, starting from the top, R13 and R24 are drain resistors that set the gain of our differential stage. Why does R12 exist? No, R1/R2 are not part of the probe, they are meant to represent a differential termination that Im doing measurements on. Choosing the Right Pico Technology Active Differential Probe If I assume that the total capacitance is about 1pF this filter would have a bandwidth of about 1GHz. Yes, the resistor value used is just because 220Ohm is a common value for resistors (E12 series) and 237Ohm is not. Please be kind and respectful to help make the comments section excellent. There are three common techniques for . So as a handy trick, make 2 anti-parallel led's as each load. Home; Test, Measure & Inspect; Electrical Testing; SKU:IN6297824. mime, my probe does have a >500kOhm input impedance, at least at DC. 2. Even differential probes, which (within certain limits) enable voltages to be measured without reference to ground, often cost the private user more than a complete scope does. They have an input resistance of 100kOhms or so at DC and 0.3pF of capacitance which would mean about 1.3kOhm reactance at 400MHz. Does it ever make sense to use a 50 input with 10X scope probe? The schematic and a PC layout are attached to that first post. Find many great new & used options and get the best deals for 10M Bandwidth Oscilloscope Differential Probe Gain Split Probe Signal Ampli L4U3 at the best online prices at eBay! (In this case, the input capacitance of the opamp is similar to stray capacitance on the inverting input.) :-) Adding a parallel capacitor to the input resistor sounds like a bad idea, it would reduce the input impedance and increase loading. View in Order History. I can finally answer my own question in hindsight. This probe is limited by the supply voltage to the OP-AMP anyway, so it wont work with anything much beyond +/-3V or so. Current Probes. Yes, the small signal response of the LMH6702 is supposed to be faster than the large signal response. New. $22.67. But learning is good. Also, a cheaper model in the line Rigol MSO5074 offers . I was trying to model the effect of parasitic capacitance by adding capacitors to ground in a lot of places and when I cleaned up the schematics I messed up and shorted the output to ground instead of removing the ground as I should have. The nomal ones cost a fortune because they are not referenced to earth. For power engineers who work for mid-sized companies, there is only one path: build your own probes. Free shipping for many products! DC (CH1SLO) is passed over the isolation barrier with an optocoupler. If you try to measure a device that has a ground which is at 50V relative to the probe and scope ground you will most probably fry the OP-AMPs on the probe. Adding a voltage divider at the input would lower the impedance which defeats the purpose of the buffers. https://en.elektronicastynus.be/2009/06/01/differential-probe/4. (Comment Policy). Differential probes are oscilloscope probes designed to measure the difference between two signals. It only takes a minute to sign up. Make sure that both vertical amps are set the same. Best to use resistors and then the smallest trimpot value. 8.04 From RS Electronics, Specs: 1.5pF input capacitance 800 MHz GBW, PSRR >50dB. DC performance in simulation looks good. Now, because JFETs usually have a very low transconductance, that means that the gain will be relatively small. A simulator makes it easy but real hardware needs real oscilloscopes. cant you just run it off a bench dc supply with out the earth tie on the neg? E. recipe for an audio range (5-50Khz, or at least 20-20KHz) with good sensitivity down to ~10uV per unit. By using our website and services, you expressly agree to the placement of our performance, functionality and advertising cookies. In this way, an active probe with 2.5-V dynamic range can read zero to 5 Vdc.
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