500uV/Div Oscilloscopes - Page 1
Forum section: electronics / beginners

author: Jon_Paul_Clarke
author_rank: Contributor
timestamp: June 16, 2014, 08:07:20 am
content: Evening all,I've been trying to look for other models of CRO that have the golden "500uV/div" sensitivity for the channel inputs, but I have only gleaned a few model numbers from Dave's video rants/CRO p0rn/Interweb debates. They are:1. The venerable Tektronix 22252. The Hybrid beasty Tektronix 22113. Possibly the 2214?4. The sexy Tektronix 24405. The Tektronix 7000 series (with appropriate plug-ins)6. The rock solid Hitachi V-1050F7. Others?...This is about as many as I could get, does anyone else no of other Models/Makes that have this input sensitivity?Also, I'm trying to get my hands on a 100MHz model for all-round work. I know that there are many DSO's out there that would meet these criteria but I would like something Analogue to cut my teeth on.Thanks in advanceJon

author: robrenz
author_rank: Super Contributor
timestamp: June 16, 2014, 10:22:46 am
content: Tek 5000 series with appropriate plugin

author: Jon_Paul_Clarke
author_rank: Contributor
timestamp: June 16, 2014, 11:00:12 am
content: Ah, right. Of course. I forgot about the 5000 series.Thanks robrenz.

author: plesa
author_rank: Frequent Contributor
timestamp: June 16, 2014, 11:23:48 am
content: What about LeCroy DA1855A ?

author: lapm
author_rank: Frequent Contributor
timestamp: June 16, 2014, 11:31:57 am
content: Sounds like someone needs to build small box to boost signals in front of oscilloscope... I wonder how terrible demanding that would be considering bandwidth requirements and signal intergity...

author: robrenz
author_rank: Super Contributor
timestamp: June 16, 2014, 11:57:29 am
content: To be done well is not cheap as evidencedhere at about $2600.00

author: EEVblog
author_rank: Unknown
timestamp: June 16, 2014, 12:00:37 pm
content: Quote from: lapm on June 16, 2014, 11:31:57 amThis has been one of my to-do project for a long time.Last I had a brief look at it, I think 20MHz (typical test gear noise measurement bandwidth) was quite doable for x10That would give any scope at least 500uV/DIV, most 100uV/DIV

author: Jon_Paul_Clarke
author_rank: Contributor
timestamp: June 16, 2014, 12:08:52 pm
content: Good point about the sensitivity boost before the front end via probe or black box contraption. I overlooked that because I thought that it was "cheating". I guess there's no such thing in electronics as long as it's soldered/crimped properly. Eh, Dave?

author: Jon_Paul_Clarke
author_rank: Contributor
timestamp: June 16, 2014, 12:10:58 pm
content: LeCroy DA1855A, you say? Thanks. I'll go and google that now.

author: robrenz
author_rank: Super Contributor
timestamp: June 16, 2014, 12:34:00 pm
content: Very versatile bit of kit but only 10X gain yet good for very high voltage with proper probes and the XC100 10X/100X box. has built in precision DC offset. Usually around $900.00 but I snagged this one with a $300.00 offer long ago.

author: plesa
author_rank: Frequent Contributor
timestamp: June 16, 2014, 01:23:38 pm
content: Quote from: robrenz on June 16, 2014, 12:34:00 pmWould you mind to do teardown of 1855?

author: robrenz
author_rank: Super Contributor
timestamp: June 16, 2014, 01:45:00 pm
content: I am not really qualified to do a worthwhile teardown :-[and this has some very high impedance stuff inside so I feel safer leaving alone.Just like I am not teardown of my 2450SMU anytime soon either, I just don't trust myself to not do something stupid in the process.

author: jlmoon
author_rank: Unknown
timestamp: June 16, 2014, 05:57:01 pm
content: Quote from: robrenz on June 16, 2014, 12:34:00 pmThats a LeCroy jDA1855A diff amp with a new wrapper....

author: robrenz
author_rank: Super Contributor
timestamp: June 16, 2014, 06:11:28 pm
content: Actually an OLD wrapper, Lecroy bought Preamble.

author: jlmoon
author_rank: Unknown
timestamp: June 16, 2014, 08:05:33 pm
content: ah, learn something new everyday! They sure are proud of those devices..

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 16, 2014, 08:26:59 pm
content: Hi,I would add the Tektronix AM502 in a suitable mainframe TM501- TM506 to the list of pre-amplifiers to consider.This is a differential amplifier with The gain can be set from 1 to 100,000 in the 1,2, 5 sequenceIt has two filters the HF corner can be set from 100 Hz to 1 MHz, 9 steps in 1-3 sequence.The LF corner can be set from 0.1 Hz to 10 kHz, 6 steps in 1-10 sequence.Limiting the bandwidth can sometimes help dig a signal out of the noise floor.This is very similar to the 5A22 and 7A22 oscilloscope plugins.The AM502/TM50x mainframe can be used to increase the sensitivity of any oscilloscope.Link:http://www.barrytech.com/tektronix/tektm500/tekam502.htmlRegards,Jay_Diddy_B

author: Dave Turner
author_rank: Frequent Contributor
timestamp: June 16, 2014, 10:47:49 pm
content: DaveHow about it - design a 500mv/division or better amplifying probe combined with a differential probe; all switchable of course? It's sort of similar to the microamp.It's way past my ability but just possibly could bridge a gap between reasonable and out of reach epuipment for the majority.

author: Electro Fan
author_rank: Super Contributor
timestamp: June 17, 2014, 03:26:48 am
content: Quote from: Jon_Paul_Clarke on June 16, 2014, 08:07:20 amAny idea why Tektronix only offered 500uV/Div on these relatively few models, and why they picked these particular models vs. others?

author: rf-loop
author_rank: Super Contributor
timestamp: June 17, 2014, 05:30:38 am
content: This is not exactly what asked but still handy in some cases.Tektronix all 24xx (and some other old models) analog scopes have CH2 signal output (rear panel).20mV/div to 1Mohm and 10mV/div to 50ohm.CH1 and CH2 can use cascaded.Connect signal under test to CH2 input. (you can even shut off CH2 if no need watch directly, signal is still routed to its output.)Connect CH2 output to CH1 input. Set trigger source to CH1.For 1mV/div and 500uV/div:Set CH2 for 5mV/div and CH2 output to CH1 inputSet CH1 for 2mV/divNow signal (true input is CH2) is 1mV/div on the screen if CH1 impedance was set for 50ohm (better response) or 500uV/div if CH1 input is set for 1Mohm.For 400uV/div and 200uV/div:Set CH2 for 2mV/div and CH2 output to CH1 input.Set CH1 for 2mV/divNow signal (true input is CH2) is 400uV/div on the screen if CH1 impedance was set for 50ohm (better response) or 200uV/div if CH1 input is set for 1Mohm.Of course oscilloscope cursors show values related to CH1 settings and user need think right level.Not perfect and also frequency response is some amount reduced (cascaded CH1 2mV and CH2 2mV response and if not 50ohm then also this impedance mismatch (cable lenght etc)In some cases this is still useful.

author: plesa
author_rank: Frequent Contributor
timestamp: June 21, 2014, 07:36:09 pm
content: Quote from: robrenz on June 16, 2014, 01:45:00 pmI understand. Few internal pictures will be appreciated,I'm just currious. About teardown of SMU, don't afraid, if you are removing covers it is OK. I make this type of teardown on my 2636B and several picoammeters which I need to repair.I hope Dave will make the teardown of the Agilent SMU sooner or later.

author: David Hess
author_rank: Super Contributor
timestamp: June 22, 2014, 06:35:14 pm
content: Quote from: Electro Fan on June 17, 2014, 03:26:48 amThere were at least two different series within the 22xx line and the 2201, 2205, 2210, 2211, 2214, and 2225 formed one of them with 25pF inputs and 20 MHz or 50 MHz input bandwidths. Of those the later 4 included x10 vertical magnification which served double duty as a 5 MHz bandwidth limit that could be applied to individual channels instead of all of them together.The other 22xx oscilloscopes had 20pF inputs and 60 MHz or 100 MHz bandwidths.

author: David Hess
author_rank: Super Contributor
timestamp: June 22, 2014, 06:59:19 pm
content: I am really only familiar with the Tektronix products so I will just list the ones that come to mind:The 2225 sub-series within the 22xx series oscilloscopes which includes the 2210, 2211, 2214, and 2225 all have x10 vertical magnification which also serves as a 5 MHz bandwidth limit. The 2225 is analog only but the other three combine analog operation and digital storage.The 7A15A (but not the 7A15!) single channel 80 MHz vertical amplifier plug-in for the 7000 series mainframes has x10 vertical magnification which also limits the bandwidth to 10 MHz.The 7A22 differential 1 MHz vertical amplifier plug-in for the 7000 series.The AM502 differential 1 MHz amplifier for the TM500 series test instruments duplicates the capabilities of the 7A22 for any oscilloscope.Various 5000 series vertical plug-ins.The vertical output on 7000 mainframes provides a roughly calibrated 25mV/div signal and may be used to cascade vertical amplifiers for increases sensitivity however noise may be a problem. There are other oscilloscopes which can do this as well.Honorable mentions should go to the 2216 which is a 4 channel 60 MHz (10 MHz at 1mV/div and 2mV/div) combination analog and digital storage oscilloscope and supports 1 mV/div sensitivity but is only listed in the 1995 catalog. And the 7A13 differential comparator which also supports a 1 mV/div sensitivity with a separate 5 MHz bandwidth limit.

author: David Hess
author_rank: Super Contributor
timestamp: June 22, 2014, 07:17:27 pm
content: Quote from: Jon_Paul_Clarke on June 16, 2014, 12:08:52 pmMany oscilloscopes essentially do this internally by changing the gain of the input preamplifier which also has the effect of lowering the bandwidth. On the often discussed 2225, this is done by lowering the load (increasing the resistance) at the output of a transconductance stage to multiply the gain by 10 times. Other oscilloscopes like the 2235 series do this for their highest sensitivity setting or settings by lowering the emitter resistance in a transconductance stage by a factor of 2.5 (5mV/div to 2mV/div) for a minor bandwidth hit and this is common in both old and modern DSOs which often have a different bandwidth for each of their higher sensitivity settings.

author: owiecc
author_rank: Frequent Contributor
timestamp: June 22, 2014, 07:37:59 pm
content: Quote from: plesa on June 16, 2014, 01:23:38 pmI have disassembled one. Needed to change the fan on it. I can show you few photos now, more will come soon. I need to do proper hi-res photos of the boards. Note the hidden button inside

author: David Hess
author_rank: Super Contributor
timestamp: June 22, 2014, 07:54:42 pm
content: Quote from: EEVblog on June 16, 2014, 12:00:37 pmI looked at this as well but differential inputs, high common mode range, and high common mode rejection are too useful to leave out when dealing with low level measurements which more than doubles the complexity so I chose the 7A22/AM502/7A13 route as being more economical.I forget which exactly but I believe the same engineer who designed the mentioned Tektronix differential amplifiers also designed the Preamble (bought by LeCroy) amplifiers.I think 20 MHz is a little optimistic but excess noise would not matter when bandwidth limiting and noise reduction is available from a DSO. The only caveat I would add to a simple x10 probe amplifier is that it should have a compensation adjustment so the probe can be used with it and the oscilloscope without further compensation adjustment.

author: plesa
author_rank: Frequent Contributor
timestamp: June 23, 2014, 10:10:08 pm
content: Quote from: owiecc on June 22, 2014, 07:37:59 pmThanks a lot for sharing. It is more complex than I expected.Hi res photos will be helpful.It is nice piece of equipment, I'm impressed what has been designed 20 years back ;-)

author: Jon_Paul_Clarke
author_rank: Contributor
timestamp: June 25, 2014, 04:27:47 am
content: Quote from: David Hess on June 22, 2014, 07:17:27 pmI had a funny feeling that BW was somehow inversely proportional to voltage sensitivity. I'm guessing that there is a rough correlation to do with the Q of the cct.

author: David Hess
author_rank: Super Contributor
timestamp: June 25, 2014, 07:47:45 pm
content: Exactly what happens depends on the circuit configuration.With the 2225, the output impedance of the transconductance stage is inversely proportional to the bandwidth and they actually added a little bit of capacitance to further lower it so the x10 switch was intended to do dual duty by selecting magnification and bandwidth limiting which make sense because otherwise excessive noise would render high sensitivity useless anyway. The 7A15A works in a completely different way to achieve the same result. DSOs do the same thing but on the digital side with their high resolution mode.With other designs, the loss of bandwidth is minor and just a side effect of getting all of the available gain out of a given number of stages. It is just more economical that way. Would you rather have a maximum sensitivity of 5mV/div and constant bandwidth or a maximum sensitivity of 2mV/div or even 1mV/div with a minor hit to the bandwidth and very little extra design cost? Higher performance (more expensive) vertical amplifiers are less likely to suffer from this issue and "constant bandwidth" may be an advertised feature.If the input referred noise is high enough, then extra sensitivity is wasted unless the bandwidth can be limited. The only fast amplifier, 100 MHz in this case, with a sensitivity better than 5mV/div in the Tektronix 7000 series is the 7A13 and it includes a switchable 5 MHz bandwidth limit. Otherwise it is a constant bandwidth vertical amplifier and its noise at 1mV/div and full bandwidth is readily apparent. I actually measured it at almost 0.5 divisions RMS (almost 500uV RMS and its specification is 400uV RMS or better) which neatly shows why oscilloscope sensitivities usually top out somewhere between 1mV/div and 5mV/div.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 26, 2014, 03:57:45 am
content: Hi,If you look at input sections of the classic Tektronix scopes 465 etc and the 7A18 and 7A26 plugins for the 7000 series. The signal path is very similar.The input attenuator is arranged in 1, 2, 5 sequence. 10x attenuators are added to the signal path for 10, 20, 50x attenuation.The basic sensitivity, with the input attenuator set to zero attenuation, in most of the Tektronix scopes, is 10mV per division. For 5mV/div 2x amplification is added to the signal chain.To obtain 500uV /div a 20x amplifier would be needed.To maintain a 100 MHz bandwidth, the amplifier needs a GBW product of 2GHz.Regards,Jay_Diddy_B

author: Jon_Paul_Clarke
author_rank: Contributor
timestamp: June 26, 2014, 05:53:10 am
content: Thanks David and Jay,That information makes a lot of sense. That's true about making specs to a price, otherwise every CRO that came out would be no holds barred and be absolutely awesome in features and design. I remember Dave(EEVBlog Dave) mentioning something about how Tektronix scopes (DSO's anyway) arrived at a certain way of displaying information that was different to other products from other companies. Tektronix replied back saying something to Dave about how that they have always designed their 'scopes. So my point being is that I guess, some manufacturers can have a design philosophy that lasts decades (Years not Bandwidth!) and may take a lot of effort to problem solve for newer models for adding those extra features.Also having a large Gain BW for the Cct in the order of 2Ghz just to maintain an operating BW of 100Mhz sounds about right. I guess it's a bit like the gain on ye olde Op-amps: Infinite Gain!! - But it will cost you in practice.Thanks again for the Info.Oh, By the way: I think I'll be getting a Hitachi v-1050f. The 2225 is nice and small but the Hitachi seems to tick all of the boxes for me. Now to save...Jon

author: David Hess
author_rank: Super Contributor
timestamp: June 26, 2014, 02:43:33 pm
content: Quote from: Jay_Diddy_B on June 26, 2014, 03:57:45 amYou are in a maze of twisty little vertical amplifier building blocks, all alike.The 7A26 and later amplifiers benefited from integration which allowed functions like paraphase amplifiers for switchable and variable gain blocks.The 2225 series has fewer custom ICs than the 2235 series. That and other differences make me suspect it was intended as a cost reduced version.QuoteThe 2225 series did not do it but the 2235 series and later oscilloscopes include a set of low impedance attenuators after the input amplifier buffer which is a common feature in later oscilloscopes. This is something the older 7A13 does as well.QuoteWhen I do calibration, I usually go through the schematics to find out what the basic sensitivity is because a couple of the Tektronix service manuals have incorrect calibration procedures. Usually this is the second to the highest sensitivity.QuoteI am not sure where you get 20x for the 2225 unless you are treating the differential amplifier as two single ended amplifiers. Its basic sensitivity is 5mV/div so the switchable differential amplifier is x10. The 2235 is the same but has a switchable x2.5 amplifier for 2mV/div.QuoteAre you counting from the input to the CRT deflection plates?

author: David Hess
author_rank: Super Contributor
timestamp: June 26, 2014, 02:50:50 pm
content: Quote from: Jon_Paul_Clarke on June 26, 2014, 05:53:10 amThe Hitachi looks nice and easy to maintain. I think they or another Japanese brand was suppose to have the sharpest CRTs after the Tektronix 547 era. I wonder how much noise is shown on the CRT at 500uV/div where it apparently operates at full bandwidth.

author: Jon_Paul_Clarke
author_rank: Contributor
timestamp: June 27, 2014, 10:24:21 am
content: Well Dave,When I get one I'll let you know! I'll do some experiments to find out.

author: ivaylo
author_rank: Frequent Contributor
timestamp: June 28, 2014, 05:44:01 pm
content: So why sensitivity better than 500uV is so difficult in an oscilloscope? Theoretically it should only be a matter of amplification, no?

author: KJDS
author_rank: Super Contributor
timestamp: June 28, 2014, 06:07:56 pm
content: Quote from: ivaylo on June 28, 2014, 05:44:01 pmI may have got my maths wrong, but a quick calculation shows that with a 1meg input resistance and 100MHz of bandwidth, that's 1.3mV of rms noise.

author: ivaylo
author_rank: Frequent Contributor
timestamp: June 28, 2014, 07:31:17 pm
content: QuoteWhat would be the formula for this if you don't mind?And if input impedance is the obstacle here, there are instruments with even higher impedance measuring way bellow .5mV (voltmeters, spectrum analyzers, etc.), no?

author: David Hess
author_rank: Super Contributor
timestamp: June 28, 2014, 07:46:20 pm
content: Quote from: KJDS on June 28, 2014, 06:07:56 pmIt is not that bad because the input resistance is shunted by the input capacitance. 20pF would make the effective noise bandwidth only 8kHz and the noise do to the input resistance 15 microvolts RMS. But that does nothing for the noise of the input buffer which will be considerable because it is essentially a small gate (low capacitance) RF JFET or MOSFET. You can verify this by shorting out the input to the oscilloscope and observing that the noise level barely changes if it changes at all.It is interesting to note that the Tektronix 7A22 which uses low noise but slow JFETs in its input stage does indeed get close to the calculated input noise level for a 1 megohm input resistance shunted by 47 picofarads and has a maximum input sensitivity of 10 microvolts per division to match it but it still needs low pass filtering after the input amplifier to be useful.

author: David Hess
author_rank: Super Contributor
timestamp: June 28, 2014, 07:55:57 pm
content: Quote from: ivaylo on June 28, 2014, 07:31:17 pmhttp://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noiseIntegrated noise bandwidth will be about 1.6 times higher than the bandwidth of a single pole response.QuoteThese instruments make measurements over very limited bandwidths which are displayed over larger bandwidths.

author: pascal_sweden
author_rank: Super Contributor
timestamp: August 02, 2015, 03:28:04 pm
content: Quote from: EEVblog on June 16, 2014, 12:00:37 pmWhat is the current status of this project?

author: AccountRemovedPerUsersRequest
author_rank: Regular Contributor
timestamp: August 02, 2015, 04:58:39 pm
content: Since I'm not a RF designer myself in any standard, I'm also giving mental support for this project :-)Axel.

author: TimFox
author_rank: Super Contributor
timestamp: August 02, 2015, 08:43:30 pm
content: The input impedance is not the relevant parameter to calculate thermal noise.The correct parameter is the source resistance (real part of the source impedance).This could include any series resistance inside the CRO amplifier as part of the input protection circuit.The amplifier input device (JFET) also has a noise voltage (quoted as a density per "root Hz") and a noise current (another density) that contributes a third noise voltage that increases with increasing source impedance.Only if the input is open-circuited does the shunt resistor that determines the 1 megohm input resistance become the source resistance.

author: tautech
author_rank: Super Contributor
timestamp: February 29, 2016, 01:40:48 am
content: Stumbled on this thread while searching for other stuff.It needs updating.The Siglent SDS1000X series has a full BW 500uV range;http://www.siglentamerica.com/pdxx.aspx?id=1369&T=2&tid=1As described in this thread:https://www.eevblog.com/forum/testgear/siglent-sds1000x-series-oscilloscopes/msg825532/#msg825532New model in the series:SDS1202X-Ehttp://www.siglentamerica.com/pdxx.aspx?id=5109&T=2&tid=1

author: innkeeper
author_rank: Unknown
timestamp: June 17, 2017, 06:40:36 pm
content: An analog scope to add to the 500 uv/div listLeader LBO-516 (also the lab-volt AA-798 - institutional re-badge version)100mhz 3 channel delayed timebase scope.

author: bson
author_rank: Unknown
timestamp: June 18, 2017, 01:06:05 am
content: Quote from: EEVblog on June 16, 2014, 12:00:37 pmx10, DC-500MHz widebandUsing a TI THS3202 CFB op amp, in two stagesWorks like a charm even using cheapo 2L FR-4 (dirtypcbs).At some point, when I cease being this lazy or pigs fly whichever comes first I'm planning to panel mount one of these in a small metal box with a tiny toroidal and a dual rail regulator...

author: Marco
author_rank: Super Contributor
timestamp: June 18, 2017, 08:57:40 am
content: Quote from: KJDS on June 28, 2014, 06:07:56 pmIt's the shunt capacitance on the 9 Meg divider leg which determines the noise, should be in the range of 100 uV.With active x10 probes you might be able to quarter that, with active x1 probes quarter it again. All theoretical limits obviously.

author: Andreas
author_rank: Super Contributor
timestamp: June 18, 2017, 01:01:13 pm
content: Quote from: tautech on February 29, 2016, 01:40:48 amHello,but for what?a 1 Meg input impedance gives 1800uV (eff) or around 12 mVpp noise at 200 MHz.so without bandwidth limiting this is not very useful.With best regardsAndreas

author: Marco
author_rank: Super Contributor
timestamp: June 18, 2017, 01:37:28 pm
content: Quote from: Andreas on June 18, 2017, 01:01:13 pmThe impedance is a lot lower for most of that bandwidth because of capacitance.

author: PartialDischarge
author_rank: Super Contributor
timestamp: June 18, 2017, 01:45:35 pm
content: As mentioned the 7A22 plugin does 10uV/div which is very useful for measuring noise in SMPS. My recently acquired nicolet sigma scope, a rare one, does 100uV/div but is 12bit and only 5mhz, in certain situations it is usable and useful

author: Andreas
author_rank: Super Contributor
timestamp: June 18, 2017, 04:25:59 pm
content: Quote from: MasterTech on June 18, 2017, 01:45:35 pmHello,10uV/div is of course benchmark. Question how is the noise floor / which bandwidth do you have to set to take measurements?My scope has only 2mV/div but has up to factor 50 of zoom (which is possible due to 16 bit ADC) resulting in 40uV/div.At 100 kHz the noise floor is around 100uVpp.Of course you can get lower than that by further reducing bandwidth.with best regardsAndreas

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: June 18, 2017, 06:16:25 pm
content: Quote from: bson on June 18, 2017, 01:06:05 amAre those PCBs available somewhere or are they eval boards for this part? What did you want the toroidal coil for?

author: PA4TIM
author_rank: Super Contributor
timestamp: June 18, 2017, 06:50:06 pm
content: I missed the Tek 547 (or other models from that line) with the 1A7A plugin. This is capable of 10uV /div and then there was the differential E plugin 50uV/divhttp://www.pa4tim.nl/?p=3708

author: mk_
author_rank: Regular Contributor
timestamp: June 18, 2017, 08:29:37 pm
content: Quote from: Neomys Sapiens on June 18, 2017, 06:16:25 pmTI THS3202 (http://www.ti.com/product/THS3202) is NRND :-(

author: Marco
author_rank: Super Contributor
timestamp: June 18, 2017, 10:24:48 pm
content: Quote from: mk_ on June 18, 2017, 08:29:37 pm"Just" use a single THS4303 instead.

author: David Hess
author_rank: Super Contributor
timestamp: June 19, 2017, 12:47:32 pm
content: Quote from: Andreas on June 18, 2017, 04:25:59 pmTektronix was quantitative and conservative about their noise specifications so you can just look it up. The 7A22 is better than 16uVrms over its entire 1 MHz bandwidth which is about 80uVpp. Assuming that the 1/f corner is significantly lower (I suspect it is about 10kHz), over a 100kHz bandwidth, that should be 25uVpp so about 5 times better than your oscilloscope.There are a couple of things worth noting. The 7A22 has a fully differential input so its noise is automatically 3dB higher than a single ended design. Its input stage also has a cascode to support high common mode voltage with high common mode rejection and this also increases input noise. Yet with all of that, it still has lower noise simply because its low bandwidth and 47pF inputs allow the use of larger geometry low noise devices.To get some idea of how much worst case (1) added noise comes from a differential input with cascode for high common mode range makes, compare the 100 MHz differential 7A13 with a standard singled ended 100 MHz vertical amplifier; the former has 400uVrms noise specified although I measured both of mine at about 200uVrms while I measured the 7A18A at about 20uVrms so a ten times difference. On the other hand, while the 7A13 is very noisy, its common mode rejection can make measurements that are impossible for the 7A18 because of added common mode noise.The differential input is actually an advantage despite doubling the input noise because such low levels of noise would be compromised by the ground loop produced using a single ended input. *All* of the low input noise and high sensitivity amplifiers that Tektronix made, and there were several, have differential inputs for this reason. Without the differential inputs, the low input noise and high sensitivity are useless. There is a reason the 100 MHz Tektronix P6046 low voltage differential probe was such a popular product; its differential inputs allow measurements which are otherwise impossible.Could a modern design do better? I doubt it except maybe at the lowest frequencies where 1/f noise dominates. Modern JFETs are only slightly better than what Tektronix used.(1) The 7A22 is slow enough at 1 MHz that its first stage has gain unlike the 100 MHz 7A13 so the added noise is less. Faster oscilloscope amplifiers cannot get away with that.

author: bson
author_rank: Unknown
timestamp: June 19, 2017, 05:32:31 pm
content: Quote from: Neomys Sapiens on June 18, 2017, 06:16:25 pmNo, they're just prototype boards I made. The toroidal is for a quiet linear power supply.