Pulse Generator KIts or Ready to Use - Page 1
Forum section: electronics / general

author: max-bit
author_rank: Frequent Contributor
timestamp: October 21, 2015, 06:58:21 pm
content: Pulse Generator (based Jim Williams PG)Ready to Use 48$Payment via PayPal (please contact via personal message)Shipping cost Europe - 5 EuroWorld - 7 $Precise measurementsused oscilloscope:LeCroy LC584AL 1 GHz 8GS/s (rise time ~330-350ps)Pulse the load 50OmPulse the load 1MOmjitter trigger pulse

author: max-bit
author_rank: Frequent Contributor
timestamp: October 27, 2015, 11:56:28 am
content: price adjustment

author: free_electron
author_rank: Super Contributor
timestamp: October 27, 2015, 02:32:47 pm
content: Your pulse does not have a plateau , so you don't really know what the rise time is as the pulse decays before you hit full conduction.I do like the enclosure though

author: tggzzz
author_rank: Super Contributor
timestamp: October 27, 2015, 02:46:15 pm
content: Quote from: free_electron on October 27, 2015, 02:32:47 pmWhile I understand why you say that, does it matter?Provided the test setup isn't the limiting factor, you can measure delta-v and delta-t to get the risetime of this particular pulse.

author: macboy
author_rank: Super Contributor
timestamp: October 27, 2015, 03:20:37 pm
content: Quote from: tggzzz on October 27, 2015, 02:46:15 pmNo, you can't. Not unless you can see the top of the pulse. The problem with a short "hill" type pulse that has no plateau is that you can't know if your scope is displaying the peak value or not. Without the peak value, you can't tell the risetime. Keep in mind that the slew rate (V/second) of the display on the scope will be linked to the magnitude of the pulse. The risetime however is not. That is the fundamental difference.

author: free_electron
author_rank: Super Contributor
timestamp: October 27, 2015, 03:26:08 pm
content: correct. you need to find the 10 and 90% points . to do that you need two plateaus. a lower and an upper.Then you can establish the time needed to traverse the 10-90 point , look at the voltage delta between the points ,and convert it into volts/second. that is the meaningful number.risetime is expressed volts per second. just saying rise time is 260picoseconds means nothing. Is it 260 picoseconds for 1 volt or 260picoseconds for 1000 volts ? ( the latter is a much faster pulse ... ) the slope is much steeper.

author: tggzzz
author_rank: Super Contributor
timestamp: October 27, 2015, 03:50:07 pm
content: Quote from: macboy on October 27, 2015, 03:20:37 pmI think much of that is covered by my caveat/precondition "Provided the test setup isn't the limiting factor".However, I'm irked about the distinction between the risetime and the slewrate - of course you're right. Coming at it from the direction of considering the relative power vs frequency spectrum of the pulse caused me to forget that fundamental, doh!

author: macboy
author_rank: Super Contributor
timestamp: October 27, 2015, 03:56:56 pm
content: Quote from: free_electron on October 27, 2015, 03:26:08 pmNo,rise timeis expressed solely in seconds, or most commonly ns or ps. If you see V/s then it isslew rate, which is a very different thing.

author: free_electron
author_rank: Super Contributor
timestamp: October 27, 2015, 04:27:14 pm
content: You still need to tell me how many volts you traversed to get that risetime. Risetime is meaningless unless you know the voltage swing.For example : they specify on logic gates always what is the power supply voltage at which a particular risetime was measured.Take a simple 4011 for example: Risetime 180nS @ 5v , 90nS @ 10v 65 nS @15v ...Risetime is 10% to 90% of the output swing. But, without knowing what the output swing is, risetime is a useless number.A 1 hz triangle can have a risetime of 1 picosecond... if its vpp is 1.2 picovolt ...That's why, for opamps we dont talk about rise time but slew rate. faster slewrate = higher bandwidth ...so if you are after testing a scope's bandwidth ... you need SLEWRATE ! . risetime is meaningless.to establish slewrate you need the plateau's,

author: macboy
author_rank: Super Contributor
timestamp: October 27, 2015, 05:00:59 pm
content: Quote from: free_electron on October 27, 2015, 04:27:14 pmI am afraid that you are wrong here.On an oscilloscope, the rise time and bandwidth are directly related (though less closely now with digital scopes than with old analog scopes). It is generally accepted that this relationship is BW = 0.35 / risetime. So a 200 MHz scope will have a rise time of approximately 1.75 ns. This rise time will be observed regardless of the magnitude of the pulse (until the slew rate limit is encountered).For opamps, the slew rate is a prime specification, yes. But slew rate for op-amps is not directly related to bandwidth. The GBP is a more useful specification for that. Only when the output swing is very large does slew rate limiting come into play. For high voltage measurements with an oscilloscope, it is quite possible to come up against the slew rate limit before the rise time becomes the limiting factor, just as for an op-amp circuit you can be limited by slew rate before exceeding the bandwidth of the system, when outputting a very large voltage swing.Rise time for an oscilloscope is not useless without a magnitude as you contend. The magnitude is, of course proportional to the input voltage. When thinking in the domain of digital logic levels, slew rate and rise time are related, by the logic levels themselves (the rise time is essentially how long the logic gate takes to slew at full speed from one level to the other). For an oscilloscope, you need to think differently. There is no fixed voltage. It is proportional to the input. And for that reason, the rise time is constant regardless of the input magnitude. If the scope has a rise time of 1 ns to a 10 mV pulse, it will have a rise time of 1 ns to a 10 V pulse too. This is despite the fact that the effective slew rate is three orders of magnitude higher in the latter case.Google "oscilloscope rise time and bandwidth". Read.

author: tggzzz
author_rank: Super Contributor
timestamp: October 27, 2015, 05:03:44 pm
content: Quote from: free_electron on October 27, 2015, 04:27:14 pmUm no. The clue is in the name: riseTIME. (BTW, time is measured in seconds (SI abbreviation "s"), not Siemens (SI abbreviation "S").)It is true thatdigital logicsignals are typically measured in terms of the time taken to traverse 10%-90% of the final value, but the pulse generator's output is not a digital logic signal. Even so, a digital logic signal's risetime is measured in seconds, not volts per second.It is also true that a primary characteristic of opamps is the slewrate, measured in volts per second - but that's not relevant here. Similarly EMI/EMC measurements are based on slewrate.As for your triangle wave, please draw an annotated picture showing the voltages and times (in seconds). Then add the slewrate (in volts per second).

author: macboy
author_rank: Super Contributor
timestamp: October 27, 2015, 06:12:34 pm
content: Quote from: free_electron on October 27, 2015, 04:27:14 pmThink about that again. A 1 Hz triangle (assuming equal rise and fall slopes) has a 10-90% rise time of 0.4 seconds. This is completely independent of voltage.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 27, 2015, 06:44:36 pm
content: Possibly some related discussions in this thread:https://www.eevblog.com/forum/blog/eevblog-306-jim-williams-pulse-generator/msg775096/#msg775096From practical experience it seems there are at least a couple types of pulse generators: those that make "peaky" pulses and those that make a wider flat top pulse. From further practical experience it seems that this statement might be applicable when trying to get an accurate measurement: "Provided the test setup isn't the limiting factor".

author: max-bit
author_rank: Frequent Contributor
timestamp: October 27, 2015, 06:46:58 pm
content: OKTo dispel doubtsused oscilloscope:LeCroy LC584AL 1 GHz 8GS/s (rise time ~330-350ps)Pulse the load 50OmPulse the load 1MOmjitter trigger pulse

author: Electro Fan
author_rank: Super Contributor
timestamp: October 27, 2015, 07:07:35 pm
content: max-bit, I'm confident that your pulse gens are solid - I think there is a minimum scope performance needed to correctly observe your pulse gen's full performance capability.Any chance you can put your pulse gen on a scope that is 200MHz or 400MHz or 500 MHz (or all three if possible) and see what it shows for the pulse shape and the rise time? These results could be contrasted with the results shown for the 1 GHz scope used in your post above.Thanks, EF

author: free_electron
author_rank: Super Contributor
timestamp: October 27, 2015, 07:23:50 pm
content: Quote from: macboy on October 27, 2015, 06:12:34 pmYou're right. brain fart on my part. note to self : drink TWO cups of coffee before posting early morning ...

author: max-bit
author_rank: Frequent Contributor
timestamp: October 27, 2015, 07:29:19 pm
content: The rise time is dependent on the rise time of the oscilloscope.oscilloscope 300MHz (Rigol DS2302) RT~ 1-1,1nS

author: tecman
author_rank: Frequent Contributor
timestamp: November 04, 2015, 02:48:52 pm
content: can you post some pix of what you are selling ?paul

author: cs.dk
author_rank: Unknown
timestamp: November 04, 2015, 05:29:19 pm
content: Quote from: tecman on November 04, 2015, 02:48:52 pmPictures is in the ebay link, in first post:http://www.ebay.com/itm/Pulse-Generator-RiseTime-270ps-PulseWidth-600ps-TDR-/262105510628?

author: max-bit
author_rank: Frequent Contributor
timestamp: November 04, 2015, 10:14:38 pm
content: current Auction:eBay auction: #262128187720PRICE 55 $

author: max-bit
author_rank: Frequent Contributor
timestamp: November 19, 2015, 12:51:45 pm
content: price adjustmentlow price only 50 $For details, see first post

author: max-bit
author_rank: Frequent Contributor
timestamp: December 02, 2015, 06:16:06 am
content: Price 48 $