Pulsegenerator 1-5ns and 1V at 50Ohm - Page 1
Forum section: electronics / beginners

author: McCain
author_rank: Newbie
timestamp: February 18, 2020, 08:30:26 am
content: Good Morning all,please refrain from my not so good english. I had to do a lotUse translators. sorry.I need a Pulse generator to test our electronic devices at work. I Hope that I can build myself. I would like to have a pulsewhich drives approx. 1 volt at 50 ohms and a rise time of 1-5ns.The pulsewidth is almost irrelevant and can be anything between 1us and 500us, thatwouldn't be that important. Only the rise time and the amplitude is interesting.Has anyone happened to see a post here in the forum that I could recreate?That would be awesome.I appreciate any help.Thank you very much.McCain

author: radiolistener
author_rank: Super Contributor
timestamp: February 18, 2020, 09:24:49 am
content: you can use si5351 adafruit module, it has 50 ohm output and allows to to produce square wave with 1 ns rise time.https://learn.adafruit.com/adafruit-si5351-clock-generator-breakoutIn order to control it, you can use some cheap one dollar STM32F103 arduino module (blue pill)https://stm32-base.org/boards/STM32F103C8T6-Blue-Pill.html

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 18, 2020, 11:24:39 am
content: How about this one made by forum member Leo Bodnar?http://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=124&products_id=295

author: Marco
author_rank: Super Contributor
timestamp: February 18, 2020, 02:51:03 pm
content: Microcontroller/IDE of choice to generate the pulse, hex inverter to buffer it, a resistor to reduce it to 1V.

author: PartialDischarge
author_rank: Super Contributor
timestamp: February 18, 2020, 03:52:49 pm
content: I made a pulser based on the Tektronix 109 concept, with a mercury realy from ebay. The nice thing about it is that it is not limited to 1.8V or 5V, it can go to 300V or more which can be useful sometimes.

author: ejeffrey
author_rank: Super Contributor
timestamp: February 18, 2020, 05:29:18 pm
content: 1-5 nanoseconds is not particularly hard to achieve. You can generate the pulse with anything (a microcontroller, 555, or a debounced push-button) then use a fast device to square it up. Fast logic gates like the 74AUC series or (LV)PECL will easily do this with resistors to set the output level appropriately -- in fact they are overkill as they have sub ns rise times. A 74AUC logic gate won't drive the needed output current but you can put multiple gates in parallel to increase current load. The PECL families are emitter coupled bipolar logic so the pulse amplitude isn't as accurate as a CMOS based gate. If you are happy with the slower end of the 1-5 ns range then you can use correspondingly slower logic families.An more flexible solution is to go with high speed comparators. The nice thing here is that comparators are often designed with high current output drivers and separate output supply voltage that can be varied independently of the input.Avalanche and mercury relay pulsers are capable of much greater performance if you need it, but

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 18, 2020, 05:36:19 pm
content: Hi,Question for the OP:What accuracy are you looking for on the 1V?Jay_Diddy_B

author: McCain
author_rank: Newbie
timestamp: February 19, 2020, 02:05:17 pm
content: As an output voltage, it would be nice if there were something between 500mV and 2V. It would be great to set it, but I would also be satisfied with a fixed release.With the Adafruit_Si5351, however, the oscilloscope image at the 112 MHz setting looks very strange. The risetime is about 5ns but a rectangle is no longer recognizable.Would be nice if the signal looks like the 13.553 MHz but without the overshoot.Pictures are herehttps://learn.adafruit.com/adafruit-si5351-clock-generator-breakout?view=allBut thank you very much for all the answers, I'll read them through. If someone has more interesting information, I would be very happyThank you very much

author: Gyro
author_rank: Super Contributor
timestamp: February 19, 2020, 03:27:18 pm
content: Quote from: McCain on February 19, 2020, 02:05:17 pmThe cycle time of a 112MHz signal is less than 10ns. Before you get near the top, it's time to turn around and go back down again.P.S. The way they have the module hooked up on a breadboard, you can't expect decent quality signals - they don't show how they are scoping the signal, but if they are just using the ordinary scope probe ground lead then that would explain the terrible ringing on the 13.553MHz signal, and the poor risetime. The edges of the 10kHz signal are ringing just as badly by the way - the scope timebase is just too slow to show it.

author: David Hess
author_rank: Super Contributor
timestamp: February 20, 2020, 06:26:05 pm
content: Quote from: ejeffrey on February 18, 2020, 05:29:18 pmEven the later generations of bipolar TTL logic can produce an edge that fast. I swapped out the 74LS140 dual 4-input NAND buffer in my function generator for an Advanced Schottky replacement to get a faster edge on the function generator's sync output pulse.Personally my choice would be to use a 74LVC125 tri-state buffer (1) to drive a transistor cascode to drive a parallel terminated source. This allows for easy adjustment of pulse amplitude and makes it easier to get a very clean output. This is essentially a modern version of how many reference level pulse generators like the Tektronix PG506 work.But AC logic (advanced CMOS logic) or many of the more recent CMOS logic families like LVC can generate a 1 nanosecond edge directly.(1) The LVC logic family can operate at 5 volts for higher performance and I think it is the fastest commonly available CMOS logic family when used this way.

author: MasterT
author_rank: Frequent Contributor
timestamp: February 20, 2020, 06:50:26 pm
content: Use analog switch lvc4066, easy to set voltage at one side 0-5V and get sharp pulse at the other end. No need to worry about logic level conversion like for logic chips.

author: Gyro
author_rank: Super Contributor
timestamp: February 20, 2020, 07:02:40 pm
content: Quote from: MasterT on February 20, 2020, 06:50:26 pmNote that the turn-on and turn-off times are very slow compared to 74LVC typical logic speeds (up to 20/34ns, even at VCC of 6V, and slower at lower supplies)...https://assets.nexperia.com/documents/data-sheet/74LV4066.pdfA transmission gate is a nice idea in other respects though.

author: MasterT
author_rank: Frequent Contributor
timestamp: February 20, 2020, 09:25:56 pm
content: Quote from: Gyro on February 20, 2020, 07:02:40 pm? Page 12:https://assets.nexperia.com/documents/data-sheet/74LVC4066.pdfRise time < 2nsec at 30pF load. There are 4 switches, sure timing gonna be faster using 2-4 in parallel.

author: Gyro
author_rank: Super Contributor
timestamp: February 20, 2020, 10:26:49 pm
content: Oops, I didn't notice that my LVC search had pulled up a 74LV4066 datasheet hit first. You're quite correct.The figures on page 12 actually relate to input-output risetime (switch is already enabled), but the enable /disable times are similarly fast at 1.9/2.5ns typ. (Table 8 and Fig 16) as long as the VCC is kept up at ~5V... I'm assuming that your intention was to tie the inputs to a well decoupled 1V DC rail and switch the enable pins to create the pulse timing.