Help with obtaining a specific pulse

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Discussion Overview

The discussion revolves around obtaining a specific short pulse from a 1Hz pulse signal. Participants explore various circuit design approaches, including edge detection and the use of specific components, while addressing constraints and requirements for pulse duration and characteristics.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks to generate a short pulse at the low edge of a 1Hz pulse without using capacitors, considering flip-flops as a potential solution.
  • Another participant suggests using a transformer and a diode to filter out the pulse from the descending edge, asking for more details on available circuit elements.
  • A different participant describes an edge detector circuit that requires inverters and mentions using NAND gates for the design, noting the need for inversion depending on the desired pulse edge.
  • Questions are raised about the required pulse duration, with one participant asking for specifics such as whether the pulse needs to be 1 millisecond, 1 microsecond, or 1 nanosecond.
  • A new participant introduces a need for a pulsed 3-volt DC power supply at a nanosecond rate, mentioning the use of ultra-fast step recovery diodes and discussing the challenges of achieving picosecond rates.
  • Another participant comments on the frequency implications of a nanosecond pulse, suggesting the use of germanium circuits and referencing high-frequency clock circuits from modern microprocessors.
  • One participant advises the new contributor to start a separate thread for their specific query, inquiring about the power requirements and whether the pulsing implies continuous operation or a single pulse on demand.

Areas of Agreement / Disagreement

Participants express various approaches and ideas without reaching a consensus on the best method to achieve the desired pulse. Multiple competing views and suggestions remain present throughout the discussion.

Contextual Notes

The discussion includes assumptions about the availability of components and the specific requirements for pulse characteristics, which are not fully defined. There are also unresolved questions regarding the feasibility of achieving very short pulse durations with the suggested methods.

malsch
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Homework Statement



Hi, I have a 1Hz pulse and wish to obtain a very short pulse at the low edge of the 1Hz pulse. The following is what I'm referring to:

5dbfb1132801092.jpg


The Attempt at a Solution



Since I cannot use a capacitor, I was thinking maybe something with flip flops but I'm still a bit stuck.

Thank you
 
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Do you have more information on the available circuit elements you do have?

My first thought is a transformer (converting rate of change of current to a voltage) and a good stiff diode to filter out the pulse from the descending edge.
 
There a lot of these edge detector circuits.

I had to invent one years ago and I tend to use that one all the time.

It works on a rising edge (so you have to invert the input first if you want a falling edge) and it gives a falling pulse (ie 5V then 0V then 5V) so you have to invert that if you want a rising pulse.
In this case, you need both inverters.

In the following circuit, the two NAND gates in the middle form the actual edge detector while 3 of the 4 gates are used as inverters. This is convenient because NAND gates come in ICs with 4 gates in them, like the 74C00.

[PLAIN]http://dl.dropbox.com/u/4222062/edge%20pulse.PNG
 
Last edited by a moderator:
How short do you need the pulse ?
1 millisec, 1 microsec, 1 nanosec ?

Why can't you use a capacitor ?
 


zetrone said:
Hello, I am new here and though I would just ask this here in this thread since it seems relavent.

I need a 3 volt DC power supply that is pulsed (any kind of pulse shape) at a nanosecond rate.

I am 63 years old and not to savey about present day electronic. I started with a 1B3 rectifr tube.

If a picosecond rate could be acheived it would be great. I just ordered one of those ultra fast step recovery diodes...could that be used to make this PULSE power supply?

Thanks,

David

Hmmm... one nanosecond period corresponds to (hmmm...milli micro nano pico ~ kilo mega, giga tera) a one gigahertz frequency. That's pushing microwave frequencies so you're going to probably need a germanium circuit. You can make a germanium bridge rectifier and a 500MHz oscillator from textbook UHF Ham radio circuits. That will give you a roughly absolute value of a sine wave with peaks spaced 1 nanosecond apart. I'd suggest you check out clock circuits for the newer microprocessor chips as they run in the 1-3 gigahertz range now.

Picosecond rates are getting into low infrared frequencies. One is reaching wavelengths (sub-millimeter) more appropriately considered "optics" rather than "electronics". A one picosecond period equals 1 Tera Hertz frequency. You're not going to find cheap off the shelf parts to put that together. A typical source for such high frequencies is an optically pumped terahertz laser.
 
@zetrone: you should probably start a new thread in case this one gets more involved. Just curious, but how much power are you talking about--what is your "load". Does "pulsed at a nanosecond rate" imply continuous 500MHz operation or do you just want a single fast pulse on demand?
 

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