Nanosecond Duty cycle PWM generation

[Pr4vi]

Hello guys,

I am looking for simple methods of generating a square wave 5V with adjustable duty cycle of ATLEAST 50ns. Not too concerned about the switching frequency at the moment. The purpose is to suit pulsed power generation. Therefore a pulse repetition rate of 0.1-1Hz should be more than enough.

I am not convinced the conventional method of comparing a triangular wave with a reference would give me that precision. Any ideas would be highly appreciated.

Thanks

 

[VEBill]

The phrase "at least 50ns" is a bit confusing.

 

[MacGyverS2000]

I assume you mean a pulse width with a minimum resolution of 50ns?

A one-instruction/Hz processor running at 20MHz would give you the resolution you ask for, and a 1-10Hz repetition rate would be easily achievable. Typical crystals give you 50ppm accuracy, and better can be achieved with MEMS oscillators.

It doesn't get any simpler than that. A PIC chip and supporting components could output a pulse like that for <$5 in single quantities.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[electricuwe]

To achieve 50 ns pulsewidth resolution is by far not a very demanding target. I have designed such a generator about 15 years ago using 74AC logic devices and about 10 years ago using CPLD devices from Altera. With state of the art PLD devices you should easily be able to get 10 ns of resolution.

The method to use is the digital equivalent of the analog approach you have described.

 

[MikeHalloran]

I did something similar some years ago, loading an EPROM with bit patterns representing duty cycles, then running the low order address lines with a free running clock and counter, and using the high order address lines to select which stored patterns to use.

My circuit had four outputs, and was used to (crudely) microstep a stepping motor.






Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

A bigger question is why you'd need any such speeds for: "pulsed power generation"

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DHambley]

...then, once you have that low-level pulse from any of the suggestions above, are you looking for a way to drive a power switch following that?

 

[MikeHalloran]

I'm guessing the power stage is the subject of next semester's lab....




Mike Halloran
Pembroke Pines, FL, USA