I have a square signal (fixed but can be between 12MHz and up to 48MHz) and I would like to create every 8 clocks a pulse as brief as possible, no more than 1/4 of the period.
First, a couple of loose constraints:
– voltage is at 1.8V but I could have a shift level up to 5V if needed.
– I need the pulse every 8 times, but I would be fine with every 16 or every 32 times.
The key objective is to have the most SIMPLEST approach. Please avoid any answer suggesting a teraflop super computer!
Similarly, FPGA would really make sense but it's like killing a mosquito with a bazouka.
One option consists of using an Atmel 8-bit chip such as AtTiny85 but it's limited to 20MHz so I'm not sure if it could really work or not.
I have read this page with great interest: http://ued.udjat.nl/counter/ and I'm wondering if I could use a similar stratagem.
I prefer AtTiny because of the small package, then Atmel, then Cypress, then Microchip but I'm listening for any option. Is there any option to do something without a "micro processor"?
Best Answer
You can solve this problem with just a couple of parts. TI makes logic parts in their 74AC logic family that operate correctly down to 1.5V. Use a 4 bit counter as shown below to repeatedly count from 8 to 15. Use the RCO output, which is a one clock wide pulse to reload the counter and to also drive an R/C circuit to produce the narrow pulse that you require.
If you desire to produce the pulse for every 16 input cycles then just connect the D input to GND instead of being pulled up to the VCC rail.