Help about square waveform generation!

Thread Starter

davidgrohl

Joined Jun 18, 2014
2
Hi all,
I'm a new forum user. I need your help. I would to generate a square waveform @1MHz or less more. I need to add this functionality to a board equipped with a STM32F107 CPU. I'm finishing board schematics but I can't find a way to generate a good waveform. The output voltage has to go from 0V to 3.0V. I try to search for a DAC but it seems to be too slow for what I need. Can you give me some indications about that.
Thanks a lot.

P.s. Sorry for my english :)
 

Thread Starter

davidgrohl

Joined Jun 18, 2014
2
Oscillator is 3.3V output. I need 3.0V
I need a programmable output too. My square generation should be stoppable. Any suggestions?
 

Papabravo

Joined Feb 24, 2006
12,397
Sure. Read the specs carefully and note that they will work over a range of Vcc. Then look for an oscillator with an enable pin. So the four pins would be Vcc, GND, ENABLE, and CLKOUT.

http://www.aextal.com/AE331.pdf

Looking carefully, I see that Vdd can be in the range of 3.0V to 3.6V. Almost all parts are designed this way for a reason. It is very hard to control Vcc to an exact, to 2 decimal places, value.

PS. Give me some credit for reading your original post and seeing that you needed a 3V supply.
 

Papabravo

Joined Feb 24, 2006
12,397
3.3V to 3.0V = voltage divider. Zener diode if you want it more accurate.

Bob
Action of a voltage divider depends on load impedance and is very hard to control accurately and repeatedly. Using Vdd = 3.0 V is a far superior solution.
 

BobTPH

Joined Jun 5, 2013
2,023
And with a 3.0V supply the oscillator will be able to drive 3.0V into any load? Or does it also depend on load impedance?

Bob
 

MrChips

Joined Oct 2, 2009
19,273
You can use the STM32F107 to generate the square wave. There are a whole bunch of timers built into that chip.
 

THE_RB

Joined Feb 11, 2008
5,430
Someone has to ask...

WHY do you need to make the micro generate a squarewave of 1MHz with some adjustability? What will that connect to?

If you provide more information we can suggest more (and better) options. :)
 

Papabravo

Joined Feb 24, 2006
12,397
And with a 3.0V supply the oscillator will be able to drive 3.0V into any load? Or does it also depend on load impedance?

Bob
Well I believe that a CMOS push pull driver will drive more loads, especially capacitive loads, than anything else I can imagine, but let's consult the datasheet.

It will drive 5 TTL loads @ 1.6 mA per TTL load or 8 mA, or 15 pf of capacitive load with 6 ns rise and fall times.
 
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