Using a sinewave OCXO as a timer input source

[g0mgx]

Hi Gang

I want to use a 10 MHz OCXO oscillator as an input to a STM32 clock; the oscillator swings +/- 2V and I need to convert this to a square wave 0-3.3V.

I've tried using a simple comparitor but the circuit fails over about 1Mhz, I've tried a simple transistor switch feeding a 74HC04 gate x 3 but still there is a lot of junk in the output signal.

Can anyone suggest an easy way to convert my sine wave into a logic level square easily?

I'm struggling with what should be a very simple circuit.

Many thanks

Mark
G0MGX

[Manul]

The simplest what comes to my mind (may not be best, but should be ok). I assume you need 3.3V logic out. Notice a schmitt trigger input inverter. You can choose freely (but it needs to be fast enough), for eg. SN74LVC1G14.

[Doctorandus_P]

Are you sure you need a square wave?
Virtually all uC's are designed to run from a crystal, and have therefore already the circuitry inside to run from a sinewave.
Go read the datasheet of your STM32 again and look at the different options for the clock input.

[g0mgx]

Thanks - I'll look at the datasheet again - a riveting read.

How worried do I need to be about the logic level? THe sinewave is +/-2V and the TIM input is 0-3.3V?

Mark

[g0mgx]

Thanks.

Is that LTSpice? I keep seing this again and again - must read up.

Mark

[Manul]

Thanks - I'll look at the datasheet again - a riveting read.

How worried do I need to be about the logic level? THe sinewave is +/-2V and the TIM input is 0-3.3V?

Mark

So you want this 10Mhz for clock or timer input? Anyway, yes, you should worry about levels, to not hit negative or positive above Vdd.

If you plan to run a coax from 10Mhz source or there will be considerable distance you should also take care about impedance matching.

[g0mgx]

So you want this 10Mhz for clock or timer input?

Yes indeed, I'm trying to teach myself STM32Cube programming (having migrated from STM32 on Arduino) - I am trying to write an algorithm to discipline the OCXO from a 1PPS GPS signal.

Its just a technical learning exercise but kind of fun.

Mark