I've struggling trying to get a 10MHz square wave generator circuit to work. I'm using the circuit below with a 10MHz crystal and the SN74HC04 hex inverter. I'm powering the inverter with 5V.

The problem I'm having is that I get a sine wave in the output instead of a square wave. I get a sine wave of 10MHz, 9V peak to peak and about 3.2V RMS. What am I doing wrong here? How do I get the square wave I want? Thanks in advance.

 

What is the make and model of your oscilloscope and its bandwidth?
What type of probe are you using on the oscilloscope?
SN74HC04 is not a Schmitt-Trigger inverter.

 

What is the make and model of your oscilloscope and its bandwidth?
What type of probe are you using on the oscilloscope?
SN74HC04 is not a Schmitt-Trigger inverter.

I have a EZ oscilloscope that can go up to 150MHz. I'm using the coax connector that came with it. Do you think that using the Schmitt-Trigger inverter makes a difference here?

 

How are you implementing this? On a solderless breadboard? Perfboard? PCB?

 

I'm using the coax connector that came with it.

A coax cable will have way too much capacitance at 10MHz.
You need a 10:1 oscilloscope probe.

 

How are you implementing this? On a solderless breadboard? Perfboard? PCB?

Yes, I'm using a breadboard.

 

I'm using a breadboard.

Yes, but what type of breadboard?

What is the output peak to peak voltage?

 

Yes, I'm using a breadboard.

How about posting a scope image of the 'ringing' waveform.

 

A coax cable will have way too much capacitance at 10MHz.
You need a 10:1 oscilloscope probe.

Using the 10:1 probe, the signal looks more square but it has a lot of noise, harmonics. I'm thinking about ordering the Schmitt trigger inverter. What is better for this application, a Schmitt trigger inverter or a LT1719 comparator? I have a module that I'm trying to make it work and it needs a square wave clock input of at least 10MHz.

 

Yes, but what type of breadboard?

What is the output peak to peak voltage?

I get a sine wave of 10MHz, 9V peak to peak and about 3.2V RMS.

 

I get a sine wave of 10MHz, 9V peak to peak and about 3.2V RMS.

The 74HC04 has a max voltage rating of 7V.
How are you getting 9V?

That plug-in breadboard has a lot of stray capacitance that is likely corrupting your signal.

 

How about posting a scope image of the 'ringing' waveform.

The first picture is with the coax probe. The second picture is with the 10:1 probe.

 

The 74HC04 has a max voltage rating of 7V.
How are you getting 9V.

That plug-in breadboard has a lot of stray capacitance that is likely corrupting your signal.

I don't know how it is giving me a 9V peak to peak.

 

Getting circuits to work at 10 MHz on a solderless breadboard is not at all easy -- it can be done, I know someone that was somewhat notorious for getting a 20 MHz function generator to work on a set of solderless breadboards, but he most definitely knew what he was doing and he went to some rather extreme and ridiculous lengths to get it to work, primarily for the bragging rights of having done it.

A good rule of thumb is to abandon solderless breadboards once you are trying to work with frequencies above 1 MHz, particularly for analog circuits, and expect significant distortion in higher frequency digital signals due to corruption of the harmonics.

 

Getting circuits to work at 10 MHz on a solderless breadboard is not at all easy -- it can be done, I know someone that was somewhat notorious for getting a 20 MHz function generator to work on a set of solderless breadboards, but he most definitely knew what he was doing and he went to some rather extreme and ridiculous lengths to get it to work, primarily for the bragging rights of having done it.

A good rule of thumb is to abandon solderless breadboards once you are trying to work with frequencies above 1 MHz, particularly for analog circuits, and expect significant distortion in higher frequency digital signals due to corruption of the harmonics.

Paying for a PCB board that I don't even know if it's going to work is tough. How would you test this circuit without a breadboard?

 

Paying for a PCB board that I don't even know if it's going to work is tough. How would you test this circuit without a breadboard?

I use vector board with some copper shielding for those types of prototypes.
https://forum.allaboutcircuits.com/...justing-frequency-counter.204571/post-1959952



With proper chip bypassing.

 

Solderless spring contact boards are one thing, but there are MANY other ways to prototype circuits that perform as well as a PCB.

 

I use vector board with some copper shielding for those types of prototypes.
https://forum.allaboutcircuits.com/...justing-frequency-counter.204571/post-1959952

With proper chip bypassing.

Nice! Thank you for sharing. Do you think the Schmitt trigger inverter will make a difference? Is the LT1719 comparator a better option?

 

Using a 74HC14 instead of an '04 would be a good start - the circuit specifies a schmitt trigger device for a good reason.

 

Nice! Thank you for sharing. Do you think the Schmitt trigger inverter will make a difference? Is the LT1719 comparator a better option?

What type of bypass capacitors are you using for each chip (as close as possible to each chips VCC and GND pins) on that plug-in breadboard?