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How to increase TCXO output?
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rcbuck:

--- Quote ---Why don't you use the NC7SZ04 with a 5V supply?
--- End quote ---
I tried that with the SN74LVC1G14 but could only get about 0.2 volts more out of it than when it was running on the 3.3 volt supply. Probably something to do with the TCXO drive level not being high enough.


--- Quote ---If your comparator circuit has hysteresis feedback connecting to the oscillator output......
--- End quote ---
I don't know what the internal circuitry of the comparator looks like. It does have internal hysteresis according to the data sheet. The TCXO output level into the comparator was about 1.0 volts Pk-Pk. It is probably loading it somewhat as the wave form isn't square on the negative portion of the cycle. I am only interested in counting pulses so as long as there is no ringing I am good.
edavid:

--- Quote from: rcbuck on May 03, 2019, 11:47:48 pm ---
--- Quote ---Why don't you use the NC7SZ04 with a 5V supply?
--- End quote ---
I tried that with the SN74LVC1G14 but could only get about 0.2 volts more out of it than when it was running on the 3.3 volt supply. Probably something to do with the TCXO drive level not being high enough.

--- End quote ---

That doesn't really make sense.  If the drive level is high enough to make the Schmitt trigger switch, you should get full output.  Was the input AC coupled?

In any case, the NC7SZ04 would behave differently.
rcbuck:

--- Quote ---That doesn't really make sense.
--- End quote ---
I agree, but the that is what I was seeing on the scope. The output from the TCXO is AC coupled with a 1 nF cap. The data sheet says the output has to be AC coupled.

I breadboarded the NC7SZ04 this morning using a 1 meg ohm feedback resistor. The NC7SZ04 Vcc was connected to the 5 volt power supply feed. Screen shot is attached. As you said, it behaves differently. The input pin is showing 3.36 V Pk-Pk and the output pin is showing 5.36 V Pk-Pk. The power supply DC levels are actually 3.26 volts and 4.99 volts. So the Pk-Pk values may be picking up random noise to create the higher readings. The 3.36 volt input reading is probably due to the feedback resistor.

The scope leads are both in the 10X mode. If I change the input probe to 1X, it kills the output from the NC7SZ04. That is why I am going to use the comparator. The 1.0 volt Pk-Pk output from the TCXO is just barely enough to drive the buffer. If any stray capacitance were to show up in the PCB traces, it could drop the level enough that the buffer isn't triggered. Of course, if you hand picked the buffer you may be able to get around that issue. But why take the chance?
edavid:

--- Quote from: rcbuck on May 04, 2019, 05:29:52 pm ---The scope leads are both in the 10X mode. If I change the input probe to 1X, it kills the output from the NC7SZ04.

--- End quote ---

A 1X scope probe usually has a capacitance of about 130pF.  At 16MHz, the reactance is 75ohms, obviously a heavy load on the TCXO.  I don't think it's a meaningful test.
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