Probing the crystal for oscillation frequency measurement
measurement, it might lose the signal when you probe it due to large capacitace
on the probe. To solve this I use active probe (small capacitance) to measure the
waveform and oscillation frequency of crystal.
My question is, if I don't have active probe and I only have normal oscilloscope
probe in hand. How would I measure oscillation frequency of crystal ?
Should I series/parallel something between probe and crystal ?
And how to evaluate the value(maybe R,L,C) you would like to series/parallel ?
Thanks a lot
You appear to be using this crystal in an IC that has an internal oscillator active circuit.
1. You can put your probe on the point where the active circuit has a low impedance point like the output of a gate or transistor.
2. You can make a similar oscillator circuit on a breadboard and measure the output of the oscillator.
3. You can make a high impedance probe by putting a 1 pF capacitor on the end of your probe. The amplitude measurement will be wrong, but the frequency will be correct.
4. If you have a radio receiver or spectrum analyzer, you can make a small loop on the end of a coax and put it near the crystal.
Putting the circuit close to the Scope, and using a short coax cable it should be enough to put the "hot" lead of the coax close (without touching!) to the high amplitude node of the oscillator to see the signal clearly.
Modifying the probe with inductive coupling with frequency, but it only can apply to frequency more than 10MHz.
Kindly refer for more details : " Oscillations and computer simulation " book available at our Ebook updload download forum.
Crystal Oscillator Design and testing application notes at microchip's website might also be helpful.
Cya
I still don't know how to do it.
Series a capacitor on the end of the probe?
Thanks