Crystal oscillator simulation

Posted on Feb 6, 2014

Originally I was going to call this posting `Crystal Oscillator Blues`. This is given because things have not been going well with constructing the crystal oscillator for the GPS Disciplined Oscillator, as outlined in my last posting ( GPSDO - Crystal Oscillator ). However, a couple of things have gone quite well, interestingly well as it happens.

Crystal oscillator simulation
Click here to download the full size of the above Circuit.

There are some interesting points in here, and I actually do think the oscillator is operating just fine, based on the observations made. So where to start. First interesting point is CircuitLab -. I wanted to determine what the circuit should be doing in theory. So I started to look up a suitable SPICE application and came across CircuitLab. The best way to describe this application is like comparing a standalone email program, say Microsoft Outlook or Mozilla Thunderbird, to Google Mail. It`s all online - interesting. But what`s more impressive is just how user friendly it is. Within 2 minutes I was designing the resonator circuit and then testing it. Unbelievable! Figure 1 shows what it looks like, using the resonator circuit of the oscillator as an example. So exactly what should the oscillator with amplifier board (resonator) actually be doing Good question! This is where a circuit simulator such as CircuitLab is useful. Figure 2 shows the schematic for the circuit and Figure 3 shows the output at the measurement points indicated. All good so far, but this is certainly not what I saw when making measurements with an actual OCXO and amplifier board. First I made measurements with an unloaded system - per the circuit above minus the 10 pF capacitor (representing the connecting cable) and the 2. 2 kOhm load resistor. Figure 4 shows the simulated circuit, Figure 5 shows the simulated output and Figure 6 shows a capture of...

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