Contents
What is load capacitance of a crystal?
Load capacitance is the amount of external circuit capacitance in parallel with the crystal itself. When specifying a series-resonant crystal, you can ignore load capacitance. This is true because the crystal’s motional inductance and motional capacitance are the only LC components that determine oscillation frequency.
Can quartz be used as a capacitor?
So depending upon the circuit characteristics, a quartz crystal can act as either a capacitor, an inductor, a series resonance circuit or as a parallel resonance circuit and to demonstrate this more clearly, we can also plot the crystals reactance against frequency as shown.
What is crystal motional resistance?
: Motional resistance is the resistive element of the quartz crystal equivalent circuit. This resistance. represents the equivalent impedance of the crystal at natural resonant frequency [series resonance].
Do crystal oscillators fail?
Piezo materials will loose their property when heated beyond the Curie temperature of the material, so overheating is one form to make crystals fail. Piezo materials usually also are brittle so they are susceptible to mechanical shocks which can break them.
Why do we use capacitor in microcontroller?
If the input voltage drops, then a decoupling capacitor will be able to provide enough power to an IC to keep the voltage stable. If the voltage increases, then a decoupling capacitor will be able to absorb the excess energy trying to flow through to the IC, which again keeps the voltage stable.
What is the difference between crystal and oscillator?
They are two different components and power up the processor in different ways. The oscillator provides total connectivity to a processor clock. The crystal forms the oscillator along with other parts such as the trim caps, inverting amplifier, and proper output buffer.
How is drive level of crystal calculated?
Crystal drive level is the amount of power dissipated in a crystal which is usually specified in microwatts or milliwatts. It can be calculated by measuring the excitation current flowing through the crystal.
Which is the best capacitor for a crystal?
Unfortunately, this ignores the stray capacitance (Cstray), and won’t give you the best results. Even if you are guestimating Cstray you will get better results taking it into account, but it means just using a capacitor 2* CL won’t work: 13pF is much too high to get the best results from your crystal.
How to choose the right capacitor for your cstray?
If you think the stray capacitance is a bit lower, say 3pF, you might try a 10pF capacitor: There’s an obvious tradeoff between choosing a standard capacitor value, and having a good idea of what your Cstray is, but the above formula should at least explain HOW to determine what value those capacitors should be relative to your crystal.
How can I tell if my capacitors match my Crystal?
We know CL since it’s stated in the crystal datasheet (8 pF), and we know Cstray (say ~5 pF), so all we need to do is test our value for C1 and C2 to make sure that it will match CL taking into account Cstray. A commonly tossed around rule of thumb is to start with a pair of capacitors two times the CL of the crystal, which will get you to CL.
What is the ppm of a shunt capacitor?
Essentially, the load capacitance of the crystal, C L, is set equal to the combination of the capacitors you’re adding and the shunt capacitance of the crystal, so The ppm figures specify the (in)accuracy of the crystal (when properly used): 5 ppm is 5 parts per million.