The vibration frequency refers to the actual frequency of the oscillating circuit that works with the crystal resonator. The vibration frequency is determined by the crystal resonator and is affected by the MCU, external load capacitance, PCB stray capacitance, and the like.
Measurement method The vibration frequency is calculated by the following equation.
Load resonance frequency, fr: resonance frequency, Cs: load capacitance, C0, C1: equivalent circuit constant
Measuring method 1
Measuring equipment and devices
Oscillation circuit
Frequency counter
Amplifier (or oscilloscope with output signal)
Probe
2. Prepare the measuring device as shown below. Please extend the range of the Y axis in the oscilloscope as much as possible.
3. Keep the probe as close as possible to the oscillator circuit.
4. Read the frequency from the frequency counter.
note
Do not let the probe touch the oscillating circuit. Due to the input capacitance of the probe, the actual oscillation frequency will decrease.
Please note that the frequency accuracy shown on the oscilloscope is not sufficient.
Note the sample rate or average of the digital oscilloscope due to quantization errors.
Measuring method 2
Measuring equipment and devices
Oscillation circuit
spectrum analyzer
Antenna (coaxial cable that can be used as an antenna)
2. Prepare the measuring device as shown below.
3. Keep the antenna as close as possible to the oscillator circuit.
4. Read the peak frequency of the spectrum analyzer response.
note
Please do not let the antenna touch the oscillation circuit.
Use a small-scale spectrum analyzer to measure the response to improve accuracy.
When measuring the frequency, it is important not to let any object touch the oscillation circuit in order to prevent the influence on the probe. If the probe contacts the oscillating circuit to connect the probe capacitance, the oscillation frequency will be shifted.
Oscillation circuit: measuring frequency using a counter
Oscillation circuit: Frequency measurement by spectrum analyzer
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