What is the negative resistance of crystal oscillator?
What is the negative resistance of crystal oscillator?
Negative Resistance
English abbreviation: – R
Unit symbol: Ω
The negative resistance of crystal oscillator is also known as negative impedance,
which means that by increasing the circuit gain to offset the crystal oscillator from its own and equivalent circuit obstacles,
so as to achieve the purpose of normal vibration, its gain value is negative resistance.
Obviously, it is not enough to realize the successful start-up of crystal oscillator. We need the crystal oscillator to work at a stable output frequency,
so we must consider leaving enough gain margin to ensure that the crystal oscillator can continue to vibrate normally after starting.
Special reminder: negative resistance is not a built-in parameter of crystal oscillator, but it is a very important performance index in the design of oscillation circuit.
According to the requirements of negative resistance of oscillation circuit:
In order to obtain a stable oscillation circuit, the negative resistance (- R) of the oscillation circuit IC is at least five times that of the crystal oscillator,
that is, the absolute value | - R | > 5R. For example, if the total impedance of the crystal oscillator circuit is 30 Ω,
the negative resistance of the IC should be at least - 150 Ω, so as to effectively guarantee the stability of the oscillation circuit.