(1) Damping of Series Resonance (also known as Variable Frequency Resonance) Circuit
By adding resistance in the resonant circuit, resonance can be suppressed. This resistor is called a damping resistor. An example of adding a damping resistor (represented by R in the figure) is shown.
When a damping resistor is used in series with a series resonator, the Q of the resonator is derived as follows.
For example, we can combine the part constants used in the test of Figure 3-2-4 into this formula. If the output impedance of the signal source is 50 ohms for resistor R, Q=6.3 is obtained, indicating the presence of strong resonance; If the resistor R is high, Q becomes smaller, thereby weakening resonance. Therefore, you can see that adding a resistor greater than 50 ohms for this purpose can weaken resonance.
Usually, to suppress resonance, resistors are selected so that Q is set to 1 or less.
(2) Non oscillatory conditions of series resonant circuit
To eliminate overshoot, undershoot, or ringing of pulse waveforms such as digital signals, a resistor satisfying the following formula is used to satisfy the non oscillation condition of the LCR series resonant circuit.
Formula (2) results in Q being equal to or less than 0.5.
(3) Damping of Parallel Resonant Circuit
On the contrary, when damping resistors are used in parallel with parallel resonators, as shown in the figure, the Q of the resonator is derived as follows:
In this case, the smaller the resistance, the weaker the resonance.
Example of Resistance Damping
