LC series resonant circuit working principle analysis - Database & Sql Blog Articles

LC Series Resonant Absorption Circuit

In practical applications, the main purpose of a snubber circuit is to filter out specific frequency components from the input signal. Figure 4-65 illustrates a snubber circuit that uses an LC series resonant circuit. In this setup, VT1 acts as the primary amplifier, with U representing the input signal and the output signal being taken from the same point. The LC series resonant circuit formed by L1 and C1 has a resonant frequency of fâ‚€, and it is connected between the input terminal of VT1 and ground.

(1) When the input signal frequency matches fâ‚€, the LC series circuit presents low impedance to this frequency. As a result, the signal at fâ‚€ is shunted to ground through L1 and C1, preventing it from reaching the base of VT1. Consequently, VT1 does not amplify this frequency, and no such signal appears in the output.

(2) When the input signal frequency is either higher or lower than fâ‚€, the LC series circuit becomes detuned, leading to a high impedance. This means the signal is not bypassed to ground but instead reaches the base of VT1, where it is amplified and appears in the output. From the frequency response characteristics, it's clear that the output signal lacks any component at frequency fâ‚€.

The series resonant high-frequency boost circuit utilizes an LC series configuration to enhance high-frequency signals. In this design, VT1 serves as a first-stage common-emitter amplifier, while L1 and C4 form an LC series resonant circuit designed to boost high-frequency signals. The resonant frequency of L1 and C4 is set to fâ‚€, which is higher than the maximum operating frequency of the amplifier.

At resonance, the impedance of the L1 and C4 circuit is minimized, effectively reducing the negative feedback resistance in parallel with R4. This results in the highest amplification factor for signals near fâ‚€. The frequency response curve shows that when L1 and C4 are included, the high-frequency response (solid line) is significantly better than when they are not used (dotted line).

For input signals with frequencies much lower than fâ‚€, the L1 and C4 circuit has little to no boosting effect. At these frequencies, the circuit is detuned, resulting in high impedance, and the negative feedback resistor remains R4.

The LC parallel resonant circuit can handle a wide range of input frequencies, but it only resonates with the signal that matches its resonant frequency. At this frequency, the circuit exhibits the lowest impedance. The resonant circuit has a certain bandwidth. In circuit analysis, signals within this bandwidth are treated similarly to the resonant frequency. However, signals outside this range are not significantly affected. The bandwidth is directly related to the Q value: a higher Q value indicates a narrower bandwidth, while a lower Q value allows for a broader range of frequencies to be processed.

Summary: The resonant circuit selectively amplifies or processes signals at its resonant frequency, while signals outside the bandwidth are not amplified. This behavior is crucial in designing circuits that require precise frequency control.