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

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LC series resonant absorption circuit

In practice, the function of the snubber circuit is to remove the letter of a certain frequency in the input signal. Figure 4-65 shows an snubber circuit constructed using an LC series resonant circuit. VT1 in the circuit constitutes a primary amplifier, U is the input signal, and U is the output signal of this amplifier. Ll and Cl constitute an LC series resonant absorption circuit whose series resonant frequency is fo, which is connected between the input end of VT1 and the ground.

(1) The input signal frequency is fo. For the signal with the frequency fo in the input signal, since the resonant frequency is the same as that of L1 and Cl, the series circuit of L1 and Cl has a small impedance to it, and the input signal with the frequency of five is bypassed to the ground by L1 and Cl and cannot be added. At the base of VT1, VT1 cannot amplify the 矗 signal, and of course there is no signal with the frequency fo in the output signal.
(2) The input signal frequency is higher or lower than the stone. For signals with frequencies above or below fo in the input signal, due to the unequal resonant frequencies with L1 and Cl, the L1 and Cl series circuits are detuned, their impedance is large, and their input signals are not beside Ll and Cl. Road to the ground, but added to the base of VT1, amplified by VT1 output. It can be seen from the frequency response characteristics of this reactor that there is no signal with a frequency of fo in the output signal.

The series resonant high-frequency boost circuit uses a high-frequency boost circuit composed of an LC series circuit. VT1 in the circuit constitutes a first-level common-emitter amplifier, and L1 and C4 form an LC series resonant circuit for boosting high-frequency signals. The resonant frequency of the L1 and C4 series resonant circuits is five, which is higher than the highest frequency of the operating signal of this amplifier.
Since the impedance of the L1 and C4 circuits is the smallest at resonance, the negative feedback resistance is minimized in parallel with the emitter negative feedback resistor R4, so the amplification factor at this time is the largest. In this way, the high-frequency signal close to fo is improved. The frequency response characteristic curve of the amplifier in the figure shows that the high-frequency response curve when L1 and C4 are not added is a dotted line, and the solid line when L1 and C4 are added, which is obviously solid. The high frequency response is better than the dotted line.
For input signals with frequencies much lower than fo, the L1 and C4 circuits have no boosting effect. Because the L1 and C4 circuits are detuned, their impedance is large, and the negative feedback resistance at this time is R4.

The signal frequency of the input LC parallel resonant circuit is very broad and contains a signal whose frequency is the resonant frequency. In the input signals of many frequencies, the circuit only resonates with the signal whose frequency is the resonant frequency, and the impedance of the circuit is the most dog. The resonant circuit has a frequency bandwidth. In circuit analysis, it can be considered that the signals in the frequency band are amplified or processed in the same way as the signals of the resonant frequency; however, the signals whose frequencies deviate from the resonant frequency. Summary: The width of the frequency band is related to the size of the Q value. If the Q value is large, it is considered that it is not amplified or processed. This is because the circuit analysis requires a narrow frequency band; the Q value is small and the frequency bandwidth is small.