However, for very low-attenuation circuits high Q -factor , issues such as dielectric losses of coils and capacitors can become important. A very frequent use of these circuits is in the tuning circuits of analogue radios. A College Text-book of Physics 2nd ed. This is exactly the same as the resonance frequency of an LC circuit, that is, one with no resistor present. Under those conditions the bandwidth is [29]. A key parameter in filter design is bandwidth.

Other configurations are not described in such detail, but the key differences from the series case are given. The bandwidth is related to attenuation by. The average power dissipated in a series resonant circuit can be expressed in terms of the rms voltage and current as follows:. Likewise, the resistance in an RLC circuit will “damp” the oscillation, diminishing it with time if there is no driving AC power source in the circuit. Both band-pass and band-stop filters can be constructed and some filter circuits are shown later in the article. The value of the damping factor determines the type of transient that the circuit will exhibit. For the IF stage in the radio where the tuning is preset in the factory, the more usual solution is an adjustable core in the inductor to adjust L. We can see then that at resonance, the two reactances cancel each other out thereby making a series LC combination act as a short circuit with the only opposition to current flow in a series resonance circuit being the resistance, R.

Series Resonance Circuit

In a series RLC circuit there becomes a frequency point were the inductive reactance of the inductor becomes equal in value to the capacitive reactance of the capacitor. D 1 and D 2 are arbitrary constants determined by boundary conditions.

The resonant frequency of this circuit is [19]. The resonance of a series RLC rislnanti occurs when the inductive and capacitive reactances are equal in magnitude but cancel each other because they are degrees apart in phase.

In fact, it happens that Q is the inverse of fractional bandwidth. In this design, the core made of a high permeability material that has the effect of increasing inductance is threaded so that it can be screwed further in, or screwed further out of the inductor winding as required.


At a higher frequency X L is high and at a low frequency X C is high. Circuits which will resonate in this sdrie are described as underdamped and those that will not are overdamped.

In the filtering application, the resistor becomes the load that the filter is working into. Since this power depends upon the square of the current, these resonant curves appear steeper and narrower than the resonance peaks for current above.

On the other hand, if driven by a constant current, there would be a maximum in the voltage which would follow the same curve as the current in the series circuit.

Resonant RLC Circuits

It is defined as the peak energy stored in the circuit divided by the average energy dissipated in it per radian risonanyi resonance. Likewise, the other scaled parameters, fractional bandwidth and Q are also reciprocals of each other.

The Reactance value of a capacitor has a very high value at low frequencies but quickly decreases as the frequency across it increases. The resonance frequency is defined as the frequency at which the impedance of the circuit is at a minimum. Analog circuits Electronic filter topology. Power in a Series Resonant Circuit The average power dissipated in a series resonant circuit can be expressed in terms of the rms voltage and current as follows: By the quadratic formulawe find.

Posted on November 29th Posted on December ssrie 3: It is still possible for the circuit to carry on oscillating for a time after the driving source has been removed riisonanti it is subjected to a step in voltage including a step down to zero. In practice, this objective requires making the circuit’s resistance R as small as physically possible for a series circuit, or alternatively increasing R to as much as possible for a parallel circuit.

The resonant frequency for an RLC circuit is the same as a circuit in which there is no damping, hence undamped resonance frequency. Also sketch the corresponding current waveform for all frequencies.


A wide band filter requires high damping. Such a circuit could consist of an energy storage capacitor, a load in the form of a resistance, some circuit inductance and a switch — all in series. As a series resonance circuit rlx functions on resonant frequency, this type of circuit is also known as an Acceptor Circuit because at resonance, the impedance of the circuit is at its minimum so easily accepts the current whose frequency is equal to its resonant frequency. Figure 11 is a band-stop filter formed by a parallel LC circuit in series risonantk the load.

Taking the magnitude of the above equation with this substitution:. Circuits where L and C are in parallel rather than series actually have a risonqnti impedance rather than a minimum impedance.

Series Resonance in a Series RLC Resonant Circuit

You may have noticed that during the analysis of series resonance circuits in this tutorial, we looked at bandwidth, upper and lower frequencies, -3dB circukti and quality or Q-factor. The critically damped response represents the circuit response that decays in the fastest possible time without going into oscillation.

If the inductance L is known, then the remaining parameters are given by the following — capacitance:. The inductive reactance value of an inductor increases linearly as the frequency across it increases.

From the above equation for inductive reactance, if either the Frequency or the Rc is increased the overall inductive reactance value of riwonanti inductor would also increase.

The second case requires a low impedance source so that the voltage is dropped across the antiresonator when it becomes high impedance at resonance.