Q factor - Wikipedia
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The upper and lower band edges read from the curve are Hz for fl and Hz for fh. Figure below Below the resonant frequency, the parallel resonant circuit looks inductive since the impedance of the inductor is lower, drawing the larger proportion of current.
Q Factor and Bandwidth of a Resonant Circuit | Resonance | Electronics Textbook
Above resonance, the capacitive reactance decreases, drawing the larger current, thus, taking on a capacitive characteristic.
A parallel resonant circuit is resistive at resonance, inductive below resonance, capacitive above resonance. Impedance is maximum at resonance in a parallel resonant circuit, but decreases above or below resonance. Figure below Parallel resonant circuit: Impedance peaks at resonance.
A low Q due to a high resistance in series with the inductor produces a low peak on a broad response curve for a parallel resonant circuit. Figure below conversely, a high Q is due to a low resistance in series with the inductor. This produces a higher peak in the narrower response curve. The high Q is achieved by winding the inductor with larger diameter smaller gaguelower resistance wire.
Parallel resonant response varies with Q. With increasing Q factor or quality factor, so the bandwidth of the tuned circuit filter is reduced. As losses decrease so the tuned circuit becomes sharper as energy is stored better in the circuit. It can be seen that as the Q increases, so the 3 dB bandwidth decreases and the overall response of the tuned circuit increases.
In many instances a high Q factor is needed to ensure that the required degree of selectivity is achieved. In many RF applications there is a requirement for wide bandwidth operation.
Some forms of modulation require a wide bandwidth, and other applications require fixed filters to provide wide band coverage.
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While high rejection of unwanted signals may be required, there is a competing requirement for wide bandwidths. Accordingly in many applications the level of Q required needs to be determined to provide the overall performance that is needed meeting requirements for wide bandwidth and adequate rejection of unwanted signals. Any oscillator generates what is known as phase noise. This comprises random shifts in the phase of the signal. This manifests itself as noise that spreads out from the main carrier.
As might be expected, this noise is not wanted and therefore needs to be minimised. The oscillator design can be tailored to reduce this in a number of ways, the chief one being by increasing the Q, quality factor of the oscillator tuned circuit. Tuned circuits and filters are often used to remove spurious signals.
The sharper the filter and the higher the level of Q, the better the circuit will be able to remove the spurious signals. Q factor and damping[ edit ] Main articles: For mathematical details about these systems and their behavior see harmonic oscillator and linear time invariant LTI system.
Such a system doesn't oscillate at all, but when displaced from its equilibrium steady-state output it returns to it by exponential decayapproaching the steady state value asymptotically. It has an impulse response that is the sum of two decaying exponential functions with different rates of decay. As the quality factor decreases the slower decay mode becomes stronger relative to the faster mode and dominates the system's response resulting in a slower system.
A second-order low-pass filter with a very low quality factor has a nearly first-order step response; the system's output responds to a step input by slowly rising toward an asymptote. Underdamped systems combine oscillation at a specific frequency with a decay of the amplitude of the signal.