Ringing (signal) This article is about ringing in electronics and signals generally. For ringing artifacts in signal processing, particularly image processing, see ringing artifacts. Ringing is undesirable because it causes extra current to flow, thereby wasting energy and causing extra heating of the components; it can cause unwanted electromagnetic radiation to be emitted; it can delay arrival at a desired final state (increase settling time); and it may cause unwanted triggering of bistable elements in digital circuits. Ringy communications circuits may suffer falsing. Ringing can be due to signal reflection, in which case it may be minimized by impedance matching. Ringing can affect audio equipment in a number of ways. Audio amplifiers can produce ringing depending on their design, although the transients that can produce such ringing rarely occur in audio signals. Transducers (i.e., microphones and loudspeakers) can also ring. Jump up ^ Johnson, H. and Graham, M.
Ringing (signal) Clipping (signal processing) An oscilloscope screen of an amplifier "clipping. " The amplifier should be outputting a clean sine wave with rounded tops and bottoms, but instead they are cut off flat, or "clipped". Clipping may be described as hard, in cases where the signal is strictly limited at the threshold, producing a flat cutoff; or it may be described as soft, in cases where the clipped signal continues to follow the original at a reduced gain.
Hard clipping results in many high frequency harmonics; soft clipping results in fewer higher order harmonics and intermodulation distortion components. This PCM waveform is clipped between the red lines In the audio domain, clipping may be heard as general distortion or as pops. In the frequency domain, clipping produces strong harmonics in the high frequency range (as the clipped waveform comes closer to a squarewave).
Example image exhibiting blown-out highlights. The incidence of clipping may be greatly reduced by using floating point numbers instead of integers. Sinc filter. It is an "ideal" low-pass filter in the frequency sense, perfectly passing low frequencies, perfectly cutting high frequencies; and thus may be considered to be a brick-wall filter. Real-time filters can only approximate this ideal, since an ideal sinc filter (aka rectangular filter) is non-causal and has an infinite delay, but it is commonly found in conceptual demonstrations or proofs, such as the sampling theorem and the Whittaker–Shannon interpolation formula.
In mathematical terms, the desired frequency response is the rectangular function: where is an arbitrary cutoff frequency (aka bandwidth). The impulse response of such a filter is given by the inverse Fourier transform of the frequency response: the normalized sinc function. As the sinc filter has infinite impulse response in both positive and negative time directions, it must be approximated for real-world (non-abstract) applications; a windowed sinc filter is often used instead. Brick-wall filters Frequency-domain sinc Ringing artifacts. Image showing ringing artifacts. 3 levels on each side of transition: overshoot, first ring, and (faint) second ring. Same image without ringing artifacts. Introduction The main cause of ringing artifacts is due to a signal being bandlimited (specifically, not having high frequencies) or passed through a low-pass filter; this is the frequency domain description. In terms of the time domain, the cause of this type of ringing is the ripples in the sinc function, which is the impulse response (time domain representation) of a perfect low-pass filter.
Mathematically, this is called the Gibbs phenomenon. There are related artifacts caused by other frequency domain effects, and similar artifacts due to unrelated causes. Causes Description If one has a linear time invariant (LTI) filter, then one can understand the filter and ringing in terms of the impulse response (the time domain view), or in terms of its Fourier transform, the frequency response (the frequency domain view).
Gibbs phenomenon. In mathematics, the Gibbs phenomenon, discovered by Henry Wilbraham (1848) and rediscovered by J. Willard Gibbs (1899), is the peculiar manner in which the Fourier series of a piecewise continuously differentiable periodic function behaves at a jump discontinuity: the nth partial sum of the Fourier series has large oscillations near the jump, which might increase the maximum of the partial sum above that of the function itself. The overshoot does not die out as the frequency increases, but approaches a finite limit. These are one cause of ringing artifacts in signal processing. Description Functional approximation of square wave using 5 harmonics Functional approximation of square wave using 25 harmonics Functional approximation of square wave using 125 harmonics The Gibbs phenomenon involves both the fact that Fourier sums overshoot at a jump discontinuity, and that this overshoot does not die out as the frequency increases. ) whose Fourier expansion is between and History
Step response. From a practical standpoint, knowing how the system responds to a sudden input is important because large and possibly fast deviations from the long term steady state may have extreme effects on the component itself and on other portions of the overall system dependent on this component. In addition, the overall system cannot act until the component's output settles down to some vicinity of its final state, delaying the overall system response.
Formally, knowing the step response of a dynamical system gives information on the stability of such a system, and on its ability to reach one stationary state when starting from another. Time domain versus frequency domain Instead of frequency response, system performance may be specified in terms of parameters describing time-dependence of response. In the case of linear dynamic systems, much can be inferred about the system from these characteristics. Step response of feedback amplifiers With one dominant pole Analysis with. Overshoot (signal) Maximum overshoot is defined in Katsuhiko Ogata's Discrete-time control systems as "the maximum peak value of the response curve measured from the desired response of the system. " The percentage overshoot is a function of the Damping ratio ζ and is given by  The damping ratio can also be found by In electronics, overshoot refers to the transitory values of any parameter that exceeds its final (steady state) value during its transition from one value to another.
Usage: Overshoot occurs when the transitory values exceed final value. Overshoot represents a distortion of the signal.In circuit design, the goals of minimizing overshoot and of decreasing circuit risetime can conflict.The magnitude of overshoot depends on time through a phenomenon called "damping. " Overshoot (bottom of image), caused by using unsharp masking to sharpen an image. This occurs for instance in using the sinc filter as an ideal (brick-wall) low-pass filter. Jump up ^ Ogata, Katsuhiko (1987). Inrush current limiter. An inrush current limiter is a component used to limit inrush current to avoid gradual damage to components and avoid tripping the supply's fuse or circuit breaker.
Negative temperature coefficient (NTC) thermistors and fixed resistors are often used to limit inrush current. NTC thermistors can be used as inrush-current limiting devices in power supply circuits when placed in series with the circuit being protected. They present a higher resistance initially, which prevents large currents from flowing at turn-on. As current continues to flow, NTC thermistors heat up, allowing higher current flow during normal operation. NTC thermistors are usually much larger than measurement type thermistors, and are purposely designed for power applications. Thermistor An NTC thermistor's resistance is high at low temperatures. Fixed resistor Fixed resistors are also widely used to limit inrush current. Applications References See also Soft start. Inrush Current FAQs | Ametherm. Passive or Active Protection for Inrush Current?
There are several component options for inrush current limiting. The two most common alternatives are the use of NTC (Negative Temperature Coefficient) thermistors or various forms of active circuits. However, the most appropriate inrush current suppression technique for a particular application depends on component pricing issues, the equipment's power level, and the frequency at which the equipment is likely to be exposed to inrush currents. No single component solution can be best for every application. Each approach has its own advantages and disadvantages. What is an Inrush Current Limiting Thermistor (Surge Limiter)? Inrush Current Limiters are among the most common design options used in switching power supplies to prevent damage caused by inrush current surges. What Types of Inrush Current Limiting Thermistors are Available? Are NTC Thermistors Common for Inrush Current Protection? What Are Other Uses of NTC Thermistors?
Inrush current. An example of inrush current transients during capacitor bank energization. Transformers When a transformer is first energized, a transient current up to 10 to 15 times larger than the rated transformer current can flow for several cycles. Toroidal transformers, using less copper for the same power handling, can have up to 60 times inrush to running current. Worst case inrush happens when the primary winding is connected at an instant around the zero-crossing of the primary voltage, (which for a pure inductance would be the current maximum in the AC cycle) and if the polarity of the voltage half cycle has the same polarity as the remnance in the iron core has.
(The magnetic remanence was left high from a preceding half cycle). Unless the windings and core are sized to normally never exceed 50% of saturation, (and in an efficient transformer they never are, such a construction would be overly heavy and inefficient) then during such a start up the core will be saturated. Motors Inrush current.