A quasi-peak detector is a type of electronic

detector A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...

rectifier A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an inve ...

. Quasi-peak detectors for specific purposes have usually been standardized with mathematically precisely defined dynamic characteristics of

attack time In telecommunication, attack time is the time between the instant that a signal at the input of a device or circuit exceeds the activation threshold of the device or circuit and the instant that the device or circuit reacts in a specified manner, or ...

, integration time, and

decay time In electronics, fall time (pulse decay time) t_f is the time taken for the amplitude of a pulse to decrease (fall) from a specified value (usually 90% of the peak value exclusive of overshoot or undershoot) to another specified value (usually 10 ...

or fall-back time. Quasi-peak detectors play an important role in

electromagnetic compatibility Electromagnetic compatibility (EMC) is the ability of electrical equipment and systems to function acceptably in their electromagnetic environment, by limiting the unintentional generation, propagation and reception of electromagnetic energy whic ...

(EMC) testing of electronic equipment, where allowed levels of

electromagnetic interference Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrost ...

(EMI), also called radio frequency interference (RFI), are given with reference to measurement by a specified quasi-peak detector. This was originally done because the quasi-peak detector was believed to better indicate the subjective annoyance level experienced by a listener hearing impulsive interference to an AM radio station. Over time standards incorporating quasi-peak detectors as the measurement device were extended to frequencies up to 1

GHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one ...

, although there may not be any justification beyond previous practice for using the quasi-peak detector to measure interference to signals other than AM radio. The quasi-peak detector parameters to be used for EMC testing vary with frequency . Both

CISPR The ''Comité International Spécial des Perturbations Radioélectriques'' (CISPR; en, International Special Committee on Radio Interference) was founded in 1934 to set standards for controlling electromagnetic interference in electrical and elec ...

and the U.S.

Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisd ...

(FCC) limit

EMI EMI Group Limited (originally an initialism for Electric and Musical Industries, also referred to as EMI Records Ltd. or simply EMI) was a British transnational conglomerate founded in March 1931 in London. At the time of its break-up in 2012, ...

at frequencies above 1

with reference to an average-power detector, rather than quasi-peak detector. Conceptually, a quasi-peak detector for EMC testing works like a peak detector followed by a lossy integrator. A voltage impulse entering a narrow-band receiver produces a short-duration burst oscillating at the receiver centre frequency. The peak detector is a rectifier followed by a

low-pass filter A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filt ...

to extract a

baseband signal In telecommunications and signal processing, baseband is the range of frequencies occupied by a signal that has not been modulated to higher frequencies. Baseband signals typically originate from transducers, converting some other variable into a ...

consisting of the slowly (relative to the receiver centre frequency) time-varying amplitude of the impulsive oscillation. The following lossy integrator has a rapid rise time and longer fall time, so the measured output for a sequence of impulses is higher when the pulse repetition rate is higher. The quasi-peak detector is calibrated to produce the same output level as a peak-power detector when the input is a continuous wave tone . The CISPR quasi-peak detector is used in EMC testing and is defined in Publication 16 of the International Special Committee on Radio Interference (CISPR) of the International Electrotechnical Commission (IEC). The CISPR quasi-peak detector applied to most conducted emissions measurements (0.15 - 30 MHz) is a detector with an attack time of 1 ms, a decay time of 160 ms and an IF filter setting of 9 kHz. The quasi-peak detector applied to most radiated emissions measurements (30 - 1000 MHz) has an attack time of 1 ms, a decay time 550 ms and an IF filter bandwidth of 120 kHz. In

audio quality measurement Audio system measurements are a means of quantifying system performance. These measurements are made for several purposes. Designers take measurements so that they can specify the performance of a piece of equipment. Maintenance engineers make ...

, quasi-peak rectifiers are specified in several standards. For example

ITU-R 468 noise weighting ITU-R 468 (originally defined in CCIR recommendation 468-4, therefore formerly also known as CCIR weighting; sometimes referred to as CCIR-1k) is a standard relating to noise measurement, widely used when measuring noise in audio systems. The ...

uses a special rectifier incorporating two cascaded charging

time constant In physics and engineering, the time constant, usually denoted by the Greek letter (tau), is the parameter characterizing the response to a step input of a first-order, linear time-invariant (LTI) system.Concretely, a first-order LTI system is a s ...

s. The PPM or peak programme meter used to measure programme levels is actually a quasi-peak reading meter, again with precisely defined dynamics.

Flutter measurement Measurement of wow and flutter is carried out on audio tape machines, cassette recorders and players, and other analog recording and reproduction devices with rotary components (e.g. movie projectors, turntables (vinyl recording), etc.) This measur ...

also involves a standardised quasi-peak reading meter. In every case the dynamics are chosen to reflect the sensitivity of human hearing to brief sounds, ignoring those so brief that we do not perceive them, and

weighting The process of weighting involves emphasizing the contribution of particular aspects of a phenomenon (or of a set of data) over others to an outcome or result; thereby highlighting those aspects in comparison to others in the analysis. That i ...

those of intermediate duration according to audibility.

References

{{Reflist Radio electronics Electromagnetic compatibility Audio engineering

See also

References