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The Electronics of Microphones and Loudspeakers
Published in Michael Filimowicz, Foundations in Sound Design for Embedded Media, 2019
A preamplifier, or preamp, increases the voltage of a weak signal so that it can be usable in other parts of a circuit. (A preamp is different from a power audio amplifier, which is designed to drive a loudspeaker. We’ll return to power amps later in this chapter). There are a wide range of preamp designs, for use in a variety of applications, some unrelated to audio. Our purposes require a preamp fast enough to process the high frequencies of an audio signal, with an output between 0 and 5 V, the safe operating range for the microcontroller. For convenience, it should run off the 3.3 V/5 V provided by the board. Vendors such as Adafruit and Sparkfun sell electret mics hardwired with an appropriate preamp, mounted on a breakout board complete with power supply. These mics have the additional advantage of adding DC bias to the electret mic’s signal.
Giga-Ohm High-Impedance FET Input Amplifiers for Dry Electrode Biosensor Circuits and Systems
Published in Iniewski Krzysztof, Integrated Microsystems, 2017
Gaetano Gargiulo, Paolo Bifulco, Rafael A. Calvo, Maria Romano, Mariano Ruffo, Richard Shephard, Mario Cesarelli, Craig Jin, Alistair McEwan, André van Schaik
The preamplifier stage is the crucial element of a biopotential measurement system; its main tasks are twofold: first, to sense the microvolt-level voltage between two measuring electrodes while rejecting the common-mode signal; second, by minimizing the dc effect of electrode polarization overpotentials. These unwanted signals are typically three to four orders of magnitude greater than the biopotential of interest demanding a CMRR of greater than 60 dB. Crucial for maintaining the performance of the preamplifier in practice is the input impedance, which should be as high as possible. Typical specifications include an input impedance of greater than 100 mega-ohms. Such a differential amplifier cannot be realized using a standard single operational amplifier (op-amp) design since this does not provide the necessary combination of high input impedance, CMRR, and gain over the required frequency range [2,4].
Vibration Control
Published in Lewis H. Bell, Douglas H. Bell, Industrial Noise Control, 2017
Lewis H. Bell, Douglas H. Bell
The second element in the measurement system is the preamplifier. When using a velocity pickup, a preamplifier is not required. However, when using a piezoelectric accelerometer, a preamplifier is always required. Basically, the preamplifier serves two useful purposes: it increases the level of the transducer signal, which is small, and it provides an impedance-matching device between the transducer and the signal-processing equipment. Most transducer manufacturers supply an assortment of preamplifiers as optional equipment. In many cases, the preamplifier is directly integrated into the accelerometer packaging.
Application of Behavioral Psychology in Clothing Design from The Perspective of Big Data
Published in Applied Artificial Intelligence, 2023
The behavioral psychological ECG signal is a low-frequency signal with a small amplitude, so the preamplifier is required to have low noise and low drift. Before the electronic pulses enter a line leading to an amplifier, the preamplifier amplifies them by improving the signal-to-noise ratios. Moreover, a pulse-shaping circuit may linearly amplify and shape the output pulses of the preamplifier. The current-sensitive preamplifier, the parasitic-capacitance preamplifier, and the charge-sensitive preamplifier are the three primary types of preamplifiers that are accessible. This determines the quality of the obtained behavioral psychological ECG signal. The DC amplifier can amplify the behavioral ECG signal with very small frequency, but the DC amplifier has a drift phenomenon, which limits the input range. Therefore, through analysis and research, the differential circuit is the best input form, and choosing symmetrical components can effectively suppress the zero drift. Circuits with differential inputs take the voltage difference between two different input signals. A single-ended input is less able to withstand electromagnetic interference (EMI) than a differential input. Moreover, they can present balanced input impedance and reject common-mode voltage better than single input circuit and the majority of the time, symmetrical components are used for analyzing three-phase electrical power systems. By breaking down a three-phase unbalanced system into two sets of balanced phasors and a set of single-phase phasors, or symmetrical components, it is possible to optimize fault analysis.