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Guarding and Shielding
Published in Anton F. P. van Putten, Electronic Measurement Systems, 2019
There is some confusion between the different amplifier configurations. For example, sometimes an operational amplifier is called an instrumentation amplifier, but this is just a special configuration in which three operational amplifiers are involved. Such a three-amplifier configuration has improved features with respect to a single operational amplifier: in particular the CMRR and the input impedance are improved. An operational amplifier can be considered as just a building block which can be used either as a differential amplifier or as a single active element, depending on how a few external passive components are connected. For our purposes it will be sufficient to present only some basic concepts which describe the quality of the differential amplifier. Consider the general schematic layout for a grounded circuit as illustrated in figure 8.37.
Analog Circuit Cells
Published in Wai-Kai Chen, Analog and VLSI Circuits, 2018
Kenneth V. Noren, John Choma, J. Trujillo, David G. Haigh, Bill Redman-White, Rahim Akbari-Dilmaghani, Mohammed Ismail, Shu-Chuan Huang, Chung-Chih Hung, Trond Saether
The fact that two general source excitations applied to a four-port system can be separated into a voltage component that appears only differentially across the two system input ports and a single-ended common-mode voltage component that is simultaneously incident with both of the system input ports makes it possible to achieve signal discrimination in a differential circuit. In particular, a differential amplifier can be designed so that it amplifies the differential component of two source signals while rejecting (in the sense of amplifying with near zero gain) their common-mode component. Signal discrimination is useful whenever an electronic system must process low-level electrical signals that are contaminated by spurious inputs, such as the voltage ramifications of electromagnetic interference or the biasing perturbations induced by temperature. If the two input ports of a differential amplifier are geometrically proximate and have matched driving point input impedances, these spurious excitations impact the two input ports identically. The undesired inputs are therefore common-mode excitations that can be rejected by a differential amplifier that is well designed in the sense of producing output port responses that are sensitive to only differential inputs.
Multistage Amplifiers
Published in Amir M. Sodagar, Analysis of Bipolar and CMOS Amplifiers, 2018
Nowadays, in a wide variety of analog circuits and systems it is preferred to differentially transfer, amplify, and process the signals. This is because of the advantages that this approach has over the traditional single-ended signal approach, most importantly, better noise immunity and larger voltage swing. All the amplifiers studied so far are designed to amplify single-ended signals. The differential amplifier can be thought of as an amplifier that is capable of amplifying a differential signal and providing its output in differential form. This is illustrated in Figure 5.20(b).
Application of Behavioral Psychology in Clothing Design from The Perspective of Big Data
Published in Applied Artificial Intelligence, 2023
The common mode rejection ratio of the single op amp differential amplifier circuit is affected by the resistance matching accuracy of the external circuit. Where, the perfect op-amp has an infinitely low input resistance. It establishes the degree of output voltage reduction caused by the application of a load. When a differential signal needs to be amplified in the presence of a potential substantial common-mode input, such as significant electromagnetic interference, a high CMRR is necessary (EMI) and the common mode rejection ratio of the amplifier itself. Signals or noise that flows in a pair of lines in the same direction are referred to as the common mode. The voltage shared by both input terminals of an electrical device is known as a common-mode voltage. Whereas, signals or noise that travel along a pair of lines in the opposite directions are said to be in the differential mode voltage. A differential voltage between two conductors is used to convey the signal in the majority of electrical circuits. In practice, the total common-mode rejection ratio cannot reach the ideal state, so the circuit structure needs to be improved. Either raising differential voltage gain or reducing common mode voltage gain will help us increase the CMRR. Emitter resistance RE should be raised to increase CMRR. CMRR should ideally be unlimited. CMRR would typically have a value of 100 dB. The use of a buffer stage in series with a differential amplifier with an in-phase parallel structure is the pre-stage design scheme that is often selected.
Development of a miniature electromagnet probe for the measurement of local velocity in heavy liquid metals
Published in Journal of Nuclear Science and Technology, 2022
Gen Ariyoshi, Hironari Obayashi, Toshinobu Sasa
From previous research, the electrical voltage induced between the electrodes is in the microvoltage order [13]. In addition, it is important to suppress the electrical noise to the signal pass between the signal source and the amplifier. Hence, the manufactured EM probe was directly connected to a low-noise differential amplifier (CA-461F2, NF Corporation), as shown in Figure 8(b). With this combination, electrical wirings can be shortened, and enough quality signal can be obtained. The detected induced voltage is amplified with a gain of 100 by the differential amplifier first and amplified again with a gain of 2000 by the DC amplifier. As mentioned in Section 1, the electromagnetic induction method potentially has a rapid time response. Once the sampling frequency for the amplified signal is determined, the frequency leads directly to the time response of the probe. In this measurement, the rapid sampling frequency, 20 kHz, was applied to the digitization of the amplified signal.
Calibration of Electrocardiograph (ECG) Simulators
Published in NCSLI Measure, 2018
Steven Yang, Brenda Lam, Chris M. N. Ng
The unit under test (UUT), an ECG simulator, is a differential voltage source with output signal amplitude in the millivolt range. A differential amplifier with high common mode rejection ratio is essential for the measurement of ECG signal with a multimeter or oscilloscope. At the SCL, the amplitude, frequency/rate and waveform settings of the UUT are calibrated by the readings from the laboratory’s reference voltage measuring system based on digital sampling. The system comprises an AC/DC differential amplifier, a high-speed digital multimeter (DMM) and a control computer. The digital sampling technique enables the reconstruction and characterization of the signal waveform, which is particularly useful in the measurement of normal sinus or other waveforms in non-sinusoidal wave shape.