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Analog Input and Output Signal Acquisition and Distribution
Published in Fernando E. Valdes-Perez, Ramon Pallas-Areny, Microcontrollers, 2017
Fernando E. Valdes-Perez, Ramon Pallas-Areny
When the input terminals of an amplifier are connected to ground, its output voltage is not zero as would be expected. Instead, the output is a dc signal whose value depends on the amplifier gain and the resistances between the inputs and ground. To analyze these effects, the amplifier can be modeled by adding a voltage source called offset voltage and a dc current source between each input terminal and ground. Figure 9.16 shows the equivalent circuit when connecting a differential voltage to an instrumentation amplifier. The instrumentation amplifier is a differential amplifier with very high input impedances. The presence of the dc current sources requires a low resistance path between each input and the ground. For this reason, the common terminal for the signal is normally connected to the amplifier ground. Furthermore, it is not possible to connect the signal to the amplifier using just a capacitor in series with each terminal, because the capacitors would be charging and would end up saturating the amplifier.
Amplifiers and Filters
Published in Clarence W. de Silva, Sensor Systems, 2016
Usually, an instrumentation amplifier is also a differential amplifier (sometimes termed difference amplifier). It generates the difference between two signals, which has many uses as mentioned in the context of instrumentation amplifiers. Ground-loop noise can be a serious problem in single-ended amplifiers. Ground-loop noise can be effectively eliminated using a differential amplifier because noise loops are formed with both inputs of an amplifier, and hence, these noise signals are subtracted at the amplifier output. Since the noise level is almost the same for both inputs, it is canceled out. Any other noise (e.g., 60 Hz line noise) that might enter both inputs with the same intensity will also be canceled out at the output of a differential amplifier.
Designing a Low-Cost ECG Sensor and Monitor: Practical Considerations and Measures
Published in Daniel Tze Huei Lai, Rezaul Begg, Marimuthu Palaniswami, Healthcare Sensor Networks, 2016
Ahsan H. Khandoker, Brian A. Walker
However, one of the most important parameters relevant to an ECG amplifier is the amplifier’s CMRR, which would determine the amount of common mode noise present at the output of the amplifier. It can be shown using rigorous mathematical analysis (Peyton and Walsh 1993) that at low frequencies, the simple two op amp instrumentation amplifier has increased CMRR compared to that from an amplifier using the three op amp configuration. The two op amp instrumentation amplifier does have two main limitations – one being the minimum amount of gain which can be achieved, which is usually restricted to between 2 and 4 depending on how the resistors are connected (Northrop 2004). Also, at high frequencies, the two op amp instrumentation amplifier has a nonlinear frequency response which results in the bandwidth being one half of that of the three op amp configuration. This is due to signals at one of the amplifier’s inputs passing through one more op amp stage than the signals at the other input. However, because an ECG system operates at low frequencies and requires high gain, these limitations are not really of any importance.
A Novel Differential Voltage Current Conveyor (DVCC) Based Instrumentation Amplifier
Published in IETE Journal of Research, 2022
John Vista, Nonglen Meitei Pheiroijam, Harika Pamu, Huirem Tarunkumar, Ashish Ranjan
The current scenario of electronics world is enriched with amplifiers, rectifiers, filters, oscillators, comparator, analog to digital converters, and many other signal processing circuits. Among these analog signal processing circuits, Instrumentation amplifier (IA) is the basic one and widely used to amplify the useful differential signals and to suppress any unwanted common mode signals [1]. On the other hand, several applications like medical instrumentation [2–4], read out integrated circuits for biosensors [5], data acquisition systems [6,7], electro cardiography [8,9], etc. have been reported that pronounce the importance of IA.