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CHAPTER 4 Electrical Considerations and Electronic Interface
Published in Douglas Self, Audio Engineering Explained, 2012
Figure 4.11 shows a simplified transformerless console input section showing switchable line/microphone operation. At one time transformers were felt to be indispensable in the design of microphone input circuitry. Their chief advantages are a high degree of electrical balance and consequent high common- mode signal rejection. (A common-mode signal is one that is identical at both inputs; typically, induced noise signals are common mode.) In the era of vacuum tubes the input transformer was of course essential. Today's best solid state balanced input circuitry does not mandate the use of transformers, and there are considerable economic advantages to pass on to the user. Only under conditions of high electrical interference might their use be required.
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Published in Farzin Asadi, Electric and Electronic Circuit Simulation using TINA-TI®, 2022
Let’s measure the common-mode gain of the amplifier. In order to do this, add the voltage source VG1 to the schematic (Figure 2.245). Settings of the voltage source VG1 are shown in Figure 2.246. Note that in Figure 2.245, RC1=9.9 kΩ and RC2=10.1 kΩ. If you run the schematic of Figure 2.245, with RC1=RC2=10 kΩ, the output (voltage difference between the collectors) becomes zero since the circuit is symmetric and the input is the same for both transistors. When the output for common-mode signal is zero, the common-mode gain is zero and the CMRR becomes infinity which is desired. However, obtaining a completely symmetric circuit is very difficult (if not impossible) in the real world.
Application of Operational Amplifiers
Published in Bogdan M. Wilamowski, J. David Irwin, Fundamentals of Industrial Electronics, 2018
Carlotta A. Berry, Deborah J. Walter
The differential amplifier has a differential input mode defined as the difference between the two input voltages. The second feature of a difference amplifier is the common mode input, the average of the two input voltages. Ideally, the common mode gain should be zero and only the differential input should be amplified. Typically, the common mode signal represents the noise found in most electric signals, which should be suppressed at the output. To design for this feature, the resistors used in the op amp must be well matched. The common mode rejection ratio (CMRR) is used to measure how well a difference amplifier performs. The CMRRR is the ratio of the differential mode gain to the common mode gain.
Low-cost multifrequency electrical impedance-based system (MFEIBS) for clinical imaging: design and performance evaluation
Published in Journal of Medical Engineering & Technology, 2018
Gurmeet Singh, Sneh Anand, Brejesh Lall, Anurag Srivastava, Vaneet Singh
Using the number of tests, the performance of EIT system is validated after reducing the sources of errors. These include common mode rejection ratio (CMRR), signal to noise ratio (SNR) and accuracy test using resistors and capacitors of known value with ±1% tolerance and saline water tank. These performance parameters are summarised in Table 2 by giving mean, minimum and maximum values. CMRR gives the information of rejecting the common mode signal to both the electrodes in the differential amplifier. It is the ratio of common mode gain to differential gain. Moreover, the CMRR more is the rejection of noise. Variation of CMRR with the frequency is as shown in Figure 12. Maximum value of CMRR is 85 dB. CMRR is calculated as the same method given in Figure 13 by Yerworth et al. [38,39]. Different parameters responsible for common mode errors like finite common mode rejection from instrumentation amplifier, imbalance in electrode impedance, relative position of current injection electrodes and voltage sensing electrodes was taken into account while measuring CMRR [40]. SNR gives the ratio of mean value to the standard deviation in output. Average and variance signals of the 1000 data frame each consisting of n values were calculated. SNR is calculated using cylinder tank phantom with saline water. A set of 15 readings of the surface potential is recorded from 100 Hz to 2 MHz using both opposite and neighbouring current injection protocols. SNR is calculated using the following equation: