**3.6. EMG signal acquisition circuitry and configurations**

The EMG electrode placement has been elaborately explained under the previous heading. So, after properly understanding the target muscle profile, preparing the skin and positioning the EMG detecting surfaces, comes the EMG signal acquisition step.

EMG signal is acquired through differential amplification technique. The differential amplifier should have high input impedance and very low output impedance. Ideally, a differential amplifier has infinite input and zero output impedance [17].

Differential amplification is achieved with the help of an instrumentation amplifier for high input impedance. A classic three amplifier instrumentation amplifier is shown in Figure 11.

The instrumentation amplifier carries out differential amplification by subtracting the voltages V1 and V2. This way, the noise signal which is common at V1 and V2 (electrode inputs) e.g. power line interference etc. are eliminated. The tendency of a differential amplification to reject signals common to both inputs is determined by common mode rejection ratio (CMRR). A CMRR of 90 dB is enough for elimination of common signals for instrumentation amplifiers, but latest technology, even though expensive, provides us with a CMRR of 120 dB. But there are reasons for not pushing the CMRR to the limit, as the electrical noise detected by the electrodes may not be in phase [15]. The gain for the instrumentation amplifier can be set using a single resistor (Rgain). The gain equation and output equation of the instrumentation amplifier is given in Eq. 1 and 2.

Signal Acquisition Using Surface EMG and Circuit Design Considerations for Robotic Prosthesis 437

$$Gain = \left(1 + \frac{2R1}{Rgain}\right) \frac{R3}{R2} \tag{1}$$

$$\text{Vout} = (V2 - V1) \times Gain \tag{2}$$

A small gain of 5 or 6 is recommended for signal acquisition. Extensive amplification will be carried out in further steps. The placement of the EMG detecting surfaces can be done through three different configurations: monopolar, bipolar and multipolar.

**Figure 11.** A Three Amplifier Instrumentation Amplifier

#### *3.6.1. Monopolar configuration*

Computational Intelligence in Electromyography Analysis – 436 A Perspective on Current Applications and Future Challenges

**Figure 10.** EMG Spectrum and noise influence on this spectrum [16]

**3.6. EMG signal acquisition circuitry and configurations** 

The EMG electrode placement has been elaborately explained under the previous heading. So, after properly understanding the target muscle profile, preparing the skin and

EMG signal is acquired through differential amplification technique. The differential amplifier should have high input impedance and very low output impedance. Ideally, a

Differential amplification is achieved with the help of an instrumentation amplifier for high input impedance. A classic three amplifier instrumentation amplifier is shown in Figure 11. The instrumentation amplifier carries out differential amplification by subtracting the voltages V1 and V2. This way, the noise signal which is common at V1 and V2 (electrode inputs) e.g. power line interference etc. are eliminated. The tendency of a differential amplification to reject signals common to both inputs is determined by common mode rejection ratio (CMRR). A CMRR of 90 dB is enough for elimination of common signals for instrumentation amplifiers, but latest technology, even though expensive, provides us with a CMRR of 120 dB. But there are reasons for not pushing the CMRR to the limit, as the electrical noise detected by the electrodes may not be in phase [15]. The gain for the instrumentation amplifier can be set using a single resistor (Rgain). The gain equation and

positioning the EMG detecting surfaces, comes the EMG signal acquisition step.

differential amplifier has infinite input and zero output impedance [17].

output equation of the instrumentation amplifier is given in Eq. 1 and 2.

The monopolar configuration is implemented using only a single electrode on the skin with respect to a reference electrode as shown in Figure 12. This method is used because of its simplicity, but is strictly not recommended as it detects all the electrical signals in the vicinity of the detecting surface [5, 14].

**Figure 12.** Monopolar signal acquisition technique
