*3.6.2. Bipolar configuration*

Bipolar configuration is used to acquire EMG signal using two EMG detecting surfaces with the help of a reference electrode. The signals from the two EMG surfaces are connected to a differential amplifier. The two detecting surfaces are placed only 1-2 cm from each other. The differential amplifier suppresses the common noise signals to both inputs and then amplifies the difference [5, 14]. The limitations of the monopolar configuration are catered for by this configuration. This is the most commonly used electrode configuration. The bipolar EMG electrode configuration is shown is Figure 13.

Signal Acquisition Using Surface EMG and Circuit Design Considerations for Robotic Prosthesis 439

role in hampering the recording of the EMG signal. For this purpose, the signal has to be

The noise frequencies contaminating the raw EMG signal can be high as well as low. Low frequency noise can be caused from amplifier DC offsets, sensor drift on skin and temperature fluctuations and can be removed using a high pass filter. High frequency noise can be caused from nerve conduction and high frequency interference from radio

In order to remove these high and low frequencies, high pass and low pass bio-filters will be

A high pass filter is used to remove low frequency component from a particular electrical signal. A term 'cut-off frequency', denoted by '*fc*', is the frequency below which all frequencies are eliminated. All frequencies above *fc* are carried forward. The frequency range where the filter response is '1' and the signals are transmitted is known as 'passband' region. On the contrary, the frequency range where the filter response is '0' and the signals are attenuated is known as 'stop band' region [18]. A high pass filter response is shown in

A high pass filter can be developed by using a resistor and a capacitor. This circuit will then be known as a CR circuit [20]. This circuit is a first order high pass filter. It is the simplest high pass filter possible. The high pass filtered signal is gathered across the resistor. The

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broadcasts, computers, cellular phones etc. and can be deleted using a low pass filter.

properly filtered, even after differential amplification [18, 19].

discussed in adequate detail in this section.

*4.1.1. High pass filter* 

**Figure 14.** A high pass filter response

The cut-off frequency of the high pass filter is given in Eq. 3.

filter is shown in Figure 15.

Figure 14.

**Figure 13.** Bipolar Configuration
