# 0.5-V High-Order Universal Filter for Bio-Signal Processing Applications
###### Abstract  
In this paper, a novel multiple-input operational transconductance amplifier (MIOTA) is proposed. The MI-OTA can be obtained by using the multiple-input bulk-driven MOS transistor (MIBD MOST) technique. The circuit structure is simple, can operate with a supply voltage of 0.5 V, and consumes 937 pW at a current setting of 625 pA. The proposed MI-OTA was used to implement a high-order multiple-input voltage-mode universal filter. The proposed filter can provide non-inverting and inverting low-pass, high-pass, band-pass, band-stop, and all-pass transfer functions to the same topology. In addition, it has a high input impedance and does not need any inverted input signals, so there is no additional buffering circuit. The proposed filter can be used for biological signal processing. The proposed MI-OTA and the second-order universal filter were simulated in Cadence using CMOS process parameters of 0.18 \(\upmu\)m from TSMC to verify the functionality and performance of the new structures. operational transconductance amplifier (OTA); high-order filter; multiple-input MOS transistor (MI MOST); bulk-driven technique; low-power +
Footnote †: journal: Applied sciences  
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In Figure 1, the preamplifier amplifies the low-amplitude signal, while the analog filter selects the frequency range and removes out-of-band noise. The filtered analog signal is converted to digital form by an analog-to-digital converter (ADC) and then further processed by a central processing unit (CPU) block. In an analog filter, a low-pass filter is typically used to select the frequency range and remove out-of-band noise [2]. A band-pass filter is typically used to select the desired frequency band and reduce out-of-band noise [3]. A notch/low-pass notch filter is typically used to suppress 50/60 Hz power line interference [4]. In addition, an all-pass filter can be used in hearing aids [5]. Thus, universal filters can be used in biomedical systems, which can realize low-pass filters (LPF), band-pass filters (BPF), band-stop filters (BSF), and all-pass filters (APF). Many active filters are available in the open literature for various applications in biomedical systems [3; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19]. First-order filters are presented in [6; 7; 8], second-order filters in [9; 10; 11; 12; 13], and third-order filters in [14; 15; 16]. Fourth-order filters are presented in [3; 17], and fifth-order filters are presented in [19; 20; 21; 22]. Sixth-order filters are presented in [23; 24; 25; 26], and ninth-order filters are presented in [27]. In other words, different biomedical applications require filters of different orders depending on the specific bio-signal characteristics and the type of noise or artifacts present. Many versatile high-order filters based on various active devices are available in the literature [28; 29; 30; 31]. The filters in [28; 29; 30; 31; 32] use current conveyors, while the filter in [33] uses current feedback operational amplifiers (CFOA). However, filters based on these active elements lack electronic tuning capability and require many passive resistors. Filters using current-controlled current conveyors in [34], operational transconductance amplifiers (OTA) [35; 36; 37; 38; 39; 40] provide electronic tuning capability that can easily compensate for natural frequency when it is affected by process and temperature variations. The high-order structures in [37; 38; 39; 40] consume low power and provide variant filtering functions, i.e., LPF, HPF, and BPF. In this paper, a high-order universal filter using multiple-input operational transconductance amplifiers (MI-OTA) is proposed. The multiple-input OTA can be realized by using the multiple-input bulk-driven MOS transistor (MIBD-MOST) technique. The MI-OTA can operate with a supply voltage of 0.5 V and consumes very low power by employing MOST operating in the subthreshold region.