## 1 Introduction  
The current differencing buffered amplifier (CDBA) was first introduced in [1]. This device features a positive current input (\(p\) terminal), a negative current input (\(n\) terminal), and a current output (\(z\) terminal). When an impedance is connected to the \(z\) terminal, the voltage at this terminal becomes equal to the voltage at the \(w\) terminal (the voltage output terminal). Therefore, this device offers advantageous features such as immunity to parasitic capacitance, wide bandwidth, and a high slew rate [2]. The CDBA has various applications, including universal filters [2, 3, 4, 5, 6, 7], high-order filters [1, 8, 9, 10, 11, 12, 13], sinusoidal oscillators [14, 15, 16, 17], inductance simulators [18, 19, 20, 21, 22], proportional-integral-derivative (PID) controllers [23], fractional-order multifunction filters [24, 25], and meminductor emulators [26, 27, 28]. Clearly, the CDBA is a compelling active building block for implementing analog circuits. However, these applications typically require a high supply voltage and consume a significant amount of power because the CDBA structures used are not designed for low-voltage, low-power operations. Although several high-performance CDBA structures have been reported in the literature [29, 30, 31, 32], they still suffer from the drawback of requiring high supply voltages. The CDBA in [7, 12] operates with a \(\pm\)1.25 V supply voltage, while the CDBA in [31, 10] operates with a \(\pm\)1 V supply voltage. The CDBA in [14] requires a \(\pm\)2 V supply voltage, and the one in [18] operates at \(\pm\)2.5 V. In [29], a \(\pm\)0.6 V supply voltage is used, consuming 565.25 \(\mu\)W of power. Another CDBA in [30] operates with a 0.7 V supply voltage, whereas the CDBA in [32] functions with a \(\pm\)0.8 V supply voltage. Currently, energy efficiency is becoming an increasingly crucial parameter for analog systems, driven by the growing demand for portable applications. It is well known that the threshold voltage of MOS transistors is the main obstacle in designing analog circuits to operate with a low supply voltage. Fortunately, this obstacle can be overcome using the bulk-driven MOS transistor (MOST) technique. This technique allows analog circuits to operate with a supply voltage as low as 0.5 V, even when the threshold voltage is also 0.5 V [33; 34; 35]. To achieve low-power circuits, a well-known technique involves the operation of MOS transistors in weak inversion. Low-pass filters can be applied to various systems, including telecommunications, control, and biomedical applications. They allow signals within a specific frequency range to pass while eliminating out-of-band noise. This work focuses on low-pass filters for applications in biomedical systems. Low-pass filters are widely used in biomedical applications, including electroencephalographic (EEG), electromyographic (EMG), and electrocardiographic (ECG) systems. Many low-pass filters suitable for these systems can be found in the literature; see, for example, [36; 37; 38; 39; 40; 41; 42; 43]. The filters in [36; 37; 38; 39; 40; 41] operate in voltage mode, whereas those in [42; 43] operate in current mode. This work focuses on current-mode filters due to their wide dynamic range, ease of signal addition and subtraction, and low supply voltage requirements [44; 45; 46]. Therefore, this paper proposes a low-voltage, low-power current differencing buffered amplifier (CDBA). The bulk-driven MOST technique is employed to achieve low supply voltage, while the MOST operating in weak inversion is used to reduce the power consumption of the proposed CDBA. The proposed CDBA is designed in the Cadence Virtuoso environment using 0.18 \(\mu\)m CMOS technology from TSMC. It operates at a supply voltage of 0.3 V and consumes 170 nW of power, with a bias current set to 10 nA. The proposed CDBA has been applied to a fully current-mode third-order low-pass filter with a cut-off frequency of approximately 110 Hz.