## 1 Introduction  
The current differencing transconductance amplifier (CDTA) is an active building block for current-mode signal processing applications [1, 2]. It is widely used in various applications, including universal filters [2, 3, 4, 5, 6], sinusoidal oscillators [7, 8, 9], capacitance multipliers [10, 11], precision rectifiers [12, 13], memristor emulators [14, 15, 16], and chaotic oscillators [17]. However, traditional CDTA circuits are not suitable for low-voltage, low-power applications because their design does not inherently support efficient operation under these conditions. In modern electronic systems, both analog and digital circuits increasingly require low-voltage, low-power operation [18, 19, 20].  
Several low-voltage, low-power CDTAs have been reported in the literature [21, 22, 23, 24, 25]. The circuit in [21] operates with a \(\pm\)0.6 V supply voltage and consumes 143 \(\upmu\)W of power using 0.18 \(\upmu\)m TSMC technology. In [22], a \(\pm\)1.4 V supply voltage is used, with a power consumption of 2.6 mW using 130 nm TSMC technology. The circuit in [23] operates with a \(\pm\)0.8 V supply voltage and demonstrates low power consumption using 0.18 \(\upmu\)m CMOS technology. Another design in [24] uses a \(\pm\)1 V supply voltage and consumes 0.1 mW of power using 0.18 \(\upmu\)m CMOS technology, while [25] operates with a 0.5 V supply voltage and consumes 1.05 \(\upmu\)W using 0.18 \(\upmu\)m CMOS technology.  
Universal filters provide five fundamental filtering functions, low-pass filter (LPF), high-pass filter (HPF), band-pass filter (BPF), band-stop filter (BSF), and all-pass filter (APF), within a single topology. These filters are extensively used in communication, control, electronics, and instrumentation systems. For example, they are employed in crossover networks for high-fidelity loudspeakers and for tone decoding in touch-tone telephones [26; 27]. Low-voltage, low-power universal filters are becoming increasingly important in biomedical systems [28]. In current-mode signal processing circuits, they offer several advantages, such as wide signal bandwidth and ease in adding and subtracting current signals. The ideal characteristics of current-mode filters include low input and high output impedance, no requirement for input signal matching, and no need for inverted input signals, thereby eliminating the need for additional circuitry. Several low-voltage, low-power current-mode universal filters have been proposed using various active devices, such as transconductance amplifiers [29; 30; 31] and voltage second-generation current conveyors (VCII) [32; 33]. In recent years, reducing the supply voltage and power consumption of active elements has become essential, particularly for wearable and biomedical applications [34; 35; 36; 37].  
This paper presents a low-voltage, low-power CDTA that utilizes the bulk-driven MOS transistor technique, operating in the weak inversion region, to achieve its low-voltage and low-power characteristics. To demonstrate the advantages of the proposed CDTA, it is applied in current-mode universal filters. The proposed filter provides both non-inverting and inverting transfer functions for LPF, HPF, BPF, BSF, and APF, with low input and high output impedances, electronic tuning capability, no component-matching requirements, and no inverted input signals. Additionally, the natural frequency of the filter can be electronically controlled.