# Single EX-CCCII-Based First-Order Versatile Active Filter
## 1 Introduction  
Current-mode circuits are usually implemented using second-generation current conveyors (CCII) [1] as they offer a better dynamic range, bandwidth, and linearity compared to operational amplifiers (op-amp) [2; 3]. The conventional CCII is a single-end active block, it has \(\gamma\), \(\kappa\)-, and z-terminals, and usually requires many passive components to realize applications. In order to overcome these limitations and extend the range of the CCII, other functional blocks have been proposed. Some examples are the differential difference current conveyor (DDCC) [4] or the fully differential second-generation current conveyor (FDCCII) [5], which enables arithmetic operations. Further examples include the dual-x second-generation current conveyor (DX-CCII) [6] and the extra-x second-generation current conveyor (EX-CCII) [7], which both provide multiple x- and z-terminals. The extra-x current controlled second-generation current conveyor (EX-CCCII) has also been proposed [8]. Compared to the EX-CCCII, the EX-CCCII considers the intrinsic resistance at the x-terminal, which can be electronically controlled by a bias current. This is advantageous in applications because it can be used as a tuning parameter. Therefore, EX-CCCII-based circuits are able to be free of passive resistors while offering the possibility of electronic tuning. First-order filters are fundamental circuits used to construct biquad-based odd high-order filters, multiphase sinusoidal oscillators, and quadrature oscillators [9; 10; 11]. The first-order filter is a single pole frequency filter; therefore, three first-order filters can berealized: the low-pass filter (LPF), high-pass filter (HPF), and all-pass filter (APF). Many first-order filters are available in the literature [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38]. Depending on the input and output signals, these first-order filters can be categorized into three operation modes: voltage-mode (VM) [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22], current-mode (CM) [23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38], and mixed-mode (MM) [39; 40; 41; 42; 43; 44; 45; 46; 47; 48]. The filter structures in [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38] can realize the LPF, HPF, and APF in the same topology. This work focuses on a current-mode first-order filter that offers the LPF, HPF, and APF in a single topology. The CM first-order filters in [23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38] use various active elements, such as CFTAs (current follower transconductance amplifiers) [23], current amplifiers [24], current conveyors [25; 26; 27; 28; 29; 30; 31; 32; 34; 38], CFOAs (current feedback operational amplifiers) [30], CBTAs (current backward transconductance amplifiers) [31], CCTAs (current conveyor transconductance amplifiers) [33; 36], CDTAs (current differencing transconductance amplifiers) [35], and OTAs (operational transconductance amplifiers) [37]. The filter structures in [23; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38] use only one active element, but these filters have some disadvantages: (i) they do not provide both non-inverting and inverting transfer functions of the LPF, HPF, and APF [25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36], which may lead to a need for additional non-inverting/inverting amplifiers for applications; (ii) they do not enable electronic tuning capabilities [26], making it difficult to compensate for the filter cut-off frequency when circuit parameters deviate due to temperature changes; and (iii) they use a floating capacitor [32], which is not ideal for integrated circuits because it is not easy to compensate for the stray capacitance. Filters that can implement the VM, CM, transimpedance-mode (TIM), and transadmittance-mode (TAM) from the same configuration are usually classified as universal mixed-mode filters.