###### Abstract  
In this paper, a first-of-a-kind mixed-mode universal filter employing three VDBAs and three passive components, is proposed. The filter operates in all four modes and provides all five filter responses, namely voltage-mode (VM), current-mode (CM), trans-impedance-mode (TIM), or trans-admittance-mode (TAM). Additionally, the same filter topology can also work as a CM single-input-multi-output (SIMO) filter. A state-of-the-art comparison of various 'voltage differencing' variants of the voltage differencing buffered amplifier (VDBA)-based SIMO/MISO (single-input-multi-output/multi-input-single-output)-type biquad filters further highlight the significance of the presented research. In the proposed no passive component matching is required for generating the filter responses. The filter circuit also provides inbuilt tunability of the quality factor independent of the pole frequency. The non-ideal frequency dependent gain and component sensitivity analyses of the filter were also performed. The Silterra Malaysia 0.18 \(\upmu\)m process design kit (PDK) is employed to design and validated the proposed VDBA-based filter using the Cadence design software. The simulation results closely follow the theoretical predictions. To further verify the practical feasibility of the proposed filter, an experimental evaluation is also completed. The VDBA-based filter is implemented using off-the-shelf operational transconductance amplifiers Intersil CA3080, Texas Instruments LF356 op-amp, and Analog Devices AD844s. The filter is designed for a characteristic frequency of 100 kHz. The time and frequency domain measurement results indicate the proper functioning of the filter. a +
Footnote †: journal: Applied Sciences  
trans-admittance and trans-impedance stages are required to perform voltage to current (V-I) and I-V conversion. The mixed-mode filters will find application in such a scenario as it will perform the dual task of signal processing and signal conversion simultaneously. One such example is given in reference [4] of a three-way high-fidelity loudspeaker crossover network. The design of mixed-mode universal filters that can provide low-pass (LP), high-pass (HP), band-pass (BP), band-reject (BR), and all-pass (AP) filter responses in CM, VM, TAM, and TIM modes of operation are needed for the mixed signals system architecture [1; 2; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. The popular analog building blocks (ABBs) that are used in the design of active filters include operational transconductance amplifier (OTA) [5], second-generation current conveyor (CCII) [6], differential voltage current conveyor (DVCC) [16], extra current conveyor transconductance amplifier (EXCCTA) [21], differential difference current conveyor (DDCCII) [18], fully differential current conveyor (FDCCII) [15], current differencing buffer amplifier (CDBA) [3], etc. The voltage differencing buffered amplifier (VDBA) is another popular ABB that is very simple in design and versatile in realizing numerous applications [3; 22; 23; 24]. Various 'voltage differencing' variants of the VDBA are proposed, such as fully balanced voltage differencing buffered amplifier (FB-VDBA) [25], voltage differencing inverting buffered amplifier (VDIBA) [26; 27], fully balanced voltage differencing inverting buffered amplifier (FB-VDIBA) [28], or voltage differencing differential input buffered amplifier (VD-DIBA) [29]. In Tables 1 and 2, a comparative study is carried out to compare the state-of-the-art SIMO/MISO (single-input-multi-output/multi-input-single-output) voltage differencing unit (VDU)-based biquad filters [25; 26; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53] with here proposed designs. The comparison is made based on the following relevant criteria:  
1. Number of ABBs employed;
2. Count of passive components used;
3. A requirement of passive components matching condition;
4. Application of negative input for response generation;
5.