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 0.18μm 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.
Highlights
Analog frequency filters are an important component of signal processing system
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
By analyzing the comparison table, it can be observed that the proposed filter structure holds certain advantages over the other similar designs and performs at par with other designs in terms of power dissipation, supply voltage, and total harmonic distortion, in addition to being the first truly mixedmode filter based on the voltage differencing buffered amplifier (VDBA)
Summary
Analog frequency filters are an important component of signal processing system. They are employed in instrumentation systems, communication systems, speech processing, sensor data preprocessing, data acquisition systems, etc. [1,2,3]. Reported VDBA-based universal biquadratic filters have three major limitations that severely curtail their application spectrum, which are: (a) non-availability of all five filter responses, (b) the employment of floating passive components, and (c) passive component matching constraints It can be inferred from the comparative study that out of the 30 designs available in the literature; only 15 can provide all five filter responses in either VM and CM mode [23,26,34,35,36,39,41,42,43,44,45,46,47,48,49,52]. If operation in saturation region is assumed and W/L ratio for transistors M1 and M2 are made identical the output current IZ of the OTA is given by Equation (2): The voltage follower forms the second stage of the VDBA designed using transistors M15–M21.
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