Design of Electronically Controllable Multifunction Active Filter with Amplitude Controllability Using Two Commercially Available ICs

Abstract

In this contribution, the design and analysis of an active multifunction biquad filter that provides five voltage-mode filtering configurations in the same core filtering circuit are presented. The design emphasizes using the commercially available ICs, LT1228, which are easy for off-the-shelf implementation and cheaper compared with the chip implementation. The proposed multifunction filter is realized from two commercial LT1228 ICs as the active function block, combined with five passive elements (three resistors and two capacitors) with three input voltage nodes and a single output voltage node. The following advantages are given for this design: (i) it provides high-pass (HP), low-pass (LP), band-stop (BS), band-pass (BP), and all-pass (AP) filtering functions; (ii) orthogonal and electronic tuning of the natural frequency ω 0 and bandwidth (the quality factor: Q); (iii) output voltage node of the proposed circuit is low impedance; (iv) passband voltage gain is controllable; and (v) matching condition and extra double gain voltage-mode amplifier are not required. The effect of the parasitic element in LT1228 on the filter performance is analyzed and included to strengthen the design idea. The PSpice simulation results using LT1228 with ±5 V and the experimental results tested from the hardware implementation are given to prove the validity of the designed multifunction filter.

Two New and Improved Electronically Adjustable Voltage-Mode Multifunction Biquadratic Filters With Independent Control of Band-Pass, High-Pass, and Low-Pass/Regular Notch Filter Gains

“…ABBs have been published in the open technical literature [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]. VM multifunction biquadratic filters composed of various highperformance ABBs, such as voltage differencing buffered amplifier (VDBA) [23], [24], [25], [26], current feedback amplifier (CFA) [27], [28], [29], [30], [31], [32], differential difference transconductance amplifier (DDTA) [33], voltage differencing differential difference amplifier (VDDDA) [34], voltage differencing differential input buffered amplifier (VD-DIBA) [35], [36], operational transconductance amplifier (OTA) [37], [38], [39], and LT1228 [40], [41], [42], [43], [44], can be found in the open literature and play an important role in various electronic systems. Biquadratic filters generally implement LP, BP, HP, RN and all-pass (AP) filtering ...…”

“…The focus of this study is the simultaneous implementation of LP, BP, HP and LPN/RN filters from the same configuration, providing independent control of their filter gains. Reviewing the technical literature published in [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], and [43], these circuits suffer from one or more of the following drawbacks.…”

“…1) Lack of high input impedance for the cascaded input voltage signals [42]. 2) Lack of three low output impedances for the cascaded output voltage signals [20], [23], [24], [25], [26], [35], [36], [37], [38], [39], [40], [41], [42]. 3) No orthogonal and electronic tunability of the ω o and Q [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [35], [36], [41].…”

“…4) No Q-value independent and electronic controllability [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [35], [36], [41]. 5) Inability to provide six filtering responses simultaneously in a single topology [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [35], [36], [37], [38], [39], [40], [41], [42], [43]. 6) Inability to provide independent gain control of BP, HP, and LPN/RN filters [20], [21], [22], [23], [24], [25], [26], [27], [28],…”

Synthesis of High-Input Impedance Electronically Tunable Voltage-Mode Second-Order Low-Pass, Band-Pass, and High-Pass Filters Based on LT1228 Integrated Circuits

“…Due to its wide transconductance amplifier, high voltage-gain, large signal bandwidth, wide supply voltage, high accuracy, and high drive capability, the commercially available LT1228 IC is an interesting electronically tunable active component suitable for many circuit designs. As a result, many active VM second-order filters, oscillators, inductance simulators, and wave generators based on the attractive commercial LT1228 ICs were proposed in the literature [ 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ]. The LT1228 implements gain-controlled through a transconductance g m at the front end and a CFA at the back end, and combines these two amplifiers into an 8-pin package [ 49 ].…”