Single Commercially Available IC-Based Electronically Controllable Voltage-Mode First-Order Multifunction Filter with Complete Standard Functions and Low Output Impedance

Abstract

This paper presents the design of a voltage-mode three-input single-output multifunction first-order filter employing commercially available LT1228 IC for easy verification of the proposed circuit by laboratory measurements. The proposed filter is very simple, consisting of a single LT1228 as an active device with two resistors and one capacitor. The output voltage node is low impedance, resulting in an easy cascade-ability with other voltage-mode configurations. The proposed filter provides four filter responses: low-pass filter (LP), high-pass filter (HP), inverting all-pass filter (AP−), and non-inverting all-pass filter (AP+) in the same circuit configuration. The selection of output filter responses can be conducted without additional inverting or double gains, which is easy to be controlled by the digital method. The control of pole frequency and phase response can be conducted electronically through the bias current (IB). The matching condition during tuning the phase response with constant voltage gain is not required. Moreover, the pass-band voltage gain of the LP and HP functions can be controlled by adjusting the value of resistors without affecting the pole frequency and phase response. Additionally, the phase responses of the AP filters can be selected as both lagging or leading phase responses. The parasitic effects on the filtering performances were also analyzed and studied. The performances of the proposed filter were simulated and experimented with a ±5 V voltage supply. For the AP+ experimental result, the leading phase response for 1 kHz to 1 MHz frequency changed from 180 to 0 degrees. For the AP− experimental result, the lagging phase response for 1 kHz to 1 MHz frequency changed from 0 to −180 degrees. The design of the quadrature oscillator based on the proposed first-order filter is also included as an application example.

CFOA‐based simple mixed‐mode first‐order universal filter configurations

“…From Table 1, the following may be noted: The circuits of previous works 2,29–43 use more than one ABB, two ABBs 2,29–42 and three ABBs, 43 and, hence, do not belong to the class of single‐ABB‐based first‐order UAFs to which the circuits proposed in this article belong to. The single‐ABB‐based earlier works 3,10,12–14 use only a single ABB but realize a UAF only in CM, whereas other studies, 16–27 too, use only one ABB but realize an UAF only in VM. On the other hand, the single ABB configuration of Chaturvedi and Kumar 11 is in CM/TAM mode, whereas single ABB configuration of Maheshwari et al 15 and Singh et al 24 are in VM/TAM mode. None of the building blocks employed in previous works 3–24,26,27 are yet available as off‐the‐shelf ICs. The circuits of previous studies 5,14,20–22,24–27 do not employ a grounded capacitor. The UAFs in previous works, 5,16–19,21,23–25,27 do not have the appropriate Z in or Z out to enable cascadability. The only other earlier work which is based upon the use of a commercially available IC (namely, the LT1228 comprising an OTA followed by a CFOA) also realizes only VM UAF and does not employ a grounded capacitor. …”

“…A brief overview of earlier published first‐order UAFs is now in order. However, in order to keep the overview of the earlier works 2–43 as brief as possible, we have compiled the relevant data in tabular form as shown in Table 1.…”

“…ii. The single-ABB-based earlier works 3,10,[12][13][14] use only a single ABB but realize a UAF only in CM, whereas other studies, [16][17][18][19][20][21][22][23][24][25][26][27] too, use only one ABB but realize an UAF only in VM. On the other hand, the single ABB configuration of Chaturvedi and Kumar 11 is in CM/TAM mode, whereas single ABB configuration of Maheshwari et al 15 and Singh et al 24 are in VM/TAM mode.…”

“…iv. The circuits of previous studies 5,14,[20][21][22][24][25][26][27] do not employ a grounded capacitor. v. The UAFs in previous works, 5,[16][17][18][19]21,[23][24][25]27 do not have the appropriate Z in or Z out to enable cascadability.…”

Fully Differential Current-Mode Configuration for the Realization of First-Order Filters with Ease of Cascadability

“…A first-order universal filter realizes high-pass (HP), low-pass (LP), and AP configurations in the same circuit. A large part of technical documentation [4][5][6][7][8][9][10][11] is focused on single-ended first-order filters, due to their design simplicity and implementation. However, single-ended circuits have several drawbacks in a few specific ambient conditions.…”