Current Differencing Cascaded Transconductance Amplifier (CDCTA) and Its Applications on Current-Mode n th-Order Filters
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Current Differencing Cascaded Transconductance Amplifier (CDCTA) and Its Applications on Current-Mode nth-Order Filters Jun Xu · Chunhua Wang · Jie Jin
Received: 12 September 2012 / Revised: 31 January 2013 © Springer Science+Business Media New York 2013
Abstract In this paper, a new active device, current differencing cascaded transconductance amplifier (CDCTA), has been presented. The proposed CDCTA simplifies the design of the current-mode filter circuit considerably, especially the design of high-order filter. Moreover, a current-mode nth-order filter based on the CDCTA is proposed in the paper. The proposed circuit, which adopts only an active component and n grounded capacitors, contains minimal active component and passive one. It enjoys the simple configuration and is suitable for integrated circuit (IC) fabrication. PSpice simulations for current-mode third-order filter based on this structure have also been conducted, and the results are in good agreement with the theoretical analysis. The influences of the CDCTA non-idealities are also discussed. Keywords Current-mode · CDTA · CDCTA · nth-Order filter
1 Introduction Recently, a new current-mode active element, which is called a current differencing transconductance amplifier (CDTA) [3], has been introduced. This device with two current inputs and two kinds of current output is a synthesis of the well-known J. Xu () · C. Wang · J. Jin College of Information Science and Engineering, Hunan University, Changsha 410082, P.R. China e-mail: [email protected] C. Wang e-mail: [email protected] J. Jin e-mail: [email protected] J. Xu Unit 95316 of the People’s Liberation Army, Guangzhou 510900, P.R. China
Circuits Syst Signal Process
advantages of the CDBA [1] and OTA [8] to facilitate the implementation of currentmode analog signal processing. Its current input p, n terminals have extremely low input impedance and do not have parasitic capacitance, which expands circuit’s bandwidth greatly. Relative to some other IC based design circuits, such as OTA-based current-mode circuits (CA3080, BW = 2 MHz, Vpp = ±15 V), CCII [27] (AD844, BW = 20 MHz, VP P = ±20 V), OP (F741A, BW = 1.5 MHz, Vpp = ±15 V), circuits based on the CDTA device have some advantages in the number of active and passive elements, power consumption, bandwidth, etc. From the reported literature, some kinds of CDTA which are formed with a current differencing circuit and a transconductance circuit have been proposed in [4, 19, 33, 34, 46]. They are designed applying CMOS or bipolar technology and enjoy the simple structure. Meanwhile, CDTA has been widely used in current-mode signal processing circuit, such as inductance simulator circuits [13, 34], sinusoidal oscillator circuits [11, 12, 17, 22, 26, 38], and it is an especially promising choice for realizing the current-mode filters [2, 5–7, 9, 10, 15, 16, 18, 21, 24, 25, 27–32, 35, 36, 39, 41–47]. In general, most CDTA devices adopt conventional structure: a current differencing unit (CDU) followed by an operational transconductance
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