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In this paper, a new current differencing cascaded transconductance amplifier (CDCTA) is presented. The CDCTA circuit consists of a current differencing unit and n cascaded highly linear voltage-controlled transconductance amplifiers, and it possesses wide bandwidth and lineartunable feature. Based on this CDCTA, a systematic design method generating current-mode (CM) multiple-loop feedback filter is proposed. By altering the parameters of the design matrix, multiple nth-order CM all-pole low pass filters structures can be synthesized without changing internal circuit. The nth-order filters have low complexity and meet the requirement of no active and passive element matching conditions as adopting only a single CDCTA and n grounded capacitors. Furthermore, the frequency of the nth-order filters can be linearly tuned by the bias voltage. A fourth-order Butterworth filter is designed as an example, and its Cadence simulation results have good agreement with the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, a new fourth-order complex (polyphase) filter is realized with the leapfrog structure. The proposed filter is based on the first-order stage using multi-output current differencing transconductance amplifiers (MOCDTAs). The design procedures for the realization of the first-order stage and fourth-order leapfrog polyphase filter are presented. In the procedures, the signal flow diagrams are also presented. The proposed design using MOCDTA simplifies the circuit of the current-mode leapfrog complex filter, where there are no resistors and with minimum number of active components. Besides, its centre frequency and bandwidth could be electrically tunable independently. The centre frequency of the proposed filter could be adjusted from 20 to 80 MHz, and its bandwidth could be more than 20 MHz. With ± 1.25 V supply, two examples of the proposed filter are introduced. Their bandwidths are from 46.1 to 68.5 MHz and from 22.3 to 48.4 MHz, respectively. Their image rejection ratios could be more than 59 and 39 dB, respectively. Meanwhile, both the IIP3s are over 18 dBm. The theoretical results are demonstrated by using SPECTRE simulation in CHRT 0.18 μm standard complementary metal oxide semiconductor (CMOS) process. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Abstract: This letter presents a single CDTA (Current Differencing Transconductance Amplifier)-based current-mode quadrature oscillator (QO). The proposed circuit structure is very simple, which only consists of one CDTA, one resistor and two capacitors, and it is easy for monolithic integration. The oscillation frequency of the QO can be electronically controlled by the bias current of the CDTA. Moreover, the oscillator can provide two quadrature current outputs. PSPICE simulation results are provided to verify all the theoretical analysis. [Copyright &y& Elsevier]