AEU - International Journal of Electronics and Communications
LETTERDXCCII-based tunable gyrator
Introduction
Current-mode active elements offer the main advantages like greater linearity, lower power consumption and wider bandwidth over their voltage-mode counterparts [1]. Also, gyrators are very useful building blocks for synthetic simulation of inductances, frequency-dependent negative resistors or capacitance multipliers, which are widely used in design of continuous-time active filters and oscillators. Gyrators can be realised with current-mode active elements such as second-generation current conveyors (CCIIs) and current feedback amplifiers (CFAs) [1], [2], [3], [4] in which the gyration conductance values can be adjusted via two resistors. One of these circuits is the well-known Sedra–Smith gyrator [1], whereas the others were presented in [2], [3], [4].
Considering the tuning requirements of integrated continuous-time networks, an active gyrator employing current differencing buffered amplifier (CDBA) [5] has been proposed recently [6], whose gyration conductances are tunable via the MOSFETs of the MOS resistive circuits (MRCs) [7]. Although CDBA-based MOSFET-C circuits reduce the number of active and passive components and/or simplify the filter implementation significantly compared to their counterparts [7], [8], the MOSFETs of the MRCs require precise matching. Also, generalised gyrator implementation techniques using CCIIs and inverting current conveyors (ICCIIs) [9] have been reported recently [10].
The dual-X second-generation current conveyor (DXCCII—a new active device combining the main advantages of CCII and ICCII) avails tunability with aid of a triode MOSFET, while keeping large-signal linearity high. Its dual-X structure brings interesting features, which help reducing the number of elements used in a continuous-time filter [11]. Considering these advantages, a new active gyrator circuit is proposed in this work which employs only two DXCCIIs and two triode MOSFETs. Since only active devices are used and tuning is possible via triode MOSFETs, the new gyrator is very suitable for integrated tunable continuous-time filtering and device simulation applications.
Section snippets
Proposed gyrator circuit
DXCCII, whose symbol is given in Fig. 1a, is a combination of CCII and ICCII. A CMOS implementation of the DXCCII is shown in Fig. 1b (The principle of operation is explained in [11]). The terminal relationships of DXCCII can be given as [11],
It is well-known that usually voltage-controlled current sources (VCCSs) are employed to construct gyrators. A DXCCII-based VCCS can easily be realised by using a single triode MOSFET and a DXCCII [11]. Also, the
Simulation results and discussion
In order to reveal the functionality and performance of the DXCCII-based gyrator, SPICE simulations were performed for a new current-mode second-order filter (shown in Fig. 2b). The lowpass output current is available, whereas the bandpass output current is not. Nevertheless, a copy of can be obtained individually by repeating the MOSFET and its current source load of the output stage in the CMOS DXCCII shown in Fig. 1b. Routine analysis of this circuit yields
Conclusion
The proposed DXCCII-based gyrator is tunable and its large-signal linearity is high, thanks to the differential voltages across the triode MOSFETs. We proposed and simulated only a tunable current-mode biquad so as to reveal the advantages of the proposed gyrator. The biquad employs only two DXCCIIs, two triode MOSFETs and two grounded capacitors (less number of MOSFETs and capacitors compared to other approaches [6], [7], [8]). This reduces the parasitics and consumed chip area. The
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