CMOS OTA based inductance, resistance simulator circuits and applications

In this study, employing different dual output operational transconductance amplifier structures (DO-OTA) as analog circuit building blocks, inductance and resistance simulation circuits are constructed and investigated. The circuits investigated in the frame of this thesis are intended to realize different applications employing these inductance and resistance simulators.The study reviews mainly circuits containing floating inductance simulators employing operational transconductance amplifiers (OTAs). The simulated inductance values can be controlled by adjusting the bias current of the OTA. The circuit performances are depicted through SPICE simulations, they show good agreement with theoretical results. Some applications as resonant circuit and inductance cancellation circuit are included to confirm the usability of proposed circuits. Current mode designs are owing the possibility to operate at higher frequencies compared to the voltage mode circuits employing op-amps. The current mode analogue circuits employing active elements such as operational transconductance amplifiers (OTAs), second generation current conveyor (CCII), dual output operational transconductance amplifiers (DO-OTAs), dual output second generation current conveyor (DO-CCIIs), four-terminal floating nullors (FTFNs), play an important role in the IC design, since these active elements exhibit greater linearity and wider bandwidth and wider dynamic range over the voltage mode counterparts. The resistance simulators can be implemented as floating and grounded resistors but the floating resistor is more convenient to use than the grounded resistor. The positive resistance simulator is required in the instrumentation systems, programmable amplifiers, filters, oscillators and etc. while the negative resistance simulator is very useful in various applications such as impedance matching, instrumentation system, cancelling resistance circuit, improving the quality factor of resonant circuit. In general, the resistance simulator is realized instead of the passive resistor to achieve low power consumption, it is easy to fabricate and can be electronically controlled so it is very suitable to use in the automatic control systems. The resistance simulators realized with CMOS technologies have been proposed in several works in the literature, unfortunately their supply voltages are quite high and they are only able to operate at low frequencies. In this study, classical DO-OTA, classical Arbel Goldminz and modified Arbel Goldminz circuits are examined and these structures are considered to be implemented with CMOS TSMC 0.18μ technology. Actively simulated grounded inductors find applications ranging from filter to oscillator design for cancellation of parasitic inductances. Many design possibilities are presented in the literature employing operational amplifiers, current conveyors, OTAs etc. as active elements. The actively simulated inductors can be classified due to the type or the number of active and passive elements employed. Further comparison can be made whether they realize lossy or lossless types. As mentioned earlier, operational amplifiers are important building blocks for analog circuit design. Unfortunately, their limited performance such as bandwidth, slew-rate etc. leads the analog designer to search other possibilites and other building blocks. As a result, new current-mode active building blocks such as operational transconductance amplifiers (OTA), second generation current conveyors (CCII), current-feedback op-amps (CFOA), four terminal floating nullors (FTFN), differential voltage current conveyor (DVCC), differential difference current conveyor (DDCC), third-generation current conveyor (CCIII), dual X current conveyors (DXCCII), current controlled current conveyors (CCCII) etc. received considerable attention due to their larger dynamic range and wider bandwidth. Employing these new active elements for analog design and using CMOS technology for implementation the circuit designers obtained new possibilites to solve their problems. In this study, four CMOS realizations for the dual output operational transconductance amplifiers (DO-OTA) are given, DO-OTA is a very suitable active building blocks for current mode signal processing. Current differencing stage of the OTA element is realized using a differential current controlled current source and in the output stage, floating current sources are used to convert intermediate voltage of terminal to output currents. Due to the compactness of the circuit, it is capable of high-frequency operation and suitable for video signal processing applications. The DO-OTA element is used in a current mode anti aliasing seventh order video filter, so the resulting active filter exhibits the low sensitivity feature of its passive counterpart. The filter has 0.1 dB maximum pass band ripple as imposed by ITU video anti aliasing filter standard. SPICE simulation results of both the DO-OTA element and the seventh order elliptic filter are given. Simulation results are found in close agreement with theoretical results. In many signal processing applications, current mode circuits have become very good alternatives to voltage mode counterparts due to their relative large bandwidths. In current mode circuits, current source driven low impedance nodes carry current signals. That leads to higher frequency poles and results in high frequency operation. Moreover, since voltages are not essentially involved in signal processing, it is possible to design circuits at low supply voltages that are capable of high frequency operation. Because of those features, the interest towards current mode signal processing has steadily increased among many researchers and numerous current mode circuit structures are proposed. The four DO-OTA structures, namely classical DO-OTA-1, classical DO-OTA-2, classical Arbel Goldminz and modified Arbel Goldminz investigated in the frame of this thesis are compared with each other by means of ORCAD program, their strengths and weaknesses are specified from the view of point of features such as output resistance, noise, input and output swing range, frequency range, total harmonic distortion etc. so that the results in the frame of this work can be used to enlight the design considerations depending the application area. The thesis is organized as follows: After a brief introduction section covering the existing literature and describing the purpose of the thesis, Section 2 on CMOS OTA structures gives information about DO-OTA, Arbel Goldminz and modified Arbel Goldminz structures including circuit characteristics. Section 3 describes resistance simulation circuits employing OTA structures, followed by Section 4 on inductance simulators. Section 5 reflects R-L simulation circuits with applications. Section 6 gives filter applications employing the investigated simulators. Finally, Section 7 gives conclusions and comparative performance analysis.