Instrumentation amplifiers using operational transconductance amplifiers

Instrumentation amplifier circuits using operational transconductance amplifiers (OTAs) as active circuit elements are proposed in this paper. Two new instrumentation amplifier circuits have been described and experimentally verified, where the first circuit comprises four OTAs and five resistors and the second circuit comprises two OTAs and three resistors.     

Universal current mode biquad using a single CFOA

Because of their several advantages over the traditional voltage mode op-amp, current feedback op-amps (CFOAs) have attracted prominent attention as alternative building blocks for biquad filter realization. Previously known universal current mode (CM) biquads (i.e. those capable of realizing all five generic filter functions, namely low-pass, band-pass, high-pass, notch and all-pass) are realizable with CFOAs but require two to nine CFOAs. Although a few dual-function/three-function single-CFOA-based CM circuits have appeared in the literature, no single-CFOA-based canonic universal CM biquad with explicit CM output has been reported until now. This paper presents such a circuit. The workability of the proposed circuit has been confirmed by PSPICE simulations based upon AD844-type CFOAs.     

Versatile active-only biquad circuits with loss-less and lossy integrators

This paper presents a realization of voltage-mode and current-mode active-only biquad circuits with a two-integrator loop-structure. The circuits are constructed solely with operational amplifiers (OAs) and operational transconductance amplifiers (OTAs). The biquad circuits can realize the multiple circuit transfer functions, and the circuit parameters can be tuned orthogonally through adjusting the transconductance gains of the OTAs. Also, these biquad circuits enjoy very low sensitivities with respect to the circuit active elements. Some examples are given together with simulated results by PSPICE.

The circuit configurations are very suitable for implementation on both bipolar and CMOS technologies.     

OTA-based monostable multivibrators with current tuning properties

This paper presents two new monostable multivibrator circuits based on operational transconductance amplifiers (OTAs). Both configurations use two OTAs with a few passive components. The first circuit is operated under the positive-edge triggering mode, and the second one is a negative-edge triggering mode design. The width and height of the output pulse are tunable via the bias current of OTAs or an external resistor. The proposed monostable multivibrators are more compact compared to the existing designs. In order to verify the feasibility of the presented circuits, prototypes are implemented, using commercial ICs and discrete components. In addition, the circuit principles are described and analyzed in detail. Experimental results are close to the theoretical analysis.     

Current mode filters with reduced complexity using a single EX-CCCII

In this paper an active element Extra-X current controlled conveyor (EX-CCCII) is used to reduce the complexity of some existing circuits. Two second-order current-mode biquadratic filter circuits are proposed, each using a single active element and two grounded capacitors. The first circuit is three input single output (TISO) and the second one is single input three outputs (SITO) biquadratic filter. The First circuit can realize all the standard filter transfer functions, while the second circuit can realize LP, BP and HP responses. The study of non-idealities and parasitics of the active element and their effects on transfer functions is carried out. The new circuits are found to be simpler than the earlier ones in terms of number of transistors. The functionality of the proposed biquadratic filters is verified through detailed PSPICE simulations using 0.25 µm TSMC CMOS technology parameters.     

Novel First-Order and Second-Order Current-Mode Filters Using Multiple-Output Operational Transconductance Amplifiers

In this paper, a general structure using dual-output operational transconductance amplifiers (OTAs) is explored to derive new first-order and second-order multi-function filters using OTAs with multiple current outputs and with and without grounded capacitors. Two first-order all-pass filters that have been obtained are presented, together with an analysis of nonidealities of OTAs, viz., finite bandwidth and parasitic output and input resistance and capacitance. Second-order multi-function filters obtained by using OTA-C simulated inductances in the proposed general structure are also presented. The realization of quadrature oscillator using the proposed first-order all-pass networks is also considered. Detailed analysis of nonideal frequency performance of the OTAs as well as finite output and input impedances is presented. SPICE simulation results are also given for the proposed circuits.     

On the systematic synthesis of OTA-based Wien oscillators

A NAM expansion method for systematic synthesis of OTA-based Wien oscillators is given. Moreover, the NAM expansion method for four different classes of the oscillators is considered. The class I oscillators employ three OTAs, the class II oscillators employ four OTAs, the class III oscillators employ five OTAs, and the class IV oscillators employ six OTAs. Each class has 32 different forms, resulting in 128 Wien oscillators using OTAs. Having used grounded capacitors, the circuits are easy to be integrated and their parameters can be tuned electronically through tuning bias currents of the OTAs. The MULTISIM simulation results have been included to support the generation method.     

Design of high-order elliptic filter from a versatile mode generic OTA-C structure

A new synthesis methodology for high-order versatile mode programmable Operational transconductance amplifier and capacitor (OTA-C) generic filter structure is proposed. The structure fulfills the three main criteria of high frequency operation i.e it uses (1) less number of components (2) only single ended input OTAs (3) only grounded capacitors. Any nth order transfer function can be realised from it. Elliptic filter is designed from the generic structure using optimisation technique to reduce the number of OTAs. SPICE simulation with BSIM level 53 model and 0.13 μm process confirms the theoretical analysis. Frequency response of third-order and fourth-order elliptic filter is shown as representative set of simulated result. Sensitivity and non-ideal effect of the designed filter are studied.     

Active only integrator and differentiator with tunable time constants

In this paper new active only current-mode integrator and differentiator with electronically tunable time constants are described. They are composed of one operational amplifier (OA) and two operational transconductance amplifiers (OTAs), and are suitable for monolithic implementation either with CMOS or bipolar technologies. No realizability conditions are imposed for the proposed circuits and all of the active sensitivities are low. The performances of the circuits are demonstrated on the PSPICE platform.     

Novel multiple function analog filter structures and a dual-mode multifunction filter

This paper reports three multi-function filters each of which realizes at least three basic functions without any external passive elements. Depending on the circuit, from one to four operational transconductance amplifiers (OTAs), and two operational amplifiers (OPAMPs) are employed. All three circuits are transimpedance-mode circuits; one of them can also operate as a current-mode filter. Therefore this filter represents a dual-mode, multifunction filter. The presented theory is verified with macro models in simulation program with integrated circuit emphasis (SPICE) simulations and post layout simulations, which are carried out with parasitics extracted from the layouts of the filter chips.     

A new electronically tunable phase shifter employing current-controlled current conveyors

A new canonical current-mode (CM) filter topology is presented. It realizes first-order allpass filtering functions using two dual-output current-controlled current conveyors (DO-CCCII) and a single capacitor. The topology gives both inverting and non-inverting types of these filters. Owing to electronically tunability properties of the CCCII, phase response of the circuit can be controlled by an external control current. Realization of the allpass filter imposes no matching condition. All outputs of the filters exhibit high output impedances so that this property makes the circuits very attractive from the viewpoint of cascading in current mode. The theoretical results are verified with PSPICE simulations using a BJT realization of CCCII.     

Current mode multifunction filter using two CDBAs

This paper presents a cascadable current-mode (CM) multifunction biquadratic filter. The proposed circuit realizes all five different filter transfer functions employing only two current differencing buffered amplifiers (CDBAs), while previously reported CM multifunction filters require more CDBAs and more passive component count for the same number of filter transfer function realizations. Examples for different filter transfer functions are given along with the results of circuit simulations. It is shown that theoretical and simulation results are in good agreement.     

A Novel CMOS OTA Based on Body-Driven MOSFETs and its Applications in OTA-C Filters

The operational transconductance amplifier (OTA) is one of the most significant building-blocks in integrated continuous-time filters. Traditional OTAs suffer linearity reduction as a result of the MOSFET scaling trend. In this paper, a body-driven (BD) CMOS triode-based fully balanced OTA is proposed to achieve low distortion and linear frequency tuning. In contrast to the gate-driven based OTAs (that have the tradeoff of input and tuning range), BD-based OTAs operate under a wide input range over a large tuning interval. Common-mode (CM) feedforward and CM feedback schemes have been developed so that the CM voltage varies only 7 mV over a tuning range of 1.2 V = Vtune = 1.58 V. Using the 0.18-mum N-well CMOS process, a third-order elliptic low-pass filter is implemented with the aid of the proposed OTA. The total harmonic distortion ( is -45 dB for 0.8-V peak-peak (Vpp) fully differential input signals. A dynamic range of 45 dB is obtained with the OTA's noise integrated over 1 MHz.     

Partial positive feedback for gain enhancement of low-power CMOS otas

Four circuit schemes that use partial positive feedback for gain enhancement in CMOS OTAs are examined. These circuit schemes are classified as type I and type II circuits. Type I circuits use a differential input pair with positive feedback and type II circuits use a active load with positive feedback. As the primary emphasis of these circuits is for micropower operation, the circuits have been examined in detail in the subthreshold region. A comparison of the primary characteristics of these circuits together with simulation results are presented. It is shown that partial positive feedback is a viable technique to increase the gain and the bandwidth of CMOS OTAs. Without any increase in power, a 20 dB increase in gain and a 5X improvement in bandwidth is feasible.     

New high-order filter structures using only single-ended-input OTAs and grounded capacitors

Despite the wealth of literature on operational transconductance amplifier (OTA)-C filters, the synthesis of high-order filter characteristics is still an active topic. In this paper the realization of voltage transfer functions based on canonical current-mode follow-the-leader-feedback (FLF) OTA-C structures are investigated. Two new structures are presented, which use only single-ended-input OTAs and grounded capacitors. The first structure has a single voltage input and multiple voltage outputs taken from different nodes, which enables it to provide simultaneous outputs of different filter functions. The second structure has a single voltage output and single voltage input distributed to different circuit nodes for a universal realization. The authors not only propose such filter structures, but also show how analytical synthesis can be used to produce filter circuits that have less active elements than those recently reported voltage-mode structures which are based on differential-input OTAs. This represents another attractive feature from chip area, and power consumption point of view. Simulation results verifying the theoretical analysis of the proposed filter structure are included.     

Transverse and longitudinal mode control in semiconductor injection lasers

Mechanisms which determine the oscillating transverse and longitudinal modes in semiconductor injection lasers are discussed in this paper. The analysis is based on the semiclassical method in which the optical field is represented by Maxwell equations and the lasing phenomenon is analyzed quantum mechanically using the density matrix formalism. Guided modes are classified by the relation between refractive index and gain-loss differences at the boundaries of the active region as normal guided mode (index guiding), active-guided mode (gain guiding), and leaky mode (anti-index guiding). The guiding loss and cutoff conditions are given for these modes. The optimum range to obtain stable fundamental transverse mode operation is discussed with respect to several guiding factors, such as width of active region, the refractive index difference, and gain-loss differences at the boundaries of the active region. Longitudinal mode behavior is discussed in terms of electron transition mechanism in semiconductor crystals. The relaxation effect of the electron wave is introduced in this model. Profiles of the saturated gain and the spatial diffusion of the electron are related to this relaxation effect. Mode competition phenomena are analyzed, and a strong gain suppression among the longitudinal modes is shown to be as an intrinsic property of semiconductor lasers. The possibility of obtaining single longitudinal mode operation is postulated. Physical influences for stable single longitudinal mode operation are discussed in terms of transverse mode control (or stripe structure), spontaneous emission, threshold current level, impurity concentration in the active region, and direct modulation. Some experimental results are also given to support these analyses.     

Novel Canonic Current Mode DDCC Based SRCO Synthesized Using a Genetic Algorithm

A survey of the technical literature reveals that synthesis of Current Mode (CM) oscillators using single active building block (ABB) requires an additional identical or complementary current terminal to sense and take out the current output. The topologies of these oscillators are essentially based on the current mode approach. They use a Voltage Controlled Voltage Source (VCVS) and two current terminals to implement the CM oscillator. In the present paper, a novel DDCC (Differential Difference Current Conveyor, introduced in Chiu et al. (IEE Proc., Circuits, Devices, Syst., vol. 143, no. 2, pp. 91–96, 1996)) based canonic CM Single-Resistor Controlled Oscillator (SRCO) is presented, which uses a VCVS and a single current terminal to take out the output. Earlier, authors used DDCCC (Differential Difference Complementary Current conveyor), DVCCC (Differential Voltage Complementary Current Conveyor) to implement CM oscillators and hypothesized the requirement of an additional current terminal for the output. The synthesis of present topology indicates that DDCC is a versatile building block to implement canonic CM SRCOs and doesn't need any additional current terminal. This topology was synthesized using an innovative genetic algorithm. Spice simulations have been included and they verify theoretical results.     

Programmable capacitance scaling scheme based on operational transconductance amplifiers

A new programmable capacitance scaling scheme based on the utilisation of two tunable operational transconductance amplifiers (OTAs) is presented. The capability of the OTAs allows tunable positive/negative capacitance scaling factors. The scheme has been verified with simulations and experimentally using commercial bipolar OTAs and can be implemented in CMOS technology.     

Active mode leakage reduction using fine-grained forward body biasing strategy

Leakage power minimization has become an important issue with technology scaling. Variable threshold voltage schemes have become popular for standby power reduction. In this work we look at another emerging aspect of this potent problem which is leakage power reduction in active mode of operation. In gate level circuits, a large number of gates are not switching in active mode at any given point in time but nevertheless are consuming leakage power. We propose a fine-grained forward body biasing (FBB) scheme for active mode leakage power reduction in gate level circuits without any delay penalty. Our results show that our optimal polynomial time FBB allocation algorithm results in 70.2% reduction in leakage currents. We also present an exact standard-cell placement driven FBB allocation algorithm that effectively reduces the area penalty using the post-placement area slack and results in 56.5%, 62.8% and 66.1% reduction in leakage currents for 0%, 4% and 8% area slack, respectively. Furthermore, we present a heuristic to solve the standard-cell placement driven FBB allocation problem that is computationally efficient and results in leakage within 2% of that from the exact formulation.     

Electronically tunable high gain current-mode instrumentation amplifier

A new design for electronically tunable current mode (CM) instrumentation amplifier (IA) is presented in this paper. It employs Modified Z copy Current Differencing Transconductance Amplifier (MZC-CDTA) along with a resistor. The gain of the proposed CM IA is controlled by a single resistor and can theoretically approach infinite value. Electronic tuning feature is augmented by using a MOS based resistor. The functionality is verified through simulations on Cadence Virtuoso using TowerJazz’s 180 nm Technology Node and performance against PVT variations is also examined. Feasibility of on-chip implementation is confirmed by the post-layout simulations carried out.