Output Operational Transconductance Amplifiers Research Articles

Programmable Universal Filter and Quadrature Oscillator Using Single Output Operational Transconductance Amplifiers

This paper presents a new programmable universal filter and quadrature oscillator based on single output operational transconductance amplifiers (OTAs). The proposed universal filter and quadrature oscillator can be achieved into single topology by programming using analog switches. When the circuit programs as a universal filter, it can realize low-pass, high-pass, band-pass, band-stop and all-pass filters with orthogonal and electronic controls of the natural frequency and the quality factor. When the circuit programs as a quadrature oscillator, it provides three-phase quadrature output signals which the condition of oscillation and the frequency of oscillation can be controlled orthogonally and electronically. The proposed structure can be realized based on single output OTAs which is easily implemented both commercially available integrated circuits as OTAs and complementary metal-oxide semiconductor and bipolar junction transistor OTA as IC forms. The performance of the proposed circuit is investigated by SPICE simulation using standard 0.18 μm CMOS process and experiment test using LM13600 discrete component integrated circuit as OTAs is used to confirm the workability of the new circuit.

300 mA LDO Using 0.94 μA IQ With an Additional Feedback Path for Buffer Turn-off Under Light-Load Conditions

This paper proposes a 300 mA low-dropout (LDO) regulator using an $I_{Q}$ of only $0.94~\mu \text{A}$ , which has the advantage of minimizing power consumption in the standby mode of a battery-based system. The LDO uses a source follower buffer with dynamic biasing to maintain loop stability and load transient response performance. Under light-load conditions, the buffer enters a fully-off state because there is a sub-nA bias current. Therefore, the LDO uses a dual output operational transconductance amplifier (DO-OTA) for operation under light-load conditions. The second output of the DO-OTA for light-load operation in the LDO forms an additional feedback path instead of the fully-off buffer. The second output of the DO-OTA is designed to consume a current lower than the bias current of the buffer while operating. Furthermore, the buffer in the LDO is designed for operation above 5 mA $I_{L}$ . While the buffer is operating, the dynamic biasing current of the buffer is used as the second output of the DO-OTA. The second output of the DO-OTA has lower output impedance characteristics than its main output, so the LDO can secure loop stability under light-load conditions by lowering the DC gain. As a result, the LDO exhibits load transient response performance up to 300 mA by using a minimal $I_{Q}$ under the no-load condition. The LDO is based on a 180 nm bipolar-CMOS-DMOS (BCDMOS) process and covers an area of approximately $256 \times 143 \mu \text {m}^{2}$ . The measured $I_{Q}$ is $0.94~\mu \text{A}$ under the no-load condition with a maximum load current of 300 mA.

Mixed-Mode Universal Biquad Filter Using OTAs

This paper introduces an electronically tunable mixed-mode universal biquad filter configuration employing four single output operational transconductance amplifiers (OTAs), one dual output OTA and two grounded capacitors (GCs) (ideal for integrated circuit implementation and absorbing shunt parasitic capacitances). The presented structure can realize all second-order filter functions, namely, low pass (LP), high pass (HP), band pass (BP), band reject (BR) and all pass (AP) responses in voltage mode (VM), current mode (CM), transresistance mode (TRM) and transconductance mode (TCM) using appropriate selection(s) of input signals. The cut-off frequency ([Formula: see text] and bandwidth (BW) of the realized filters can be tuned orthogonally through the transconductance (by varying the bias currents) of the OTAs. The proposed biquad configuration enjoys low active and passive sensitivities. The workability of this multifunctional biquad filter topology has been confirmed through simulations using MATLAB and Analog Design Environment (ADE) spectre tool provided by Cadence Virtuoso, using 0.18[Formula: see text][Formula: see text]m CMOS process parameter. The post-layout simulations have also been carried out to validate the theory.

Independently tunable voltage-mode OTA-C biquadratic filter with five inputs and three outputs and its fully-uncoupled quadrature sinusoidal oscillator application

This paper presents an independently tunable five-input and three-output voltage-mode biquadratic filter using five single-ended output operational transconductance amplifiers (OTAs) and two grounded capacitors. The proposed circuit can be connected to the input terminals in different ways to form a lowpass, bandpass, highpass, bandreject and allpass filter. Unlike the previously reported works, the proposed circuit can realize both non-inverting/inverting lowpass, bandpass, and bandreject filtering responses. The proposed circuit not only allows for the orthogonal controllability of the resonance angular frequency (ωo) and quality factor (Q), but also achieves independent controllability of the parameters ωo and ωo/Q without the need for control factor matching conditions. The new circuit has the following advantages: single-input three-output biquadratic filter or five-input single-output biquadratic filter with single topology, electronic tunable of parameters ωo, Q, and ωo/Q, high input impedance, resistorless structure, and no need for inverted input signals. Moreover, as an application, a quadrature sinusoidal oscillator with fully-uncoupled electronically controllable both frequency of oscillation and condition of oscillation is designed using the proposed filter. The workability of the proposed circuits is validated by OrCAD PSpice simulation program and experimental results. The given results are consistent with theoretical expectations.

Versatile Tunable Voltage-Mode Biquadratic Filter and Its Application in Quadrature Oscillator.

This paper presents a versatile tunable voltage-mode biquadratic filter with five inputs and three outputs. The proposed filter enjoys five single-ended output operational transconductance amplifiers (OTAs) and two grounded capacitors. The filter can be easily transformed into a quadrature oscillator. The filter with grounded capacitors is resistorless and electronically tunable. Either a voltage-mode five-input single-output biquadratic filter or a voltage-mode single-input three-output biquadratic filter can be operated by appropriate selecting input and output terminals. In the operation of five-input single-output biquadratic filter, the non-inverting lowpass, non-inverting bandpass, inverting bandpass, inverting highpass, non-inverting bandreject, inverting bandreject, and non-inverting allpass filtering responses can be realized by appropriately applying the input voltage signals. In the operation of single-input three-output biquadratic filter, the non-inverting/inverting lowpass, bandpass and bandreject filtering responses can be realized simultaneously. The circuit provides independent adjustment of the resonance angular frequency and quality factor, high-input impedance, and no inverting-type input voltage signals are imposed. The application in quadrature oscillator exhibits independent electronic tuning characteristic of the oscillation condition and the oscillation frequency. The theoretical analysis has been verified through OrCAD PSpice and furthermore by experimental measurements.

Fully differential fifth-order dual-notch powerline interference filter oriented to EEG detection system with low pass feature

This paper presents a fifth-order dual-notch low pass filter oriented to portable Electroencephalogram (EEG) detection system. The proposed filter is based on active realization of LC ladder topology using digitally programmable balanced output operational transconductance amplifiers (DPOTAs). This filter is utilized to reject the effect of the powerline interference at 50Hz. Furthermore, it diminishes the frequencies beyond 150Hz, which removes the third harmonic generated due to the fundamental frequency of the powerline interference. Since our objective to have small cutoff frequency less than 50Hz, the designed filter must have very low transconductance value (Gm in the order of a few nA/V). This will lead to minimizing the overall area and relaxing the associated capacitance values. Based on this, PSpice simulation results using 0.25-µm CMOS technology operating under ±0.8V voltage supply are also given. The fully differential fifth-order dual-notch LPF provides post layout simulation results (for Gm=4nA/V) as follows: THD of 0.0002% for 10μVp-p at 30Hz sinusoidal input, input referred noise spectral density of 13μV/√Hz at the passband frequencies, total standby power consumption of 51.8μW, and the notch depths of 59dB attenuation around 50Hz and 40dB attenuation around 150Hz. The overall performance makes this filter deserved to be used in aggressive EEG detection systems.

A CMOS EEG detection system with a configurable analog front-end architecture

This paper proposes a configurable analog front-end (AFE) chain architecture used in the EEG detection system. The proposed chain consists of three stages: the first and the third stages are instrumentation amplifier and programmable gain amplifier, respectively, and the second stage is notch filter with low pass feature. The proposed architecture relaxes the design of the notch filter and the analog-to-digital converter (ADC) used in building the EEG detection system. A basic building block is the digitally programmable balanced output operational transconductance amplifier (DPOTA), which is proposed to realize the AFE blocks. A successive-approximation ADC (SA-ADC) architecture is mostly designed on digital circuits in order to lower the power dissipation. Based on this, PSpice post layout simulation results for the overall EEG detection system using 0.25-µm CMOS technology are also given. The overall configurable gain/filtering chain architecture has a total gain ranging from 61 to 84 dB, a total power dissipation of 32 µW and input referred noise spectral density of 4 µV/ $$\sqrt {\text{Hz}}$$Hz.

A NOVEL CURRENT-TUNABLE MONOSTABLE MULTIVIBRATOR USING SINGLE DISO-OTA

This paper proposes a novel monostable multivibrator featuring compact topology and current-tunable property. The proposed circuit was composed of a single differential input single output operational transconductance amplifier (DISO-OTA) with a few passive components. It was operated by a negative-edge triggering signal to generate an output pulse. The pulse height and width were tunable by the bias current of DISO-OTA and the external resistors. The proposed scheme is more compact than the existing topologies. This paper presents the circuit operations and a discussion of the non-ideal issues and design considerations. To demonstrate the feasibility of the proposed circuit, a prototype circuit built with commercially available DISO-OTA IC was used to execute the experimental tests. Is-Spice simulation and experimental results were consistent with theoretical analysis.

A balanced output CMOS OTA with wide linear current tunable range

A new CMOS-based balanced output operational transconductance amplifier (BOTA) with very wide linear current tunable range is proposed in this paper. The design technique is achieved by the combination of a fully differential transconductor and an electronically variable current gain stage. The transconductance gain of the proposed BOTA can be linearly tuned by an external bias current for more than 4 decades, with less than 4% nonlinearity for the linear input-voltage range of about 0.2 V peak. The OTA is designed in 0.5 μm AMIS technology. The performance of the proposed circuit is discussed and confirmed through application example and PSPICE simulation results.

Third Order Current Mode Universal Filter Using Only Op.amp. and OTAs

A novel current mode active-only universal filter using four dual current output Operational Transconductance Amplifiers (OTAs) and three Operational Amplifiers (OAs) is presented. The circuit can realize low pass and high pass filter characteristics by choosing the suitable current output branches. The filter performance factors natural frequency (ω0), bandwidth , quality factor Q and transconductance gain gm are electronically tunable. The proposed circuit has very low sensitivities with respect to circuit active elements. From sensitivity analysis, it has been clearly shown that the proposed circuit has very low sensitivities with respect to the circuit active elements. The gain roll-off of high pass and low pass configuration is 18 dB/oc- tave. The proposed circuit facilitates integrability, programmability and ease of implementation.

TUNABLE WAVEFORM GENERATORS USING SINGLE DUAL-CURRENT OUTPUT OTAs

Two novel electronic-tunable waveform generators using a single dual-current output operational transconductance amplifier (DO-OTA) with a few passive components are proposed in this paper. The first one can produce symmetrical square and triangular waveforms simultaneously. Based on the first topology, an additional N-MOS is adopted as a switching element to construct the second proposed circuit, which can generate a pulse waveform by a negative triggering signal. The repetitive frequency and pulse width of the presented circuits are adjustable by external passive components. Moreover, the output levels of the proposed circuits can be controlled by the DO-OTA's bias currents. These waveform generators feature more compact configurations compared to the existing designs. Experimental results are close to the theoretical analyses.

Realization of current-mode high-order filters employing multiple output OTAs

Current-mode linear transformation (CMLT) high-order filters with minimum number of multiple output operational transconductance amplifiers (MOOTAs) are presented. Based on proposed design methods, we can synthesize current-mode high-order all-pole filters with minimum number of MOOTAs and all grounded capacitors efficiently. Moreover, high-frequency canonical CMLT elliptic filters with minimum number of MOOTAs and floating capacitors are also presented. Our proposed filters have the following merits: simplified design procedures, minimum number of active elements and simple design equations. Two design examples are demonstrated in this paper. Experimental results that confirm the theoretical analysis are provided.

Novel current-mode biquad filter using OTAs and DO-CCII

This paper presents a realization of a current-mode biquad filter using operational transconductance amplifiers (OTAs) and a dual current output second generation current conveyor (DO-CCII). The proposed filter is constructed with two multiple current output OTAs (MO-OTAs), one OTA, one DO-CCII and two grounded capacitors. The circuit can realize low-pass, band-pass, high-pass, band-stop and all-pass transfer functions by choosing appropriate current outputs without any matching conditions of the circuit elements. And the characteristic parameters ω0 and Q can be tuned orthogonally through adjusting the bias currents of the OTAs. The biquad filter enjoys very low sensitivities with respect to the circuit elements. An example is given together with simulated results by PSPICE. The filter circuit configuration is well suited for implementation in both bipolar and CMOS technologies.

High frequency and high precision CMOS full-wave rectifier

This paper describes a high frequency and high precision full-wave rectifier using a fully differential input and output operational transconductance amplifier (FDIO-OTA), which is very suitable for CMOS technology implementation. The system comprises a voltage to current converter, precision full-wave rectifier and a current-to-voltage converter. An input voltage signal is converted into two symmetrical current signals by using a FDIO-OTA. Two current signals will be rectified by using MOS diodes and convert into output voltage by using grounded MOS resistor. The circuit exhibits a very precise rectifier and very high operating frequency. The simulation results demonstrate the performance of the proposed circuit.

New Realizations of Current-Mode and Voltage-Mode Multifunction Filters without External Passive Elements

Abstract In this paper new voltage-mode and current-mode multifunction filters using internally compensated operational amplifiers (OP-AMPs) and single output operational transconductance amplifiers (OTAs) are presented. The proposed voltage mode multifunction filter can realize lowpass, bandpass, highpass responses simultaneously and the current-mode multifunction filter can realize lowpass, bandpass, highpass and bandstop responses simultaneously all at high output impedances. No external passive elements are required thus the circuit is suitable for monolithic implementation either with CMOS or bipolar technologies. All of active sensitivities are low. The performances of the circuits are tested using SPICE simulation program.

Simulation of Active-only Floating Inductance

A simple circuit for realizing active-only lossless floating inductor is presented. The circuit uses only two active elements ; a dual output operational transconductance amplifier and an internally compensated operational amplifier. The circuit is suitable for monolithic implementation in either bipolar or MOS technologies. Simulation results of a high-order lowpass filter using two simulated lossless floating inductors are included.

Universal active current filter using two multiple current output OTAs and one CCIII

A new universal active current filter with a single input and three outputs; which uses only two multiple current output operational transconductance amplifiers (OTAs), one third-generation current conveyor (CCIII), and two grounded capacitors is presented. In addition to the OTAs and CCIII, only capacitors are required as passive devices. The grounded capacitors make the network ideal for integration.

A general class of current-mode high-order OTA-C filters

A current-mode high-order filter configuration is introduced using multiple current output operational transconductance amplifiers OTAs. The circuit has been constructed by employing a current-mode integrator and a proportional block as basic building units. It is shown that the proposed circuit can realize a general class of high-order transfer functions. As an example, a fourth-order filter is given, together with simulated results by PSpice.

Design of current-mode multiple output OTA and capacitor filters

This paper describes a new second-order current-mode filter using dual output operational transconductance amplifiers (DO-OTA) and grounded capacitors. The circuit consists of four DO-OTAs and two grounded capacitors, is of the two integrator loop structures, and realizes the basic LP, BP, HP functions. Generation of universal current-mode filter configurations based on basic current-mode DO-OTA-C filters by using input current distributors and/or output current summers are also discussed.

Versatile current-mode biquad filter using multiple current output OTAs

A current-mode biquadratic filter is introduced using multiple current output Operational Transconductance Amplifiers (OTAs). The circuit configuration has been constructed employing current-mode integrators and a proportional block as basic building units. It is shown that the proposed circuit can realize five different biquadratic transfer functions simultaneously without changing the circuit topology. The effects of OTA non-idealities on the filter characteristics are also discussed. An example is given together with results simulated with PSpice.