New Rc-Active oscillator configuration employing unity-gain amplifiers

A new sinusoidal oscillator configuration is proposed which employs op-amps as unity-gain amplifiers. The proposed circuit offers independent single-element controls for adjusting the condition of oscillation and oscillation frequency and has very good frequency stability. Practically, the circuit works well over a frequency range much higher than possible with other known types of oscillators (which use op-amps as ±K-gain or infinite-gain VCVSs). The proposed configuration also provides useful prototypes to derive novel switched-capacitor oscillators.     

Composite-amplifier Wien-bridge oscillator with improved limit-cycle stability

The problem of undesirable low-frequency oscillation which may occur in oscillators with composite amplifiers is discussed. The article shows how the Wien-bridge oscillator proposed by Carlosena et al (1990) should be modified in order to avoid such oscillation and ensure stable operation of the oscillator and good properties of the sinusoidal waveform generated.<>     

Current amplitude control circuits suitable for current-modeoscillators

A novel current amplitude control circuit suitable for current-mode oscillators is proposed. The circuit is a modified version of the well-known Gilbert gain cell. The technique obtains independent control of oscillation amplitude and small-signal current gain. As an example, the amplitude control circuit is applied to a current-mode oscillator. Simulations were carried out using HSPICE with 0.8 μm Nortel BiCMOS technology and Motorola RF transistors. Simulated results demonstrate that the nonlinear current gain control circuit behaves in a well defined manner. Low distortion and high frequency oscillations are easily obtained when the circuit is applied to a current-mode oscillator     

Nonlinear contribution to oscillation-frequency sensitivity in RC integrated oscillators

The sensitivity of oscillation frequency of integrated oscillators to varying parameters or elements is usually so high for simple designs that the advantages of integrated circuits are completely offset. Satisfactory performance can be achieved for some applications by the use of low-temperature-coefficient thin-film components; by the use of the temperature tracking of elements in monolithic circuits; and by the use of active compensation circuits. These methods are in general based on a linear model of the oscillator and often require amplifiers with very insensitive gain characteristics or the inclusion of automatic gain control (AGC) circuits. This paper describes a compensation technique can be used in conjunction with linear techniques to reduce second- order contributions to sensitivity of frequency to bias and to gain. An experimental oscillator is described that uses this compensation technique. It has a zero of oscillation-frequency sensitivity to manually set gain changes and an order-of-magnitude decrease in frequency deviation over the described gain range. All the required compensating nonlinear functions are realized by diode-resistor networks.     

CMOS realization of single-resistance-controlled and variable frequency dual-mode sinusoidal oscillators employing a single DVCCTA with all-grounded passive components

In this paper, two new designs are proposed for sinusoidal oscillators based on a single differential voltage current conveyor transconductance amplifier (DVCCTA). Each of the proposed circuits comprises a DVCCTA combined with passive components that simultaneously provides both voltage and current outputs. The first circuit is a DVCCTA-based single-resistance-controlled oscillator (SRCO) that provides independent control of the oscillation condition and oscillation frequency by using distinct circuit parameters. The second circuit is a DVCCTA-based variable frequency oscillator (VFO) that can provide independent control of the oscillation frequency by adjusting the bias current of the DVCCTA. In this paper, the DVCCTA and relevant formulations of the proposed oscillator circuits are first introduced, followed by the non-ideal effects, sensitivity analyses, frequency stability discussions, and design considerations. After using the 0.35-μm CMOS technology of the Taiwan Semiconductor Manufacturing Company (TSMC), the HSPICE simulation results confirmed the feasibility of the proposed oscillator circuits.     

An electronically tunable current-mode quadrature oscillator using PCAs

This article presents a new realisation of active RC sinusoidal oscillator with electronically tunable condition and frequency of oscillation (FO). As compared to the class of three resistors, two capacitors (3R-2C)-based canonic oscillators, the circuit proposed here uses only two resistors and two capacitors as the passive components and still provides non-interactive tuning laws for the condition of oscillation and the FO. The proposed circuit employs new bipolar programmable current amplifier as the active building block and is capable of simultaneously providing two explicit quadrature current outputs. SPICE simulation results have been included to verify the workability of the circuit as an oscillator and the tuning range of the FO.     

Comment on ‘Discussion on Barkhausen and Nyquist stability criteria’

This comment is related to the recently published article entitled “On ‘Discussion on Barkhausen and Nyquist stability criteria’, Analog Integrated circuits and signal processing, Vol. 70, pp. 443–449, 2012. In this article the authors considered one of the possible four alternatives of the Wien-bridge oscillator that was previously considered in the article entitled “Discussion on Barkhausen and Nyquist stability criteria”, Analog Integrated Circuits and Signal Processing, Vol. 62, pp. 327–332, 2010, which depicts the failure of Barkhausen criterion concerning the determination of the condition of oscillation startup of sinusoidal oscillation. In the above mentioned articles the operational amplifier used is assumed ideal. In this comment it will be shown that the Wien-bridge oscillator circuit used in the above mentioned articles can behave as a sinusoidal oscillator only at relatively high frequencies when the operational amplifier can be considered non-ideal. At relatively low frequencies; when the operational amplifier can be considered ideal, the same circuit behaves as a relaxation oscillator with a square wave output rather than a sinusoidal output.     

Current-Mode High Output Impedance Sinusoidal Oscillator Configuration Employing Single FTFN

In this study, a general current-mode high output impedance sinusoidal oscillator configuration is proposed. The proposed oscillator configuration uses a single four terminal floating nullor (FTFN), two capacitors and five resistors. The oscillator configuration exhibits high output impedance which makes easy to drive loads without using any buffering devices and provide non-interactive control of oscillation condition and oscillation frequency. The proposed topology also yields single frequency oscillators with reduced number of passive components. All of the proposed oscillators permit good frequency stability and exhibit low active and passive sensitivities. Theoretical analysis is verified with experimental results.     

Electronically tunable multiphase sinusoidal oscillator using translinear current conveyors

A new electronically tunable current-mode multiphase sinusoidal oscillator based on translinear current conveyors is presented. The proposed oscillator circuit, which employs only one translinear current conveyor and one grounded capacitor for each phase, can generate arbitrary N output current equal-amplitude signals that are equally spaced in phase (N being even or odd), all at high output impedance terminals. The frequency of oscillation and the condition of oscillation can be controlled electronically and independently through the bias current of the translinear current conveyor. The proposed structure also has simple circuitry, low-component count, and is highly suitable for integrated circuit implementation. The theoretical results were verified by PSPICE simulation. In addition, the modification of the N sinusoidal oscillators to construct a programmable multiphase oscillator is also discussed.     

A new single MCCCDTA based Wien-bridge oscillator with AGC

This paper presents a new current-mode Wien-bridge oscillator with automatic amplitude control. The oscillator only employs single MCCCDTA as the active element and provides two current outputs with small distortion from high output impedances. Its oscillation condition and frequency can be tuned electronically, linearly and independently through tuning bias currents of MCCCDTA. The circuit simulation results are in agreement with theory.     

On modified Wien-bridge oscillator and astable oscillator

The present article is related to the recently published paper given in (Abuelma’atti and Khalifa, Analog Integr Circuits Signal Process, 73:989–992, 2012), which depicts the possible relation between the modified Wien-bridge circuit used by the authors of references (Singh, Analog Integr Circuits Signal Process 48:251–255, 2006; Singh, Analog Integr Circuits Signal Process, 50:127–132, 2007; Singh, Analog Integr Circuits Signal Process, 62:327–332, 2010; Wangenheim, Analog Integr Circuits Signal Process, 66:139–141, 2011; Martinez-Garcia et al., Analog Integr Circuits Signal Process, 70:443–449, 2012), and the comparator-based relaxation oscillator. In particular, in the referenced Mixed Signal Letter (Abuelma’atti and Khalifa, Analog Integr Circuits Signal Process, 73:989–992, 2012), the authors assert that the modified Wien-bridge oscillator circuit under discussion, used previously in the aforementioned referenced articles, can behave as a sinusoidal oscillator only at relatively high frequencies when the operational amplifier can be considered non-ideal. In addition, at relatively low frequencies, when the operational amplifier can be considered ideal, the same circuit would behave as a relaxation oscillator with a square wave output rather than a sinusoidal output. However, this paper reveals that this assertion is not strictly correct, because in both cases (in low and high frequencies), the generated waveform at the circuit output is a sinusoidal signal, with the possibility of be cut out, depending on proper circuit dimensioning (according to the oscillation criterion) as well as the oscillation frequency and the properties of the amplifier (slew rate, and frequency response).     

Fractional-order Wien-bridge oscillator

The classical Wien-bridge sinusoidal oscillator is studied, when both of the capacitors of the oscillator acquire a fractional order. Accordingly, the Wien oscillator is described by a set of fractional-order nonlinear differential equations. It is shown that sinusoidal oscillations are preserved but the phase-shift between the waveforms of the two state variables and the frequency of oscillation both depend on the fractional-order, leading to a significant advantage over the integer-type Wien oscillator. Findings are validated via numerical simulations     

Wien-type oscillators using CCII+

The purpose of this paper is to show that exists a close relationship between some CCII⁺ based sinusoidal oscillators and the RC active second order oscillators with a single VCVS. These structures with CCII⁺ may be derived from the classic Wien-bridge oscillator, and four of them exhibit practical interest. They are canonical, the oscillation condition can be adjusted by a single resistor, and furthermore, they may be designed with the same procedure as their voltage amplifier counterparts. Experimental and simulation results supporting the theoretical analysis are given.     

Linearly tunable quadrature oscillator derived from LC Colpitts structure using voltage differencing transconductance amplifier and adjustable current amplifier

The paper deals with an interesting oscillator solution derived from LC Colpitts circuit structure. Electronically controllable current gain of the current amplifier is utilized for driving of oscillation condition together with two transconductances in frame of voltage differencing transconductance amplifier for adjusting of frequency of oscillation. In the proposed structure these elements replace common bipolar transistor and metal coil. Designed circuit offers important advantages, i.e. absence of metal coil, quadrature outputs, amplitudes of generated signals independent of tuning process, linear electronic control of oscillation frequency (independent of oscillation condition). Implementation of circuit for amplitude stabilization and automatic control of oscillation condition for designed circuit is simple. These benefits are not available in classical LC Colpitts structures or in many well-known third-order oscillators. The theoretical conclusions are supported by experiments with behavioral representation employing commercially available devices and also by simulations using CMOS model.     

A high-frequency electronically tunable quadrature oscillator

An architecture composed of mutually regenerative oscillators is introduced. It has been used to design a low-noise high-frequency voltage-controlled oscillator (VCO) capable of producing two output signals in quadrature with essentially identical properties. The phase relation between the quadrature outputs is frequency dependent and extremely stable. A novel way of coupling the regenerative oscillators is suggested in order to improve the frequency stability of the coupled oscillator system. Results obtained from a test chip have verified the viability of the oscillator concept. The oscillator circuit has been realized in a medium-frequency bipolar process. The tuning range extends to 500 MHz. At an oscillation frequency of 200 MHz, measured phase noise was -121 dBc/Hz at 1-MHz distance from the carrier.<>     

7-decade tuning range CMOS OTA-C sinusoidal VCO

A new operational transconductance amplifier-capacitor (OTA-C) based sinusoidal voltage-controlled oscillator (VCO) has been designed and fabricated. The oscillation frequency of which can be tuned from 74 mHz to 1 MHz. The VCO uses a new OTA whose transconductance is adjusted by using a set of special current mirrors. These current mirrors operate in weak inversion and their gain can be controlled continuously through a gate voltage over many decades. This is the first report of such a wide tuning range for CMOS sinusoidal oscillators. Experimental results are provided     

A general method to predict the amplitude of oscillation in nearly sinusoidal oscillators

In this paper, a general methodology for predicting the amplitude of oscillation in nearly sinusoidal oscillators is presented. The method relies on the recently proposed projection technique for the computation of the center manifold and on the Hopf normal form theory to approximate the corresponding limit cycle in state space. The Colpitts oscillator is selected as a case study and, for this circuit, a closed-form expression for the amplitude of oscillation is derived as a function of the circuit parameters.     

A Giga-Hertz-Range MOS Current-Tunable Sinusoidal Oscillator with Inherent Automatic Amplitude Control

A new all MOS current-mode current-tunable sinusoidal oscillator is proposed. Using a standard 0.8 CMOS fabrication process, an oscillation frequency of greater than 1 GHz can be achieved, with only 3.3 V supply voltage, and with less than 5–mW power consumption. Most importantly, a symmetrical automatic amplitude control or AGC function is also inherent in the circuit.     

Current-conveyor-based single-element-controlled and current-controlled sinusoidal oscillators

A new single-element-controlled sinusoidal oscillator circuit that incorporates two second generation current conveyors (CCIIs), two grounded capacitors and two resistors is presented and analysed. The circuit is beneficial to monolithic integrated circuit implementation by the use of grounded capacitors. In addition, a new current-controlled sinusoidal oscillator using only two second generation current controlled conveyors (CCCIIs) and two grounded capacitors can be achieved by replacing CCIIs and resistors series at X terminals with CCCIIs. The oscillators provide extremely low passive ω₀-sensitivities and good frequency stability. Moreover, the oscillation frequencies of the CCII-based and the CCCII-based oscillators can be controlled, respectively, by a grounded resistor and by an external bias current. Experimental and SPICE simulation results that confirm the theoretical predictions are given.     

A Novel Single-Resistance-Controlled Sinusoidal Oscillator Employing Single Operational Transresistance Amplifier

A novel operational transresistance amplifier (OTRA)-based single-resistance-controlled sinusoidal oscillator (SRCO) is proposed. It uses single OTRA, three resistors and two capacitors. To the best knowledge of author, this is the first oscillator constructed with single OTRA. The oscillator circuit provides independent control of oscillation frequency without disturbing oscillation condition by a resistor. It has also low passive sensitivities. The oscillator circuit is insensitive to parasitic input capacitances and input resistances due to zero internally grounded input terminals of OTRA. PSPICE simulations are given to verify the theoretical analysis.