Measurement of external Q factor of microwave oscillators using frequency pulling or frequency locking

Conditions are identified for the measurement of the external Q factor of microwave oscillators by use of frequency pulling or locking techniques. A small modification to a technique proposed previously for frequency locking is derived, and is extended to the case of frequency pulling. It is shown that measurements of the full locking or pulling bandwidths give information on the first derivatives, with respect to r.f.-voltage amplitude, of the device susceptance and conductance.     

Optical tuning of monolithic In/sub 0.53/Ga/sub 0.47/As/In/sub 0.52/Al/sub 0.48/As/InP modulation-doped field-effect transistor oscillators at X and R band

The authors have experimentally studied the optical control and optical tuning characteristics of monolithically integrated In/sub 0.53/Ga/sub 0.47/As/In/sub 0.52/Al/sub 0.48/As modulation-doped field-effect transistor (MODFET) oscillators operating in the X and R bands. For a 20 mu W intrinsic photoexcitation on the device, the maximum frequency shift for the X- and R-band oscillators was 8.7 and 11.7 MHz, respectively.<>     

Low Voltage CMOS LC VCO with Switched Self‐Biasing

This paper presents a switched self‐biasing and a tail current‐shaping technique to suppress the 1/f noise from a tail current source in differential cross‐coupled inductance‐capacitance (LC) voltage‐controlled oscillators (VCOs). The proposed LC VCO has an amplitude control characteristic due to the creation of negative feedback for the oscillation waveform amplitude. It is fabricated using a 0.13 µm CMOS process. The measured phase noise is ‐117 dBc/Hz at a 1 MHz offset from a 4.85 GHz carrier frequency, while it draws 6.5 mA from a 0.6 V supply voltage. For frequency tuning, process variation, and temperature change, the amplitude change rate of the oscillation waveform in the proposed VCO is 2.1 to 3.2 times smaller than that of an existing VCO with a fixed bias. The measured amplitude change rate of the oscillation waveform for frequency tuning from 4.55 GHz to 5.04 GHz is 131 pV/Hz.     

Sliding-Mode Amplitude Control Techniques for Harmonic Oscillators

This paper investigates both theoretical and implementation-level aspects of switching-feedback control strategies for the development of harmonic oscillators. We use sliding-mode compensation based on various norms of the system state to achieve amplitude control over a wide-tuning range. A 7.6-MHz I/Q LC oscillator is developed and tested. Measurements show that implementation of the proposed switch-based amplitude controller provides accurate amplitude control over the entire frequency tuning range while inducing only a minor phase noise degradation (of less than 2 dBc/Hz).     

Silicon-based distributed voltage-controlled oscillators

Distributed voltage-controlled oscillators (DVCOs) are presented as a new approach to the design of silicon VCOs at microwave frequencies. In this paper, the operation of distributed oscillators is analyzed and the general oscillation condition is derived, resulting in analytical expressions for the frequency and amplitude. Two tuning techniques for DVCOs are demonstrated, namely, the inherent-varactor tuning and delay-balanced current-steering tuning. A complete analysis of the tuning techniques is presented. CMOS and bipolar DVCOs have been designed and fabricated in a 0.35-μm BiCMOS process. A 10-GHz CMOS DVCO achieves a tuning range of 12% (9.3-10.5 GHz) and a phase noise of -103 dBc/Hz at 600 kHz offset from the carrier. The oscillator provides an output power of -4.5 dBm without any buffering, drawing 14 mA of dc current from a 2.5-V power supply. A 12-GHz bipolar DVCO consuming 6 mA from a 2.5-V power supply is also demonstrated. It has a tuning range of 26% with a phase noise of -99 dBc/Hz at 600 kHz offset from the carrier     

Fully-integrated wideband CMOS VCO with improved f–V linearity and low tuning sensitivity

A technique to improve the linearity of the frequency-voltage (f - V) characteristic and to reduce the differential tuning sensitivity, KVCO, of voltage-controlled oscillators (VCOs) is proposed. The VCO designed using the linearisation technique is tunable from 806 to 1113 MHz with a 34 tuning range and exhibits a nearly constant KVCO of 62 MHz/V over the entire frequency range.     

Initial observations of optical injection locking of oscillators using heterojunction bipolar transistors

For the first time, optical phase control of a hybrid heterojunction bipolar transistor (HBT) oscillator has been achieved. The results strongly indicate that the HBT is a suitable device for optically controlled oscillators. At a frequency of oscillation of 500 MHz a locking range of more than 15 MHz was measured ( Delta f/f equivalent to 3%). The optical tuning range of the oscillator exceed 25 MHz.<>     

A Stable Loss Control Feedback Loop for VCO Amplitude Tuning

In practical implementations of LC oscillators in which the quality factor of the tank is dominated by the quality factor of the inductor, due to dependence of the oscillation amplitude on the square of the oscillation frequency and the bias current of the LC tank, a stable amplitude control loop is essential to maintain a constant oscillation amplitude over the tuning range of the voltage-controlled oscillator (VCO) and to optimally bias the VCO over different conditions. In this paper, an enhanced loss control scheme incorporating an integral feedback to automatically tune the oscillation amplitude of LC oscillators is proposed. The proposed loss control feedback (LCF) loop is conditionally stable with an easy stability requirement to meet and its stability is examined: 1) by linearizing the system around the stable point using a perturbation method; and 2) by numerically solving the nonlinear differential equation of the LCF loop describing the transient behavior of the step response of the loop. A prototype including the LC VCO and the proposed LCF loop has been implemented in TSMC 0.35-mum CMOS process and occupies an area of 0.057 mm² and consumes 8.1 mA from a 2.8-V power supply. The LCF loop, with respect to the VCO, has an overhead of 25% on the area and consumes only 1.3% of the total power. Measurement results of the proposed LCF loop show an 11 dBm amplitude tuning range from -16 dBm to -5 dBm at any frequency over the 2-2.5-GHz tuning range of the VCO. The step response of the loop has a settling time less than 0.5 ns     

Stability and distortion in tuneable low frequency sinusoidal oscillators

The theoretical principles involved in the design of tuneable oscillators are presented in the context of a practical design which generates a sinusoidal output with a constant amplitude and low harmonic content over the range 7-2500 Hz in three overlapping bands, each with a continuous tuning range exceeding 20 : 1. We introduce a figure of merit ζ, the product of the fractional amplitude variation on tuning and the fractional harmonic content, and show that ζ = LλδL/L where L is the insertion loss at the resonant frequency w, (essentially L = Q^-1) of the frequency selective element, δL/L its fractional variation on tuning and λ is a constant depending on the structure of the oscillator and of the amplitude control system. When a subsidiary low-pass control loop characterized by a time constant T, which influences the settling time, is used, λ is inversely proportional to w _o T.     

Piezoelectric-transducer-controlled tunable microwave circuits

This paper introduces a new method to tune microwave circuits of phase shifters, filters, resonators, and oscillators, controlled by a piezoelectric transducer (PET) with computational and experimental results. An optimized PET-controlled phase shifter is demonstrated to operate up to 40 GHz with a maximum total loss of 4 dB and phase shift of 480°. PET-controlled tunable bandpass filter, ring resonator, and one-dimensional photonic-bandgap resonator show a very wide tuning bandwidth of 17.5%-28.5% near 10 GHz with little performance degradation. A new PET-controlled or voltage-controlled dielectric-resonator oscillator (DRO) is demonstrated with a tuning bandwidth of 3.7% at the center frequency of 11.78 GHz. The tuning bandwidth is slightly less than that of a mechanical tuning using a micrometer-head-controlled tunable DRO with a tuning bandwidth of 4.7%. The new tuning method should have many applications in monolithic and hybrid microwave integrated circuits     

Wide-Band Varactor-tuned Coaxial Oscillators

An experimental investigation into the effects of package and circuit reactances on wide-band varactor-tuned oscillators is described. The results are used to design an X-band Gunn coaxial oscillator with a tuning range in excess of 3 GHz. It is shown that the stray reactance, junction capacitance, and bond-wire inductance affect the varactor tuning characteristics. The characteristics are conveniently displayed by the reflection phase variation with tuning voltage and frequency. A general theory for wide-band varactor-tuned oscillators is presented which is related to the impedance characteristics. These results are used to design three coaxial varactor-tuned oscillators. The first two oscillators are series arrangements while the third oscillator is a parallel arrangement. A simple circuit technique is used to improve the tuning range of each arrangement. This technique is shown to increase the coupling to the varactor diode and decrease the oscillator Q by reactance compensation.     

The optical control of IMPATT oscillators

This paper describes methods of controlling the frequency of IMPATT oscillators using optical rather than electrical signals. Analytic theories of optical tuning and injection locking are presented. Results from a comprehensive large signal computer model of the optically controlled IMPATT oscillator are given, illustrating the importance of the composition of the optically generated current on the optical control performance and demonstrating the capability of optical control for rapid frequency tuning. Finally, recent experimental work on optical tuning effects in W-Band IMPATT oscillators is presented.     

Modeling of a Neural Pattern Generator with Coupled nonlinear Oscillators

A set of van der Pol oscillators is arranged in a network in which each oscillator is coupled to each other oscillator. Through the selection of coupling coefficients, the network is made to appear as a ring and as a chain of coupled oscillators. Each oscillator is provided with amplitude, frequency, and offset parameters which have analytically indeterminable effects on the output waves. These systems are simulated on the digital computer in order to study the amplitude, frequency, offset, and phase relationships of the waves versus parameter changes. Based on the simulations, systems of coupled oscillators are configured so that they exhibit stable patterns of signals which can be used to model the central pattern generator (CPG) of living organisms. Using a simple biped as an example locomotory system, the CPG model generates control signals for simulated walking and jumping maneuvers. It is shown that with parameter adjustments, as guided by the simulations, the model can be made to generate kinematic trajectories which closely resemble those for the human walking gait. Further-more, minor tuning of these parameters along with some algebraic sign changes of coupling coefficients can effect a transition in the trajectories to those of a two-legged hopping gait. The generalized CPG model is shown to be versatile enough that it can also generate various n-legged gaits and spinal undulatory motions, as in the swimming motions of a fish.     

Varactor diode for tuning high-power solid-state microwave oscillators

A novel varactor diode has been developed for tuning high-power microwave solid-state oscillators. The resulting output power against frequency remains much flatter than conventional high-power varactor-tuned oscillators.     

Optical synchronization of millimeter-wave oscillators fordistributed architecture

A review of various methods of phase and frequency synchronization of active MMIC based transmit/receive modules is presented, and particular emphasis is placed on the synchronization of oscillators through the use of an indirect subharmonic optical injection locking technique. In this approach, the nonlinear behavior of large-signal modulated laser diodes and solid-state oscillators is exploited to extend the bandwidth of the synchronizing link to the millimeter-wave frequency range. Experimental results of the phase and frequency coherency of two 21.5 GHz FET oscillators are reported. Optimum performance is achieved at a subharmonic factor of 1/4, with a locking range of 84 MHz and a phase noise degradation of only 14 dB. The phase coherency measurement of two injection-locked oscillators points to a phase shift, which is introduced as a result of the frequency detuning between the slave and master oscillator signals. A scheme to correct for this phase error is presented     

Field-induced coupled quantum-well oscillators

A study of field-induced coupled quantum-well oscillators due to the interwell coherent oscillation is presented. The evolution of an electron wave packet in an asymmetric coupled quantum-well structure is described by the application of the time-development operator of the time-dependent Schrodinger equation. By adjusting the applied field, various resonant conditions giving rise to different oscillation frequencies can be obtained in a single device. Direct frequency tuning, amplitude variation, and dipole matrix element due to the external field are also investigated     

Oscillation Characteristics of Millimeter-Wave IMPATT Diodes Mounted in Low-Impedance Waveguide Mounts (Short Papers)

Experiments on dc-bias-current-tuned IMPATT diodes mounted in low-impedance waveguide mounts are described. Broad-band bias-current-tuned IMPATT oscillators were obtained which cover almost the full waveguide band; 20-, 24-, and 18-GHz tuning bandwidths were obtained with the R-500, R-620, and R-740 waveguide, respectively. From experiments it became evident that there are some suitable relations for broad-band bias tuning among the diode breakdown voltage, the oscillation frequency, and the waveguide dimension. The results are very useful for the design of the circuit and diode parameter for broad-band millimeterwave IMPATT sweep oscillators. The feasibility of applying bias-current-tuned IMPATT oscillators to a broad-band measuring instrument is expected.     

Investigations on optically controlled millimeter wave Gunn oscillators

There is a growing interest in optically controlled millimeter wave oscillators. In this paper, we have investigated the external-circuit impedances of an optically controlled millimeter wave subharmonic Gunn diode oscillator, which is illuminated by GaAs/GaAlAs laser beam. The variation of the external-circuit impedances looking outward from the Gunn diode with respect to the optical injection plasma density are calculated based on a field analysis method. The results give some useful conclusions for optically controlled millimeter wave Gunn diode oscillator design. Experimentally an optical tuning frequency shift of 7MHz is achieved at W-band.     

A varactor configuration minimizing the amplitude-to-phase noise conversion in VCOs

Amplitude-to-phase-noise conversion due to varactors can severely limit the close-in phase noise performance in LC-tuned oscillators. This work proposes a rigorous analysis of this phenomenon, which highlights the fundamental limitations of single-ended tuned and differentially tuned diode varactor configurations. The back-to-back varactor topology is identified as a suitable solution to linearize the tank capacitance. The amplitude to phase noise conversion is greatly attenuated and the 1/f/sup 3/ phase noise is drastically reduced, without impairing the achievable tuning range. These results are validated through circuit simulations in an existing 0.35-/spl mu/m CMOS technology.