Electronic frequency tuning of TRAPATT oscillators

Experimental results of a novel electronically tunable microstrip Trapatt oscillator employing varactor diodes arc presented. A tuning range of 20 MHz, limited by the low voltage breakdown of the varactor diodes and the number of tuning stages used, for an oscillator with a centre frequency of 1.6 GHz and an output power of 9 W, was observed and found to be in good agreement with theory.     

Electronic tuning of stable transferred electron oscillators

The problem of electronic tuning of microwave osciilator structures characterized by high energy storage and hence low noise is considered. The evolution of a wide-band varactor tuned J-band oscillator is described, and analytical criteria are presented which determine the position of the varactor diode and the theoretical maximum tuning range available including Varactor loss. Experimental results confirm the validity of the circuit model used for the proposed oscillator structures.     

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.     

An electronically tuned Gunn oscillator circuit

A novel waveguide Gunn oscillator circuit is described that permits wide-band mechanical and electronic (varactor) tuning. A feature of the circuit is that a circuit model can be devised that accurately predicts the oscillator characteristics and that, therefore, can be used to formulate a realistic oscillator design procedure.     

Rotational Driven RF Variable Capacitors With Post-CMOS Processes

A ring-shaped on-chip tunable capacitor is proposed and fabricated with CMOS-compatible micromachining processes for radio frequency integrated circuits (RFICs). The rotationally driven variable capacitor features a much higher axial mechanical stiffness compared to its conventional straight-line-driven counterpart, and therefore, can effectively depress the instability caused by environmental vibration when the varactor is used in mobile systems. Meanwhile, the rotationally driven intedigitated capacitor is designed to be very flexible for wide range of electrostatic tuning. Near-room-temperature micromachining techniques are developed for post-CMOS integrating the tunable capacitors into RFIC chips. The fabricated varactor is measured with a tuning ratio of 2.1:1 under an actuation of 12 V. Q-factor is measured as 51.3 at 1 GHz and 35.2 at 2 GHz, while self-resonance frequency is as high as 9.5 GHz. The rotationally driven tunable capacitor shows about two orders of magnitude higher antivibration capability compared to the conventional straight-driven one. Therefore, the high-performance CMOS-compatible tunable capacitors are promising for practical RFIC applications in mobile electronic telecom systems.     

Analysis of a Waveguide Mounting Configuration for Electronically Tuned Transferred-Electron-Device Oscillators and its Circuit Application

Theoretical analysis of a waveguide-post mounting configuration employed for high electronic (varactor) tuning of a transferred-electron-device oscillator is presented. The resulting two-port-coupling network representation is also used to derive the impedance of the post structure as an obstacle to the dominant TE/sub 10/ mode in the waveguide. Obstacle measurements conducted on the post structure for the incident TE/sub 10/ mode are found to be in very good agreement with the theory. This network representation is then applied to a practical transferred-electron-device oscillator reported elsewhere. It has been able to successfully explain the characteristic features of the oscillator. It is observed that the main source of discrepancy between the theoretical and experimental characteristics could be attributed to a lack of knowledge of the precise values of the package parasitic elements. The nature of the theoretical varactor-tuning characteristic predicted by the model is discussed and indicated for a particular configuration.     

A 50-GHz silicon IMPATT diode oscillator and amplifier

Recent experimental observations on a silicon impact avalanche transit-time diode oscillator and amplifier CW-operated at 50 GHz are presented. 1) CW oscillation power of 100 mW was obtained at an overall efficiency of 2 percent. The oscillation frequency was continuously tunable over a 1.3-GHz range by a sliding short. 2) Phase-locking has been achieved with a maximum normalized gain-bandwidth product of 0.1. The minimum locking signal power required for a 500-MHz locking bandwidth was 20 dB below the oscillator output. 3) Electronic tuning of the oscillator frequency was demonstrated by placing a millimeter-wave varactor diode in the tuning circuit. The output frequency versus the bias voltage on the varactor diode was linear with maximum frequency deviation of 300 MHz. Frequency modulation of the oscillator by driving the varactor with a sinusoidal source was obtained at a modulation frequency of 50 MHz. 4) Stable amplification with 13-dB gain was obtained, centered at 52.885 GHz with a 3-dB bandwidth of 1 GHz. The maximum output power obtained was 16 mW. Higher gain of about 17 dB was obtained at a reduced bandwidth. The noise figure of the amplifier was 36 dB. Equivalent circuits for the oscillator and the amplifier are derived. The calculated results agree reasonably well with the experimental observations.     

A circuit technique for broadbanding the electronic tuning range of Gunn oscillators

A circuit technique is described whereby the electronic tuning range obtained by varactor tuning solid-state oscillators, such as Gunn oscillators, can be improved. The principle of the technique has been demonstrated by doubling the tuning range obtained from a coaxial X-band Gunn oscillator using distributed circuit elements. An analytical expression for the improved tuning range is presented and predictions for the improvement in an existing microstrip X-band oscillator using chip devices given.     

U-band shield suspended-stripline Gunn DRO and VCO

A millimeter-wave IC dielectric resonator oscillator (DRO) is proposed. Equations that give the resonant frequency of the dielectric resonator DR in suspended stripline (SSL) are derived. A U-band voltage-controlled oscillator (VCO) with varactor tuning also has been developed. The Gunn diode and varactor used in both of the oscillators are commercially available packaged devices. Restrictions on the performance of the oscillators imposed by packaged and mounted networks and the self-characteristics of the solid-state devices have been analyzed. An electronic tuning range greater than 1000 MHz with an output power exceeding 15 dBm across the bandwidth in the 53-GHz region has been realized for the SSL VCO. An SSL DRO with an output power of more than 17 dBm and a mechanical tuning range of 1.5 GHz in the 54-GHz region has been achieved     

Linearization of oscillation frequency for integrated LC-VCO with inversion-mode varactor

Metal-oxide semiconductor (MOS) varactors are widely used in voltage-controlled oscillators (VCOs) due to the need for a tunable capacitance. Two types of varactors that have been integrated on-chip include the inversion-mode and accumulation-mode types. The inversion-mode varactor offers immunity to latch-up, but suffers from a non-linear C(V) characteristic which directly leads to a nonlinear oscillation frequency tuning curve. This paper proposes an oscillation frequency linearization technique for LC-VCO with an inversion-mode varactor. The linearity of the frequency tuning curve is improved by linearization of C(V) characteristics of the inversion-mode varactor. A new varactor configuration consisting of varactor units and resistor divider network is proposed. The single-switch integrated LC-VCO with the proposed varactor configuration is fabricated in TSMC 0.18 μm CMOS technology. The improvement of linearity of the frequency tuning curve has been verified using mathematical models and measurement results.     

基于基片集成波导谐振器的压控振荡器设计

设计了一种基于基片集成波导谐振器的X波段压控振荡器。首先分析了串联反馈式振荡器以及基片集成波导谐振器的理论,然后在高频电磁仿真软件ADS中进行仿真和设计,并通过将变容管合理地引入谐振器,实现了电调谐的目的。最终设计完成了一个工作于X波段的基片集成波导压控振荡器。此压控振荡器与传统的介质压控振荡器(DRO)相比,具有稳定性高、平面化以及成本低的优点。由于采用了ADS中的联合仿真功能进行振荡器的设计,仿真结果的准确性得到了提高,减小了实物的调试工作量。测试结果为:工作频率为7 GHz,调谐范围为30 MHz,输出功率≥7 dBm,谐波抑制度≥22 dBc,相位噪声优于-106 dBc/Hz@100 kHz。     

Hybrid Narrow-Band Tunable Bandpass Filter Based on Varactor Loaded Electromagnetic-Bandgap Coplanar Waveguides

A varactor-loaded resonator inserted between two Bragg reflectors has been implemented to design high-selectivity tunable bandpass filters. First, a mechanical tuning method is demonstrated. A varactor tunable bandpass filter is then implemented at 9 GHz, yielding good agreement between computational and experimental results. The tuning range reaches 3.5% with a loaded quality factor$Q_L =40$, a maximum insertion loss of 4.75 dB, and a return loss exceeding 20 dB. The theory is carefully explained, showing the importance of the parameters of the Bragg reflectors and of the resonator, in particular, the effect of diode-case parasitics and varactor position with respect to the resonator. A large-signal experimental analysis is done, showing a maximum allowable input power of a few dBm. Finally, possible filter improvements are discussed, and simulations with a microelectromechanical systems varactor are shown.     

Simulation Investigation of Millimeter Wave Varactor-tuned Transmission Cavity-stabilized Oscillator

A new circuit configuration for millimeter wave varactor-tuned transmission cavity-stabilized oscillator has been proposed in this paper. Compared to conventional varactor-tuned reflection cavity-stabilized oscillator, in this configuration, a high quality factor transmission cavity directly coupled to varactor diode is employed to improve the performances of the oscillator. The operation frequency of this oscillator can be tuned by varying the resonant frequency of the transmission cavity through changing bias voltage of the varactor diode. An equivalent circuit model for the oscillator has been presented in order to theoretically investigate the performance characteristics of the oscillator. On the basis of this model, electrical tuning characteristics have been studied. Mode jumping phenomena during electrical tuning process have been analyzed for obtaining stable operations of the oscillator. The analytical formulae of quality factor and efficiency have been derived in terms of relevant circuit parameters. Particular emphasis has been paid on several circuit parameters which have a substantial impact on circuit performance. Some design considerations have been pointed out according to the simulation results, which are useful to the design and fabrication of this type of oscillators.     

A 110–140 GHz Millimeter-Wave VCO Using Varactor and Bulk Effective Technique in 65 nm CMOS Process

In this paper, an enhanced voltage controlled oscillator (VCO) at center frequency 125 GHz with tuning rang of 24% is presented. The proposed idea is based on the tuning capacitance using MOS varactor. The structure is consisted of applying an MOS varactor capacitor to the drain and bulk (in parallel) of NMOS transistor in 65 nm CMOS standard technology. The obtained output of the proposed VCO at 2nd harmonic is tunable at 110–140 GHz frequency with applying?±?1.2 input tuning voltage. Simulation results of the proposed circuit are obtained after extracting post layout (with total chip size of 0.07 mm²) and confirm theoretical results. Compared to the resent designs, the obtained results indicate that the proposed circuit has high tuning range, low die area and a good figure of merit @ 1.2 power supply voltage.

     

A Wide Tuning-Range CMOS VCO With a Differential Tunable Active Inductor

By utilizing a differential tunable active inductor for the LC-tank, a wide tuning-range CMOS voltage-controlled oscillator (VCO) is presented. In the proposed circuit topology, the coarse frequency tuning is achieved by the tunable active inductor, while the fine tuning is controlled by the varactor. Using a 0.18-$muhbox m$CMOS process, a prototype VCO is implemented for demonstration. The fabricated circuit provides an output frequency from 500 MHz to 3.0 GHz, resulting in a tuning range of 143% at radio frequencies. The measured phase noise is from$-$101 to$-$118 dBc/Hz at a 1-MHz offset within the entire frequency range. Due to the absence of the spiral inductors, the fully integrated VCO occupies an active area of$hbox 150times hbox 300 muhbox m^2$.     

Frequency dependence on bias current in 5 GHz CMOS VCOs: impact on tuning range and flicker noise upconversion

The tuning curve of an LC-tuned voltage-controlled oscillator (VCO) substantially deviates from the ideal curve 1//spl radic/(LC(V)) when a varactor with an abrupt C(V) characteristic is adopted and the full oscillator swing is applied directly across the varactor. The tuning curve becomes strongly dependent on the oscillator bias current. As a result, the practical tuning range is reduced and the upconverted flicker noise of the bias current dominates the 1/f/sup 3/ close-in phase noise, even if the waveform symmetry has been assured. A first-order estimation of the tuning curve for MOS-varactor-tuned VCOs is provided. Based on this result, a simplified phase-noise model for double cross-coupled VCOs is derived. This model can be easily adapted to cover other LC-tuned oscillator topologies. The theoretical analyses are experimentally validated with a 0.25 /spl mu/m CMOS fully integrated VCO for 5 GHz wireless LAN receivers. By eliminating the bias current generator in a second oscillator, the close-in phase noise improves by 10 dB and features -70 dBc/Hz at 10 kHz offset. The 1/f/sup 2/ noise is -132 dBc/Hz at 3 MHz offset. The tuning range spans from 4.6 to 5.7 GHz (21%) and the current consumption is 2.9 mA.     

A figure of merit for a varactor-tuned microwave oscillator

This note derives a figure of merit for a varactor tuned microwave solid state oscillator. Thu figure of merit is in terms of electronic tuning range and power output normalized to the available power from the untuned oscillator. This enables the varactor which will give the required combination of thorns parameters to be specified in terms of y and f _c.

The figure of merit also shows that a varactor with a large value of the product yf _c maximizes the figure of merit.     

Theoretical and experimental investigation of novel varactor-tunedswitchable microstrip ring resonator circuits

A microstrip ring resonator circuit loaded with two p-i-n diodes has been developed for use as a switchable filter. By replacing one p-i-n diode with a varactor diode, the switchable filter can be made electronically tunable. Isolation exceeding 20 dB with 9% tuning bandwidth was demonstrated. An analysis based on transmission line theory was used to model both circuits. The analysis includes the effects of diode parasitics, coupling gaps, dispersion, and mounting-gap capacitance. The experimental results agree very well with the theoretical calculation     

A Wide Tuning Range Voltage Controlled Oscillator Using Common-Base Configuration and Inductive Feedback

Usually the tuning range of voltage controlled oscillator (VCO) is much narrower than the possible resonant frequency range of the tank at different tuning voltages. In this letter we analyze the traditional common-base type VCO, give a simple but useful insight about the mechanism behind the topology, and verified the conclusions with a 2 mum heterojunction bipolar transistor (HBT) VCO. The results show that with the CB configuration, proper feedback inductor and wide tuning range varactor, the tuning range can be almost the same as the resonant frequency range of the tank at different tuning voltages. A wideband voltage controlled oscillator using a commercial 2 mum HBT technology is designed, fabricated and measured. The varactor with wide range of capacitance is used to achieve 53.33% measured tuning range from 9.46 to 16.34 GHz. The measured phase noise at 1 MHz offset is between -90 and -102 dBc/Hz. The total chip size is 1 mm² including all testing pads, while the core area is 0.64 mm². The VCO is suitable for wideband application such as in measurement equipment or astronomical exploring telescopes.     

Analysis of Millimeter Wave Varactor-Tuned Gunn Oscillator Stabilized with a Transmission Cavity

A novel circuit architecture which describes millimeter wave varactor-tuned Gunn oscillator stabilized with a transmission cavity has been proposed in this paper. A corresponding equivalent circuit model has been presented in order to study its performance characteristics. The circuit model consists of four parts which are varactor cavity, main cavity, transmission waveguide and transmission cavity. Based upon this model, electrical tuning characteristics have been studied at first. Mode jumping problems during electrical tuning process have been analyzed qualitatively. Moreover, quality factor and efficiency of the circuit model have been derived by virtue of relevant circuit parameters. The effects of some important circuit parameters affecting circuit performance parameters have been discussed. The circuit model can describe the circuit architecture accurately and effectively. This circuit architecture, which can generate signals exhibiting low frequency modulation noise, high frequency stabilization and electrical tunable characteristics, is applicable to various practical situations.