Output Frequency Stability Research Articles

Low power, low voltage on chip relaxation oscillator

ABSTRACTA low power, low voltage resistor-capacitor or relaxation oscillator circuit is proposed. The proposed relaxation oscillator works with minimum 1.1 V supply and consumes less than 3 uA average current for 128 KHz output frequency. A novel integrated comparator and bias current reference circuit ensures low current consumption and low silicon area while providing good output frequency stability across voltage and temperature variation. Capacitor trimming is used to tune the output frequency across process variation. The proposed circuit is designed in 40 nm complementary metal oxide semiconductor process and simulation and silicon measurement results are provided to show the functionality.

Rotational piezoelectric wind energy harvesting using impact-induced resonance

To improve the output power of a rotational piezoelectric wind energy harvester, impact-induced resonance is proposed to enable effective excitation of the piezoelectric cantilevers' vibration modes and obtain optimum deformation, which enhances the mechanical/electrical energy transformation. The impact force is introduced by forming a piezoelectric bimorph cantilever polygon that is fixed at the circumference of the rotating fan's internal surface. Elastic balls are placed inside the polygon. When wind rotates the device, the balls strike the piezoelectric cantilevers, and thus electricity is generated by the piezoelectric effect. The impact point is carefully chosen to use the first bending mode as much as possible, and thus maximize the harvesting efficiency. The design enables each bimorph to be struck in a similar area and every bimorph is struck in that area at different moments. As a result, a relatively stable output frequency can be obtained. The output frequency can also be changed by choosing different bimorph dimensions, which will also make the device simpler and the costs lower. A prototype piezoelectric energy harvester consisting of twelve piezoelectric cantilevers was constructed. The piezoelectric cantilevers were made from phosphor bronze, the lead zirconium titanate (PZT)-based bimorph cantilever had dimensions of 47 mm × 20 mm × 0.5 mm, and the elastic balls were made from steel with a diameter of 10 mm. The optimal DC output power was 613 μW across the 20 kΩ resistor at a rotation speed of 200 r/min with an inscribed circle diameter of 31 mm.

Investigation of Phase-Shifting and Frequency Conversion Sinusoidal Signal Generator Based on DDS and FPGA

The direct digital frequency synthesis (DDS) technology has high frequency resolution, fast frequency switching, low phase noise and higher frequency stability, so it is widely used in communications, aerospace, instrumentation and other fields. In this paper, the DDS system was designed based on Field Programmable Gate Array (FPGA) and hardware design language (VHDL). The experimental and simulation results show that the system has stable output frequency, high frequency accuracy, adjustable frequency and phase.

An autonomous impact resonator with metal beam between a pair of parallel-plate electrodes

This paper reports an autonomous impact resonator with a metal beam fixed on an insulated base between a pair of parallel-plate electrodes. The beam can be excited to impact the positive and negative electrodes alternately and maintain oscillation only by DC input. Compared with previous autonomous impact resonators, this resonator can achieve stable frequency output without causing harmful electrical breakthrough of the circuit. Besides that, the motion trajectory of the beam can be tunable by adjusting the electrodes placement. As such, the resonator is very attractive for future micro sensors and actuators applications, especially for actuators of micro flapping robots.

A High PSRR, Low Temperature Coefficient Bandgap Reference Circuit for Step-Down DC-DC Converters

A high power supply rejection ratio (PSRR), low temperature coefficient (TC) bandgap reference (BGR) circuit for step-down DC-DC converters is presented in this paper. Implemented in 0.5μm BCD technology, the PSRR of the proposed reference is nearly 110dB at low frequency, 40dB at 100 kHz, and 30dB at 1MHz. The temperature coefficient can be lower than 10ppm/oC with temperature ranging from 0 to 100oC by implementing an advanced high-order temperature compensation technique. Furthermore, temperature compensation method is also adopted to decrease the temperature coefficient of the output current, so that the oscillator in the converter can achieve a much more stable output frequency. All the improvements listed above are based on the smallest area sacrifice.

A Highly Integrated 1.8 GHz Frequency Synthesizer Based on a MEMS Resonator

A highly integrated 1.7-2.0 GHz digitally programmable frequency synthesizer using a MEMS resonator as its reference is presented. Due to the dimensions of the MEMS device (e.g., 25 mum by 114 mum), the entire system with a total area of 6.25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> can be housed in a small standard chip package. This considerably reduces the form factor and cost of the system, compared to using an external crystal as a reference. The MEMS resonators are clamped-clamped beams fabricated using a CMOS-compatible process. The main structural layer is made of silicon carbide, which provides the resonators with higher power handling capabilities and higher operating frequencies, compared to silicon. The resonators are electrostatically and thermally tunable - an 8.4% frequency tuning is demonstrated for a 9 MHz resonator. The 100 nm vertical transducer gaps of the resonators allow the use of electrostatic actuation voltages as low as 2 V. An integrated high gain-bandwidth trans-impedance amplifier (TIA) is combined with a resonator to generate the synthesizer's input reference signal. The TIA employs automatic gain control to mitigate the inherent low power handling capabilities and the non-linearities of the MEMS device, thus minimizing their effect on phase noise. The fractional- N synthesizer employs a 3rd-order 20-bit delta-sigma modulator to deliver a theoretical output resolution of ~ 11 Hz, in order to allow for high output frequency stability when used with an appropriate feedback loop. A fully integrated on-chip dual path loop filter is used to maintain a high level of system integration. With a supply voltage of 2 V, the phase noise for a 1.8 GHz output frequency and a ~12 MHz reference signal is -122 dBc/Hz at a 600 kHz offset, and -137 dBc/Hz at a 3 MHz offset.

Relative Frequency Calibration for Fast Frequency Sweep Microwave Reflectometry

A frequency-modulated reflectometer with a frequency band of 26.5 to 40 GHz has been constructed and installed in the TST-2 spherical tokamak to measure fast density profile evolution. In order to calibrate the instantaneous frequency for various frequency sweep rates, a waveform matching method has been proposed and applied to the reflectometer. This method compares the interference patterns (i.e., waveforms) of a fixed target reflection, which do not depend on the sweep rate, and obtains the instantaneous frequency by fitting the target waveform time to the time for a reference sweep waveform. This allows evaluation of output frequency stability. The overall frequency error, including reproducibility, is around 0.1 GHz. Sweep rates up to 20 μs were used to measure the density profile evolution during rf heating.

Development of an Oscillation Loop for a Micromachined Differential Type Resonant Accelerometer and Its Performance

This paper presents a surface micro-machined differential resonant accelerometer (DRXL) by using the epitaxially grown thick polysilicon process. The proposed DRXL utilizes the electrostatic stiffness changing effect of an electrostatic torsional actuator. This device produces a differential digital output proportional to an applied acceleration. For a self-generated and self-sustained oscillation of the resonator, a feedback oscillation loop is designed, implemented, and applied to the DRXL chip. The oscillation loop is designed using an analytical result based on the describing function method. Using the implemented self-sustaining oscillation loop, pecifications of sensor performance are obtained by various performance tests. These results show quite an improved quality factor and resolution compared to that of the sensing device only. And we obtained more stable output frequency responses.

A phase-shifting PLL frequency offsetter

A phase-shifting PLL frequency offsetter has been developed for use in the comparison of near-equal frequencies by phase-time recordings. The input frequency is shifted by means of a phase-shifting phase-locked loop. Time-linear phase shifting is simply obtained by inserting an RC link in the loop. Continuous operation is obtained by polarity switching of the capacitor and the phase detector at suitable phase values. An experimental circuit working around 114 kHz is presented, providing offset frequencies in the range 1 mHz to 10 Hz. The circuit uses eight analogue ICs. The output frequency stability depends on the input frequency stability, the fractional frequency offset and the stability of the analogue circuit, and is, for the circuit presented, a few parts in 1010 at an offset frequency of 0.01 Hz if the input frequency is based on a Cs or Rb source. The method can be used for frequencies up to the MHz range.

A High-Stability Low-Offset Phase-Locked-Loop Frequency Synthesizer

Small offsets in frequency from a given reference can be generated in a single sideband mixer employing a PLL. It is shown that the output frequency stability depends linearly on the fractional shift of the offset frequency generated, and on the coherence of the VCO. For the typical digital phase-locked loop synthesizer techniques, employing a crystal-stabilized VCO at 5 MHz, a 500-Hz offset can be realized with a 1-s frequency stability no better than a few parts in 107. An improved design is described which employs a pair of analog multipliers as an instantaneous phase detector together with feedback in quadrature. In laboratory tests this design demonstrated one second frequency stability of better than 1 part in 1010 when synthesizing the frequency 4.9995776 MHz from a 5.0-MHz cesium reference.

A Static Variable-Frequency Three-Phase Source Using the Cycloconverter Principle for the Speed Control of an Induction Motor

This paper describes a variable-frequency source employing the cycloconverter principle. SCR's have been used as the principal switching and voltage-regulating devices. The logic of the firing circuit has been discussed. The factor affecting output frequency stability has also been presented. A three-phase variable low-frequency oscillator has been used as the reference to achieve the variation of frequency. Voltage variation has been affected by phase delaying of the firing pulses in a manner similar to that in a phase-controlled rectifier. Provision has been made for changing the phase sequence at the output in order to facilitate reversal of the direction of rotation of the motor. Experimental results include output waveforms of various frequencies (0-30 Hz), and speed variations of the experimental motor (1 hp, 100 V, 1700 r/min) in either direction of rotation thereby providing the practical feasibility of the SCR cycloconverter for speed control of induction motors.