Extension of inductor voltage control to three-phase buck-typeAC-DC converter

A novel inductor voltage control (IVC) method capable of achieving near unity power factor is being proposed for buck-type AC-DC pulsewidth-modulated (PWM) converters. In this method, the input inductor voltages are kept within a hysteresis band about a sinusoidal template, thus ensuring sinusoidal input currents. This control method is much less sensitive to parameter and control variations than the existing delta modulation control (DMC) method. A companion paper has introduced the IVC method for the case of a single-phase buck-type converter. In the present paper, problems involved in direct extension of the IVC method to a three-phase buck converter are discussed first. Following this, a new switching logic scheme is proposed which enables these problems to be overcome and for IVC (as well as DMC) to be extended to a three-phase converter as well. Detailed simulation and experimental results have been provided to verify the expected good performance with IVC. The proposed IVC method has potential in applications such as those requiring AC-DC rectifiers with current limiting     

Micromechanical resonator with ultra-high quality factor

A 6.3 MHz Lame-mode square resonator with fully differential drive and sense electronics, exhibiting quality factor (Q) values over 1 million in ambient pressures as high as 200 Pa is reported. A maximum Q value of 1.6 million was experimentally measured for the resonator designed for this study. It was also experimentally observed that the Q value for the designed bulk mode resonator was relatively independent for pressures below 200 Pa, suggesting that the Q is pressure limited for pressure higher than 200 Pa.     

A CMOS Readout Circuit for SOI Resonant Accelerometer With 4-$mu rm g$ Bias Stability and 20-$ murm g/sqrt{{hbox{Hz}}}$ Resolution

A fully differential CMOS readout circuit for SOI resonant accelerometer is reported. The readout circuit is essentially an oscillator, consisting of an oscillator and a low noise automatic amplitude control (AAC) loop. A differential sense resonator is proposed to facilitate fully differential circuit topology and improves the SNR under a 3.3-V supply. A second-order AAC loop filter and a novel chopper stabilized rectifier are employed in the AAC loop to remove the noises, in particular, the 1/f noise, and to minimize the phase noise caused by the amplitude stiffening effect. The strong driving feedthrough is avoided by separating the drive and sense operation in the time domain, while using the same electrodes. The complete resonant accelerometer operates under a 3.3-V supply and achieves 140-Hz/g scaling factor, 20 mug/radicHz resolution and 4 mug bias stability. The readout circuit draws 7 mA under 3.3-V supply.     

Micromechanical resonators with submicron capacitive gaps in 2 μm process

An innovative gap reduction technique is reported to achieve sub-micron capacitive gaps for micromechanical resonators to boost the output signal using the standard low-cost 2 mum commercially available foundry process from MEMSCAP. Electrostatic actuation was used to reduce the gap size below the fabrication limitation. To demonstrate the proposed idea, a 6.35 MHz Lame-mode square resonator was designed, fabricated and tested. The resonator gap size was experimentally measured to be 0.64 mum, which boosted the resonance peak by 20 dB.     

Micromechanical oscillator circuits: theory and analysis

In this paper, detailed theoretical analysis of micromechanical Transresistance oscillator is presented. Analytical expressions are derived for the frequency pulling, critical transimpedance, maximum negative resistance, and start-up time constant of the Transresistance oscillator circuit which are useful for the design of micromechanical oscillators. These results are then used to study the frequency stability of Transresistance oscillator circuit and compare its operating conditions with that of the Pierce oscillator circuit which is widely used in micromechanical oscillators. The results conclusively show that the Transresistance oscillator has less start-up problems and better frequency stability than the Pierce oscillator. These results are then verified with a well-established circuit theory that compares the phase-frequency plots of the Pierce and Transresistance oscillator.     

Acoustic phonon characterisation of fixed-fixed beam MEMS switch

The reported work focuses on an acoustic phonon characterisation method for MEMS devices. This technique is uniquely suited to address challenges of MEMS device characterisation as a low cost and non-detechnique is uniquely suited to address challenges of MEMS device characterisation as a low cost and non-destructive method. The mechanical switching action of a fixed-fixed beam MEMS switch is characterised using this acoustic phonon characterisation technique and a correlation between phonon measurements and electrical waveforms is carried out. Insights on the mechanical state of the switch are also obtained using this acoustic phonon characterisation technique structive method. The mechanical switching action of a fixed-fixed beam MEMS switch is characterised using this acoustic phonon characterisation technique and a correlation between phonon measurements and electrical waveforms is carried out. Insights on the mechanical state of the switch are also obtained using this acoustic phonon characterisation technique.     

Effect of structural thickness, anchor length and number of anchors on performance of micromechanical bulk-mode resonators

The performance of micromechanical Lame′-mode square resonator designs with different geometric parameter variations in structural layer thickness, length of anchor beams and the number of anchors placed at nodal points, is reported. Measured results reveal that there is an optimal range of anchor designs that provide high quality factor (Q) above one million, along with low motional resistance, R_m. Two-anchor- only support design is able to achieve very high Q_s but results in higher motional resistance. Lower structural thickness generally reduces the quality factor Q and R_m owing to interference from out-of- plane modes.     

Multiwall carbon nanotube resonator for ultra-sensitive mass detection

The experimental realisation of a multiwall carbon nanotube (MWNT) resonator for mass sensing applications is reported. Fabricated MWNT resonators with length, inner radius and outer radius as 34.37 μm, 5.37 nm and 13.27 nm, respectively, had a measured resonant frequency around 110?120 kHz. Measured results indicate that these MWNT resonators exhibit sub-attogram reponsivity.     

Inductor voltage control of buck-type single-phase AC-DC converter

A novel inductor voltage control (IVC) method cable of achieving any input power factor including unity is being proposed for buck-type AC-DC pulsewidth modulation (PWM) converters. In this method, the input inductor voltage is kept within hysteresis band about a sinusoidal template, thus ensuring sinusoidal input current. This control is much less sensitive to parameter and control signal changes than the existing delta modulation control (DMC). In this paper the IVC method is applied to single-phase buck-type converter. Useful design results based on steady-state analysis have been presented. Simulation and experimental results have been provided to verify the theoretical results. The companion paper extends the applicability of the IVC control method to three-phase converters also. The proposed IVC method has potential in applications requiring AC-DC rectifiers with over-current/short-circuit current limit