Overdrive Technique Research Articles

Fast response polymer stabilized blue phase by overdrive technique

A method that exploits an overdrive technique is demonstrated to realize fast rise times in devices using the polymer-stabilized blue phase (PSBP). The results indicated that the rise time of such devices can be improved dramatically by increasing the overdrive voltage because the double cylinder structure of PSBP in the device undergoes a strong torque from this voltage. However, a stable transmittance was not obtained when the overdrive voltage was applied for durations exceeding the time required to reach maximum transmittance. By optimizing the overdrive waveform, the rise time of the PSBP device was 80 μs, which was nine times faster than that with a pulse waveform. This result is expected to find use in liquid crystal display applications and phase shifter applications in which high responses are wanted.

Dynamic response of ferrofluidic deformable mirrors using elastomer membrane and overdrive techniques

The experimental results obtained with a ferrofluidic deformable mirror controlled by electro-magnet actuators are presented here. Using a step input through a single actuator, we obtained a steady-state settling time of 100 ms; however, different combinations of overdrive inputs can be used to decrease it to 25 ms. A new technique which consists of laying down an elastomer membrane, coated with an aluminum film, on the ferrofluid is also discussed. By adding the membrane on the ferrofluid, it further decreases the time response by a factor of 2. Furthermore, the thin aluminum layer improves the reflectivity of the mirror. Finally, using the membrane and the overdrive techniques combined, the time response is improved by a factor of 20. Numerical simulations show that ferrofluidic mirrors using membranes and improved electronics should reach settling times of the order of a millisecond. Presumably, even lower settling times could be possible.

The high-power operation of a terahertz free-electron laser based on a normal conducting RF linac using beam conditioning

The feed-forward control of the amplitude and phase of a high-power RF pulse based on the overdrive technique is applied to an L-band electron linac to ensure that the energy of the electron beam is uniform and constant enough for the recommissioning of a terahertz (THz) free-electron laser (FEL) at the Institute of Scientific and Industrial Research (ISIR), Osaka University. The quality of the electron beam is evaluated using the time-resolved measurement of its energy spectrum; the energy is constant within 0.1% during the electron macropulse for 15MeV energy except for the transient period in the leading edge. A high-power, stable FEL operation that reaches saturation is obtained using beam conditioning. The characteristics and performance of the FEL for THz radiation are measured at the end of an evacuated transport line. The frequency ranges from 2 to 12THz, from 25 to 150μm in wavelength, and the maximum energy in the FEL macropulse with a ~3μs duration is 3.7mJ at 67μm; using these values, the peak power in the macropulse is calculated to be 1.2kW, while that in the micropulse with a 20ps duration is calculated to be 0.5MW. These values are comparable to those in the THz range of other FELs that are based on normal conducting RF linacs.

Feed-forward control of the amplitude and the phase of a high-power RF pulse based on the overdrive technique

We have developed a new feed-forward control system to precisely control the amplitude and phase of the pulsed RF power in an electron linear accelerator (linac) to make the accelerating field constant. Fast variations and ripples in the amplitude and the phase in RF pulses of some-microsecond duration are compensated for by applying anti-variation control signals to a variable attenuator and a phase shifter in the low-level system. The system makes use of the overdrive technique, which is commonly used in analog circuits, to speed up the slow response of the analog phase shifter, while the control signals are digitally processed; thus, the method is a hybrid of analog and digital techniques. Peak-to-peak variations in the amplitude and phase are reduced by these means from 11.6% to 0.4% and from 6.1° to 0.3°, respectively, in 7.6-μs-long RF pulses for the L-band electron linac at Osaka University.

A Scalable Shield-Bitline-Overdrive Technique for Sub-1.5 V Chain FeRAMs

A ferroelectric capacitor overdrive technique with shield-bitline drive has been demonstrated and verified by a 130 nm 576 Kb test chip with a 0.7191 μm2 cell. First, cell signal degradation and bitline-to-bitline coupling noise worsened by wide cell signal distribution in low voltage scaled FeRAMs are discussed. Next, the shield-bitline-overdrive technique is presented. This technique applies a 0.24 V higher bias to the ferroelectric capacitor through bitline-to-bitline coupling during the read operation without increasing device stress, and eliminates bitline-to-bitline coupling noise. The measured tail-to-tail cell signal is improved by 100 mV and effectively doubles for 1.3 V array operation. The area penalty of the proposed scheme is 0.9% of the 576 Kb cell array, and the access time penalty is 5 ns. The effect of this technique will be enhanced by cell shrink as the bitline-to-bitline coupling ratio increases. A tail-to-tail cell signal window of more than 200 mV is expected in 1.3 V 256 Mb and 1.2 V 512 Mb chain FeRAMs, whereas the tail-to-tail cell signal window without overdrive would degrade to 95 mV for 256 Mb and 60 mV for 512 Mb.

New and efficient dynamic capacitance compensation (DCC) system to reduce data size and artifacts for 120Hz Full-HD LCD panel

Although the overdrive technique is one of the most effective techniques for reducing motion blur artifact in liquid crystal displays (LCD), it requires considerable frame memory (more than one frame). Artifacts can be reduced significantly when more frames are used for overdrive technology. This paper introduces a new and efficient dynamic capacitance compensation (DCC) system to reduce motion blurring as well as other artifacts, such as overshoot and rising bounce using 3 frames. The main idea of the proposed system is to use 3 frames using motion estimation for the overdrive of a 120Hz Full-HD LCD panel. To evaluate the performance of the proposed method, the quantitative measures were defined in terms of the peak signal-to-noise (PSNR) and data reduction ratio. The experimental results showed that proposed algorithm could reduce data size significantly (~90%), and the resulting images had sufficient quality (average 34.68dB) for overdrive in the LCD panel. Therefore, the proposed approach can be a useful tool for reducing the frame data size of the LCD overdrive technique as well as artifacts, such as motion blurring, overshoot and rising bounce.

Temperature compensated overdrive in vertically aligned liquid crystal displays

The occurrence of backflow in vertically aligned liquid crystal displays (VA-LCDs) inhibits application of conventional overdrive techniques to achieve faster switching. This (hydro)dynamic behavior is simulated accurately by using the Leslie–Ericksen theory in a one-dimensional model. Taking the limitations due to backflow into account from these simulations, we designed overdrive schemes for VA-LCDs. The temperature sensitivity of a fixed overdrive table was eliminated by adapting the scheme to the simulated temperature variations in the dynamic behavior. Experimental verification in the 25–75 °C range shows that the resulting temperature compensated overdrive leads to faster switching, which is expected to be artifact free.

Vector quantizer based block truncation coding for color image compression in LCD overdrive

The overdrive technique has been popularly used to alleviate the motion blur on liquid-crystal display (LCD) by shortening the response time of the liquid crystal. However, this technique requires a large frame buffer to store the previous frame as a reference. In this paper, we propose a novel block truncation coding based on the vector quantizer for the color image compression in LCD overdrive. Due to the constant output bit-rate and the low computational complexity, the proposed method is suitable for the hardware implementation in LCD overdrive. Experimental results show that the proposed method achieves higher compression ratio as well as better visual quality as compared with the conventional methods.

Software‐processed edge‐ and level‐adaptive overdrive (SELAO) method for high‐quality motion pictures

Abstract— In this paper, a software‐processed edge‐ and level‐adaptive overdrive (SELAO) method, which is a novel overdrive technique that utilizes not only a temporal change of gray levels but also a spatial edge intensity of motion pictures, is proposed. The SELAO method is a software video‐processing technology to improve motion‐picture quality rendered on LCDs more than is possible with a conventional SLAO method without edge‐adaptive overdrive, and it works in real time on commonly used personal computers (PCs).

An Organic FET SRAM With Back Gate to Increase Static Noise Margin and Its Application to Braille Sheet Display

An integrated system of organic FETs (OFETs) and plastic actuators is proposed, and it is applied to a Braille sheet display. Some circuit technologies are presented to enhance the speed and the lifetime for the Braille sheet display. An OFET SRAM is developed to hide the slow transition of the actuators. Developed five-transistor SRAM cell reduces the number of the bit lines by one-half and reduces the SRAM cell area by 20%. Pipelining the write-operation reduced the SRAM write-time by 69%. Threshold voltage control technology using a back gate increased the static noise margin of SRAM and compensated for the chemical degradation of the OFETs after 15 days. The oscillation frequency tuning range from -82% to +13% in a five-stage ring oscillator is also demonstrated with the threshold voltage control technology. The overdrive techniques for the driver OFETs reduced the transition time of the actuator from 34 s to 2 s. These developed circuit technologies achieved the practical 1.75-s operation to change all 144 Braille dots on Braille sheet display and will be essential for the future large area electronics made with OFETs

46.3: Software-Processed Edge- and Level-Adaptive Overdrive (SELAO) Method for High-Quality Motion Picture

We have developed the software-processed edge- and level-adaptive overdrive (SELAO) method. The SELAO method is a novel overdrive technique that utilizes not only the temporal change of the gray level but also the spatial edge intensity of the motion picture. The SELAO software can work in real time on PCs. Therefore, the SELAO method can improve the motion picture quality of an LCD more than the conventional SLAO method without edge-adaptive overdrive.

46.1: UV‐Stable High‐Birefringence Low‐Viscosity Isothiocyaniane Liquid Crystals and Application to 50‐μsec Response Switching Device

AbstractUV stable, high birefringence and low viscosity nematic liquid crystal mixtures were developed and their properties evaluated. Our new mixtures exhibit similar birefringence but ∼3.5X lower visco‐elastic coefficient than Merck E44. In the mean time, our new mixtures show better UV stability than those cyano‐biphenyls based commercial mixtures. To make a performance of new material more visible a high birefringence and relatively low viscosity liquid crystal mixture was developed for this experiment in conjunction with the voltage overdrive and undershoot technique. We demonstrated a liquid crystal light switch with response time ∼50 μs at room temperature and λ= 633 nm Potential application for sub‐millisecond laser beam steering is emphasized.

LP‐13: Late‐News Poster: A Study of Motion Adaptive CODEC Feedforward Driving without SDRAM

AbstractAuthors have been engaged in the development of a feed forward driving technique, as part of the overdrive technique to improve the response time of liquid crystal displays. They have developed, in particular, a compression feed forward driving system in which an image compression technique was applied, focusing on a method of reducing the frame memory necessary for the signal processing of overdrives. Further, they are now studying motion adaptive CODEC feed forward driving that reduces the amount of overdrive errors by adding a motion‐adaptive process to the image decoding section in cFFD. This paper discusses macFFD that does not use SDRAM as the overdrive for entry model LCD TVs. Setting the image compression ratio to 1/10 or so will enable the fabrication of frame memory for overdrive for SDTV using SRAM.

FLC microdisplays

Microdisplays made from ferroelectric liquid crystals (FLCs) and silicon integrated circuits offer exceptionally high resolutions along with the capability for single-panel sequential color. The binary pixels of these microdisplays are capable of full gray scale through the use of techniques that involve illumination modulation, subpixelation, and temporal dither. Continuous, DC-balanced display, even with the polarity-sensitive response of the FLC, can be achieved by using an electro-optic contrast inverter; alternately, image sticking can be minimized by specialized overdrive techniques that periodically toggle all the pixels.