Zhao Bohua

The realization of an SVGA OLED-on-silicon microdisplay driving circuit

An 800 × 600 pixel organic light-emitting diode-on-silicon (OLEDoS) driving circuit is proposed. The pixel cell circuit utilizes a subthreshold-voltage-scaling structure which can modulate the pixel current between 170 pA and 11.4 nA. In order to keep the voltage of the column bus at a relatively high level, the sample-and-hold circuits adopt a ping-pong operation. The driving circuit is fabricated in a commercially available 0.35 μm two-poly four-metal 3.3 V mixed-signal CMOS process. The pixel cell area is 15 × 15 μm2 and the total chip occupies 15.5 × 12.3 mm2. Experimental results show that the chip can work properly at a frame frequency of 60 Hz and has a 64 grayscale (monochrome) display. The total power consumption of the chip is about 85 mW with a 3.3V supply voltage.

A new OLED SPICE model for pixel circuit simulation in OLED-on-silicon microdisplay design

A new equivalent circuit model of organic-light-emitting-diode (OLED) is proposed. As the single- diode model is able to approximate OLED behavior as well as the multiple-diode model, the new model will be built based on it. In order to make sure that the experimental and simulated data are in good agreement, the constant resistor is exchanged for an exponential resistor in the new model. Compared with the measured data and the results of the other two OLED SPICE models, the simulated I -V characteristics of the new model match the measured data much better. This new model can be directly incorporated into an SPICE circuit simulator and presents good accuracy over the whole operating voltage.

An improved driving circuit scheme applied in extreme low-current design on OLED-on-silicon microdisplay

This paper describes an improved driving circuit scheme including a slew-rate enhancement circuit for organic light-emitting-diode-on-silicon (OLEDoS) microdisplay design. Due to the basic pixel cell area of OLEDoS microdisplay being less than 300 μm2, pixel currents are always needed to modulate from hundreds of pico-amperes (pA) to tens of nano-amperes (nA). The proposed circuit can satisfy the timing requirements (the time period of video sample signal is about 30ns) at such low current. Extra circuits introduced by the improved driving circuit scheme have a simple structure and consume little additional power in static condition.

Analysis and optimization of current sensing circuit for deep sub-micron SRAM

A quantitative yield analysis of a traditional current sensing circuit considering the random dopant fluctuation effect is presented. It investigates the impact of transistor size, falling time of control signal CS and threshold voltage of critical transistors on failure probability of current sensing circuit. On this basis, we present a final optimization to improve the reliability of current sense amplifier. Under 90 nm process, simulation shows that failure probability of current sensing circuit can be reduced by 80% after optimization compared with the normal situation and the delay time only increases marginally.