# Reducing the Power Consumption of VR Displays with a Field Sequential Color LCD
## 3 Simulation Results  
For VR displays, single domain LCDs may be sufficient because of the narrow collection cone (\(\sim\)20\({}^{\circ}\)) limitation of human eyes. Therefore, we chose a single domain FFS LCD because of its wide viewing angle and weak color shift. Color sequential display relies on the human vision system to integrate three successive (RGB) images into a color image. For this reason, the LC response time should be fast enough, depending on the required frame rate. Variable frame rates are employed for different tasks. For example, the Meta Quest Pro features a 90 Hz maximum refresh rate (72 Hz mode available) targeted for office tasks. Games and videos may require a higher frame rate, e.g., 120 Hz. For this reason, the virtual wall [24,25] is employed to further decrease the response time and achieve a color subframe of 270 Hz or 360 Hz. To determine the appropriate electrode width and gap, we employed TechWiz LCD 3D (Sanayi, Korea) to simulate the voltage-dependent transmittance and average gray-to-gray (GTG) response time, corresponding to a series of different electrode widths and gaps. The simulation conditions include a 2\({}^{\circ}\) pretilt angle and 0\({}^{\circ}\) rubbing angle. The cell gap is 2 \(\upmu\)m, which helps decrease response time and crosstalk while maintaining a good manufacturing yield. The pixel pitch \(L\) = 6 \(\upmu\)m, has recently been realized [26]. Figure 5 shows that finer electrode widths (\(w\)) or gaps (\(g\)) help decrease the response time. For example, \(w\) = 1.5 \(\upmu\)m and \(g\) = 1.5 \(\upmu\)m can achieve an average GTG response time less than 3.7 ms (top horizontal dashed lines) at \(T\) > 22 \({}^{\circ}\)C and 2.7 ms (bottom horizontal dashed lines) at \(T\) > 30 \({}^{\circ}\)C; the latter can support 72 Hz framerate (or 216 Hz color subframes). As \(T\) increases, the average GTG response time decreases rapidly because of the decreased viscosity. Table 1 lists the rise time and decay time corresponding to different gray levels at 50 \({}^{\circ}\)C. To calculate the GTG response time, the voltage-dependent transmittance curve is uniformly divided into 256 gray levels. The response time between 0, 64, 128, 192, and 255 gray levels is then obtained by calculating the transition time between 10% and 90% transmittance change. The fastest GTG response time is 0.62 ms and the average GTG response time is 1.5 ms, which leaves more time for the thin film transistor (TFT) gate lines to be scanned (\(\sim\)1 ms corresponding to 360 Hz color subframe or \(\sim\)2 ms corresponding to 270 Hz color subframe). The remaining time (\(\sim\)0.3-0.5 ms) is used for turning on the backlight and obtaining low motion picture response time. According to the time slots assigned for pixel addressing, LC response, and backlight flashing, the duty cycle is calculated to be \(\sim\)10%. It is noted that faster scanning time can be achieved using multiple integrated circuits (ICs) that simultaneously scan the gate lines [27]. To write data for several (\(n\)) gate lines in different blocks synchronously, the number of data lines is inevitably increased by  
Figure 5: Simulated temperature-dependent average GTG response times at different electrode widths and gaps. \(n\) times. Fortunately, the data lines can be reduced by 3\(\times\) because of the color sequential display. In this manner, the time for pixel addressing can be greatly reduced by \(n\) times. Overdrive and undershoot can be further employed to achieve sub-millisecond response times for LCs, alleviating the time for pixel addressing and enabling a fast response time for lower temperature operation, but the driving circuitries are more complicated. Despite a fine electrode pitch, Figure 6 shows that a relatively low threshold voltage of ~1.6 V\({}_{\text{rms}}\) is obtained, arising from a decent dielectric anisotropy. The normalized transmittance for red, green, and blue (RGB) wavelengths almost saturates at 6 V\({}_{\text{rms}}\), where the transmittance of 52% is achieved at \(\lambda\) = 450 nm.