What is the power consumption of a 1.33 inch Sharp Memory TFT?
The power consumption of a 1.33 inch Sharp Memory TFT is exceptionally low, typically drawing less than 1 microwatt (µW) when displaying a static image. This is a fundamental characteristic of Memory LCD technology, which is distinct from standard TFT or OLED displays. Unlike conventional displays that require constant power to refresh pixels, a Sharp Memory TFT retains its image state without any power draw. The only significant power consumption occurs during the image update process, where the display draws a brief burst of current. For a typical 1.33 inch 128x128 resolution panel, the active power during a full-screen refresh is around 0.5 to 1 milliwatt (mW), but this lasts for only a few milliseconds. In practice, for applications that update the screen infrequently, such as a smartwatch, e-reader, or industrial sensor display, the average power consumption can be as low as 2 to 5 microwatts. This makes it one of the most power-efficient display options available for battery-powered devices.
To understand the specifics, let's break down the power consumption metrics for the 1.33 inch sharp memory tft display. The display module operates at a typical supply voltage of 3.3V, with a range of 2.5V to 3.6V. The static current consumption, when the display is not being updated, is essentially zero. Sharp's datasheets for similar Memory LCD panels, such as the LS013B7DH03, specify a static current of 0.1 µA or less. At 3.3V, this translates to a static power consumption of 0.33 µW. During a refresh cycle, the display draws a current of approximately 150 to 200 µA for a duration of 10 to 20 milliseconds. This burst current results in an active power of about 0.5 to 0.66 mW. However, because the refresh is so brief, the average power consumption is dominated by the refresh frequency.
Let's consider a practical scenario. If you update the display once every 10 seconds, the active power is only active for 15 milliseconds per refresh. The average power consumption can be calculated as follows:
Active energy per refresh: 0.66 mW * 0.015 seconds = 9.9 microjoules (µJ).
Over 10 seconds, the average power is 9.9 µJ / 10 s = 0.99 µW.
Add the static power of 0.33 µW, and the total average power is approximately 1.32 µW.
This is an order of magnitude lower than even the most efficient e-paper displays, which often require a few milliwatts for updates. For comparison, a standard 1.3 inch OLED display, even when showing a static image, can consume 10 to 20 mW due to the need to power the organic light-emitting layers. A standard TFT LCD with a backlight can consume 50 to 100 mW or more. The Sharp Memory TFT, by contrast, uses a reflective technology that requires no backlight, and its memory-in-pixel architecture eliminates the need for constant refreshing.
The pixel structure of the Sharp Memory TFT is what enables this low power. Each pixel contains a 1-bit memory cell (SRAM) that stores the state of the pixel. When the display is updated, the controller sends a signal to each pixel, and the memory cell latches the new state. Once latched, the pixel remains in that state without any further power. This is fundamentally different from a standard TFT, where each pixel is a capacitor that leaks charge and must be refreshed at 60 Hz or more. The Sharp Memory TFT also has a very low refresh rate requirement—typically 1 Hz or less for static images—which further reduces power.
Data from Sharp's application notes for the 1.33 inch panels indicate that the total power consumption for a full-screen update at 60 Hz (which is not typical but possible) is about 1.5 mW. However, running at 60 Hz defeats the purpose of the memory technology. In most real-world applications, the refresh rate is set to 1 Hz or lower. For example, in a smartwatch that updates the time every second, the average power is around 5 to 10 µW. In a temperature sensor display that updates every minute, the average power can drop to less than 1 µW.
Another factor is the interface. The 1.33 inch Sharp Memory TFT uses a serial interface (SPI) for communication. The SPI bus itself consumes power during data transfer, but this is negligible compared to the display's own power draw. The typical SPI clock frequency is 1 to 10 MHz, and the data transfer for a 128x128 frame (16,384 pixels) is about 2 KB. At 10 MHz, this transfer takes about 1.6 milliseconds, and the power consumption of the SPI interface on the microcontroller side is typically in the range of 0.1 to 0.5 mW during that burst. However, this is still a small fraction of the overall system power.
Let's look at a detailed comparison table to illustrate the power advantages:
| Display Type | Static Power (µW) | Active Power (mW) | Refresh Rate (Hz) | Average Power (µW) at 1 Hz Update |
|---|---|---|---|---|
| 1.33 inch Sharp Memory TFT | 0.3 | 0.66 | 1 | 1.0 |
| 1.3 inch OLED | 10,000 | 15 | 60 | 10,000 |
| 1.3 inch TFT with Backlight | 50,000 | 100 | 60 | 50,000 |
| 1.5 inch E-Paper | 0 | 15 | 0.001 | 15 |
As the table shows, the Sharp Memory TFT consumes about 10,000 times less power than an OLED for static images, and 50,000 times less than a standard TFT with backlight. Even compared to e-paper, which also has zero static power, the Sharp Memory TFT is more efficient during updates because the update time is much shorter (milliseconds vs. seconds for e-paper).
The implications for battery life are significant. A device powered by a 100 mAh lithium coin cell battery, for example, could run a Sharp Memory TFT for over 10 years if the display is updated once per minute. In contrast, the same battery would power an OLED for only about 10 hours. This makes the 1.33 inch Sharp Memory TFT ideal for applications like digital price tags, medical devices, remote controls, and IoT sensors where battery life is critical.
One important nuance is that the power consumption depends on the amount of data being updated. A partial update, where only a small region of the screen changes, consumes proportionally less power because only the pixels in that region are refreshed. The Sharp Memory TFT supports partial updates, which can further reduce power. For example, updating a 16x16 pixel icon instead of the full 128x128 screen reduces the active power by a factor of 64, resulting in an average power of less than 0.1 µW for infrequent updates.
The operating temperature also affects power consumption. The Sharp Memory TFT is specified for operation from -20°C to +70°C. At lower temperatures, the internal resistance of the pixel memory cells increases slightly, which can increase the current draw during refresh by about 10-20%. However, the static power remains essentially zero. At high temperatures, the leakage current in the memory cells may increase, but this is still negligible—typically less than 1 µA at 70°C.
Another factor is the voltage level. The display can operate at 2.5V, which reduces the active power to about 0.38 mW (150 µA * 2.5V). However, the SPI interface may require 3.3V for reliable communication, so a voltage regulator might be needed. The efficiency of the regulator should be considered in the overall system power budget. A good low-dropout regulator (LDO) can achieve 90% efficiency, so the total power from the battery might be about 10% higher than the display's own consumption.
For developers, the 1.33 inch sharp memory tft display is available as a module with an integrated driver IC (typically Sharp's own driver). The module includes a flexible PCB with a connector for easy integration. The driver IC handles the serial interface and the pixel refresh logic, so the microcontroller only needs to send the image data. The driver IC itself consumes about 0.1 µW in standby mode, which is included in the static power figure.
In terms of practical implementation, the power consumption can be measured using a precision current meter. A typical test setup with a 3.3V supply and a 1 Hz update rate shows a current draw of 0.3 µA average, which is about 1 µW. This is consistent with the datasheet specifications. For a more aggressive power-saving strategy, the display can be put into a deep sleep mode where the driver IC is turned off, but this requires the microcontroller to reinitialize the display on wake-up, which adds a small overhead.
For a detailed product specification and to purchase the module, you can refer to the 1.33 inch sharp memory tft display product page, which provides the full datasheet, interface timing, and example code for various microcontrollers.
The low power consumption of the Sharp Memory TFT also makes it suitable for energy harvesting applications. A small solar cell or a thermoelectric generator can provide enough power to update the display a few times per day. For instance, a 1 cm² solar cell in indoor light can generate about 10 µW, which is more than enough to power the display for a few updates per hour. This opens up possibilities for self-powered displays in remote or inaccessible locations.
One common misconception is that the Sharp Memory TFT is the same as an e-paper display. While both are reflective and have low power, the Sharp Memory TFT has a much faster update time (10-20 ms vs. 1-3 seconds for e-paper) and a higher contrast ratio (typically 10:1 vs. 7:1 for e-paper). The Sharp Memory TFT also supports multiple colors (black, white, and red in some variants), but the 1.33 inch version is monochrome (black and white). The viewing angle is excellent, at 160 degrees, which is comparable to standard TFTs.
The display's resolution of 128x128 pixels at 1.33 inches gives a pixel density of about 135 PPI, which is sufficient for text and simple graphics. The pixel pitch is 0.21 mm, which is fine enough for readability. The display is also very thin, at about 1.2 mm, and lightweight, at about 5 grams, making it suitable for wearable devices.
In terms of cost, the 1.33 inch Sharp Memory TFT is more expensive than a standard TFT of the same size, typically costing $10 to $15 per unit in small quantities. However, the cost is justified by the extreme low power and long battery life, which can reduce the overall system cost by eliminating the need for large batteries or frequent battery replacements.
For developers, the key takeaway is that the power consumption of the Sharp Memory TFT is dominated by the refresh rate. To achieve the lowest power, you should minimize the number of updates and use partial updates when possible. The display is ideal for applications that require a static image most of the time, with only occasional updates. This includes digital clocks, weather stations, asset tags, and medical monitors.
One more technical detail: the display uses a 1-bit per pixel color depth, meaning each pixel is either black or white. This limits the display to monochrome images, but it also simplifies the driver and reduces the data transfer size. The grayscale can be simulated using dithering, but this increases the update frequency and thus power consumption. For most applications, the monochrome display is sufficient.
The display's memory-in-pixel architecture also has a unique feature: the image is retained even when the power is completely removed. This is because the memory cells are SRAM-based, which is volatile but holds the state as long as the display is powered. However, if the power is removed, the memory cells lose their state, and the display goes blank. This is different from e-paper, which retains the image without power. For the Sharp Memory TFT, the power must be maintained to keep the image, but the power draw is so low that it's effectively negligible.
In a battery-powered device, the microcontroller can be put into deep sleep between updates, and the display can be powered continuously. The total system power is then the sum of the display's static power (0.3 µW) and the microcontroller's deep sleep power (typically 1-5 µW for a low-power MCU like the STM32L0 or MSP430). This results in a total system power of about 2-5 µW, which can provide years of battery life from a small coin cell.
For those looking to integrate the display, the SPI interface is straightforward. The display requires 4 pins: CS (chip select), SCLK (serial clock), MOSI (master out slave in), and a command/data pin. The display also has a VCOM pin that needs to be driven with a square wave at 60 Hz to prevent DC bias on the pixels. This VCOM signal can be generated by the microcontroller or by an external oscillator. The power consumption of the VCOM driver is about 0.1 µW, which is already included in the static power figure.
In summary, the power consumption of a 1.33 inch Sharp Memory TFT is among the lowest of any display technology, with average power in the microwatt range for typical use cases. This is achieved through a combination of memory-in-pixel architecture, reflective technology, and low refresh rates. The display is ideal for applications where battery life is paramount, and its performance is well-documented in datasheets and application notes. The product page for the 1.33 inch sharp memory tft display provides further details on specifications, interface, and ordering information.