What is the refresh rate of a 1.33 inch Sharp Memory TFT?
The refresh rate of a 1.33 inch Sharp Memory TFT display is not a fixed single number like a standard LCD or OLED panel. Instead, it operates with a static refresh mechanism that fundamentally changes how we measure "refresh rate." For the 1.33 inch sharp memory tft display, the typical full-screen update time is around 20 to 30 milliseconds when writing new data to the entire 128x128 pixel array. This translates to an effective full-screen refresh rate of approximately 33 to 50 Hz if you were to continuously update the entire display. However, the key distinction is that the display uses memory-in-pixel (MIP) technology, meaning each pixel retains its state without power. So, once an image is written, the refresh rate drops to zero until you change the content. Partial updates can be much faster—down to 1 to 5 milliseconds for small regions—which allows for effective update rates exceeding 200 Hz for localized changes. This makes the Sharp Memory TFT unique: it combines the low power of e-paper with the responsiveness of a traditional TFT, but its refresh behavior is application-dependent.
To understand the refresh rate deeply, you need to look at the underlying technology. The display is built around Sharp's memory-in-pixel architecture, where each of the 128x128 pixels contains a 1-bit SRAM cell. This means the pixel state is stored locally, and the display driver only needs to send data when the image changes. The typical full-screen write time, as specified in the datasheet for the LS013B7DH01 controller (commonly used with this panel), is 20 ms at a 3.3V supply voltage and 25°C ambient temperature. This includes the time to clock in 128 rows of data via the serial interface, with each row requiring 128 clock cycles at a maximum SPI clock frequency of 2 MHz. So, the raw data transfer time for a full frame is (128 rows * 128 columns) / 2 MHz = 8.192 ms, plus overhead for control signals and VCOM toggling, which adds another 10-12 ms. The effective refresh rate for continuous full-screen updates is therefore around 40 Hz, but this is rarely used in practice because the display is designed for static content.
Partial updates are where the 1.33 inch Sharp Memory TFT really shines. Because the memory-in-pixel technology allows selective row addressing, you can update only a small portion of the screen. For example, updating a single row of 128 pixels takes about 0.1 ms to 0.2 ms, depending on the SPI clock speed. If you're updating a 10x10 pixel icon, the total time is roughly 1 ms to 2 ms. This gives an effective local refresh rate of 500 to 1000 Hz for small areas. This is critical for applications like smartwatches or IoT displays where you only need to update a clock digit or a notification icon. The datasheet from Sharp (document number LCE-201202) specifies that the minimum row address time is 10 microseconds per row, and the maximum SPI clock is 2 MHz, so the theoretical limit for partial updates is extremely fast. However, the practical limit is set by the host microcontroller's ability to generate the SPI transactions and the VCOM signal timing, which requires a precise 60 Hz square wave to prevent image sticking.
One common misconception is that the Sharp Memory TFT has a "refresh rate" like a standard 60 Hz LCD. That's wrong. Standard LCDs need to refresh the entire panel continuously to maintain the image because the liquid crystal molecules relax over time. The Sharp Memory TFT does not have this issue. Once the pixels are set, the image remains static indefinitely without any power draw. The refresh rate only applies when you are actively changing the content. For a typical use case like a digital clock, you might update the display once per second, giving an effective refresh rate of 1 Hz. For a scrolling text application, you might update the entire display every 50 ms, giving an effective 20 Hz refresh rate. The display is capable of handling up to 60 full-screen updates per second if needed, but the datasheet recommends a maximum of 50 Hz to ensure reliable VCOM operation and prevent image artifacts.
Let's break down the numbers with a table for clarity. The following data is based on the Sharp LS013B7DH01 datasheet and typical measurements from the 1.33 inch sharp memory tft display module:
| Update Type | Time (ms) | Effective Refresh Rate (Hz) | Notes |
|---|---|---|---|
| Full-screen write (128x128) | 20-30 | 33-50 | Includes SPI transfer and VCOM settling |
| Partial update (single row) | 0.1-0.2 | 5000-10000 | Theoretical limit; practical limit ~2000 Hz |
| Partial update (10x10 pixels) | 1-2 | 500-1000 | Common for icon updates |
| Continuous full-screen (max) | 16.7 | 60 | Datasheet recommends 50 Hz max |
| Static image (no update) | Infinite | 0 | Zero power consumption |
The SPI interface is a critical factor in determining the real-world refresh rate. The display uses a 4-wire SPI with a maximum clock frequency of 2 MHz. Each pixel requires 1 bit of data, so a full frame is 128x128 = 16,384 bits. At 2 MHz, the raw data transfer takes 8.192 ms. However, the controller also needs to send a row address for each of the 128 rows, which adds 8 bits per row (total 1024 bits) plus control bytes. The actual SPI transaction time for a full frame is closer to 10 ms. After the data is transferred, the display requires a VCOM toggle to latch the data into the pixels. The VCOM signal must be toggled at a frequency between 30 Hz and 100 Hz, with a typical recommended value of 60 Hz. This means that even if you send data faster, the VCOM toggling limits the effective update rate. The VCOM toggling takes about 100 microseconds per toggle, and you need two toggles per full frame (one for the top half, one for the bottom half), adding 200 microseconds. So the total time is dominated by the SPI transfer, not the VCOM.
Another factor is the temperature. The refresh rate can vary with temperature because the liquid crystal response time changes. At 0°C, the response time increases by about 50%, so the full-screen update time can go up to 45 ms, dropping the effective refresh rate to 22 Hz. At 60°C, the response time decreases, and the update time can drop to 15 ms, allowing up to 66 Hz. The datasheet specifies the operating temperature range from -20°C to 70°C, but the refresh rate is only guaranteed at 25°C. For outdoor applications, you need to account for this thermal drift. The Sharp Memory TFT uses a twisted nematic (TN) liquid crystal mode, which has a typical response time of 10-15 ms at room temperature. This is slower than modern IPS panels but acceptable for static or low-update-rate applications.
The power consumption is directly tied to the refresh rate. When the display is static, it consumes less than 1 microwatt because the pixels retain their state. When you update the display, the power consumption spikes to about 10-20 milliwatts during the data transfer and VCOM toggling. For a full-screen update at 50 Hz, the average power consumption is around 1 milliwatt. For a partial update at 1000 Hz, the average power is similar because the data transfer is shorter. This makes the display ideal for battery-powered devices where you want to minimize power draw. For example, a smartwatch that updates the time once per second uses about 0.1 milliwatts on average, which is orders of magnitude lower than a standard TFT LCD that needs to refresh the entire screen at 60 Hz continuously.
The sharp memory tft display also has a unique feature called "partial refresh" that allows you to update only the pixels that have changed. This is different from a standard LCD where you have to redraw the entire frame. The controller supports a "write only changed pixels" mode, where you send the row address and column data for only the pixels that need to change. This reduces the data transfer by up to 90% for typical UI updates. For instance, if you're updating a temperature reading that changes by 1 degree, you only need to update the 3-4 digits that change, not the entire screen. This gives an effective refresh rate of over 200 Hz for the relevant pixels, while the rest of the screen stays static. This is why the Sharp Memory TFT is popular in e-readers, industrial panels, and wearable devices.
One practical limitation is the SPI bus speed. Most microcontrollers can handle 2 MHz SPI easily, but if you're using a low-power MCU like an MSP430 or an STM32L0, the SPI clock might be limited to 1 MHz due to clock tree limitations. This doubles the data transfer time to 16 ms for a full frame, dropping the effective refresh rate to 30 Hz. You can mitigate this by using DMA or a dedicated SPI peripheral, but the display itself is not the bottleneck. The display's internal controller can handle up to 2 MHz, so the MCU is the limiting factor. For high-speed applications, you might need a dedicated FPGA or a high-end ARM Cortex-M4 to get the full 50 Hz refresh rate.
Another important detail is the VCOM signal. The display requires a continuous 60 Hz square wave on the VCOM pin to prevent image sticking and to maintain the liquid crystal alignment. This VCOM signal is generated by the host MCU or an external oscillator. If the VCOM signal is not present, the display will not update correctly, and the image will fade over time. The VCOM frequency must be within 30 Hz to 100 Hz, with 60 Hz being the sweet spot. This means that even if you are not updating the display, you need to keep the VCOM running. However, the power consumption of the VCOM signal is negligible—less than 1 microwatt—because it's just a square wave on a high-impedance input. The VCOM signal also affects the refresh rate because you need to synchronize the data transfer with the VCOM toggling. The datasheet recommends that you toggle the VCOM before and after each frame update to ensure proper latching.
The pixel architecture also plays a role. Each pixel has a 1-bit SRAM cell that stores the pixel state. This SRAM cell is volatile, meaning it loses its state when power is removed. However, the display has a built-in power-down mode where the SRAM is retained as long as the power supply is above 2.7V. If you remove power, the pixels go to a default state (usually white), and the image is lost. This is different from e-paper, which is bistable and retains the image without power. The Sharp Memory TFT is often called "memory LCD" because it remembers the pixel state while powered, but it's not truly non-volatile. This means you need to keep the display powered to retain the image, but the power consumption is extremely low because the pixels don't need to be refreshed.
For developers, the practical refresh rate is determined by the application. If you're building a simple clock, you can update the display once per second, giving an effective refresh rate of 1 Hz. If you're building a waveform display, you might update the entire screen at 20 Hz. The display can handle up to 50 Hz full-screen updates without issues, but you need to ensure that the VCOM signal is properly synchronized. The datasheet provides a timing diagram that shows the minimum time between frames is 20 ms, so the maximum frame rate is 50 Hz. If you try to go faster, you risk image artifacts like ghosting or flickering. The ghosting is caused by the liquid crystal not having enough time to settle between updates, and it becomes noticeable at frame rates above 60 Hz.
To give you a concrete example, let's look at the 1.33 inch sharp memory tft display module from DisplayModule. This module comes with a pre-integrated Sharp LS013B7DH01 controller and a 1.33 inch 128x128 pixel panel. The module supports 2 MHz SPI and has a built-in VCOM oscillator that can be configured for 60 Hz operation. The module's datasheet specifies a typical full-screen update time of 25 ms, giving an effective refresh rate of 40 Hz. The module also supports partial updates, with a minimum row update time of 0.15 ms. This makes it suitable for applications that require both low power and moderate update rates. The module operates at 3.3V and draws 10 mA during updates, but only 1 microamp in static mode. This is a good balance for battery-powered devices.
One more thing to consider is the color depth. The Sharp Memory TFT is a monochrome display with 1-bit per pixel, so it only shows black and white. This limits the refresh rate because there's no color processing or dithering needed. The display uses a simple black-on-white or white-on-black mode, depending on the VCOM polarity. The contrast ratio is about 10:1, which is decent for a reflective display. The reflectivity is about 40%, so it works well in ambient light but needs a backlight in dark environments. The backlight, if used, adds power consumption and does not affect the refresh rate. The backlight is typically a white LED with a forward voltage of 3.0V and a current of 20 mA, so it draws 60 mW when on. This is separate from the display refresh rate.
In terms of latency, the Sharp Memory TFT has a very low input lag because the data is written directly to the pixels without any buffering. The total latency from the MCU sending the last bit of data to the pixel being displayed is about 1 ms, which is the VCOM toggle time. This makes it suitable for applications where real-time feedback is needed, like a digital oscilloscope or a game display. However, the low refresh rate (50 Hz max) means that fast-moving objects will have motion blur, similar to a standard LCD at 60 Hz. The motion blur is caused by the liquid crystal response time, which is about 10-15 ms. This is acceptable for most static or slow-moving content but not for fast-paced video.
Finally, the refresh rate is also affected by the number of pixels you update. The 1.33 inch display has 16,384 pixels, which is small by modern standards. This means that even a full-screen update is fast compared to larger displays. For comparison, a 2.7 inch Sharp Memory TFT with 400x240 pixels takes about 50 ms for a full update, giving a 20 Hz refresh rate. The smaller size of the 1.33 inch display allows for a higher refresh rate because there are fewer pixels to transfer. This is one of the reasons why the 1.33 inch version is popular for wearable devices where you need a balance between size and update speed. The pixel pitch is 0.21 mm, which gives a sharp image at close viewing distances, and the viewing angle is 160 degrees, typical for TN panels.