The refresh rate of a Liquid Crystal Display (LCD) is a critical specification that reflects the number of times the display updates its image per second, typically measured in hertz (Hz). It plays a vital role in determining motion smoothness, response to fast-moving visuals, and synchronization with input signals. Understanding how refresh rate interacts with driving circuits, frame memory, and liquid crystal response characteristics is essential for optimizing both performance and power efficiency.
Let’s explores:
- Real example calculation comparing 16-bit vs 24-bit RGB for a 7.0″ 1024×600 TFT panel
- Key Parameters That Affect LCD Refresh Rate
- How it continues to evolve with display technology.
Refresh rate means how many times per second the LCD updates the image on the screen.
It is measured in hertz (Hz) — for example:
- 60 Hz → the display refreshes 60 times per second
- 120 Hz → 120 times per second
Even though the image may not always visibly change, the panel still refreshes its pixels at that rate. A higher refresh rate usually gives smoother motion and less flicker.
Key Parameters That Affect LCD Refresh Rate
- Interface Bandwidth / Pixel Clock (DCLK or DOTCLK)
- This is the most important factor.
- The pixel clock defines how fast pixel data are transmitted from the driver (MCU, GPU, or controller) to the LCD module.
- Formula (approx.):
Where
Example:
let’s go step by step with a 7.0″ TFT display (1024 × 600 resolution) and compare 16-bit RGB vs 24-bit RGB interface.
Step A. Basic Display Parameters
| Item | Symbol | Typical Value |
| Active pixels (horizontal) | H_active | 1024 |
| Active pixels (vertical) | V_active | 600 |
| Horizontal blanking (porch + sync) | H_blank | 32 |
| Vertical blanking (porch + sync) | V_blank | 23 |
| Total horizontal pixels | H_total | 1024 + 32 = 1056 |
| Total vertical pixels | V_total | 600 + 23 = 623 |
So total pixels per frame:
A 1024×600 TFT with a 40 MHz pixel clock →
Step B. Set Target Refresh Rate (e.g., 60 Hz)
We want:
Then pixel clock must be:
Conclusion: Roughly a 40 MHz dot clock is needed for 60 Hz refresh.
Step C. Calculate Data Bandwidth
Case A: 16-bit RGB (RGB565)
Each pixel = 16 bits = 2 bytes
≈ 79 MB/s
Case B: 24-bit RGB (RGB888)
Each pixel = 24 bits = 3 bytes
≈ 118 MB/s
Step D. Compare
| Parameter | 16-bit RGB | 24-bit RGB | Difference |
| Bits per pixel | 16 | 24 | +50% |
| Bandwidth needed | 632 Mbps | 948 Mbps | +50% |
| *Refresh rate (if pixel clock fixed at 40 MHz) | 60 Hz | ~40 Hz | ↓ 33% |
| Color quality | 65 K colors | 16.7 M colors | ↑ massively |
*At any fixed interface bandwidth, 24-bit needs 50% more bandwidth than 16-bit, so its achievable refresh rate is 2/3 of 16-bit’s (if everything else is equal).
Step E. Critical Thinking:
- The refresh rate is limited by the pixel clock (DCLK).
- If your LCD controller has a fixed bandwidth, using 24-bit RGB means you must lower the refresh rate or use a faster clock / better interface (e.g. LVDS, MIPI-DSI).
- For small embedded systems, 16-bit RGB is often chosen because it maintains 60 Hz refresh without needing a high-speed interface.
- Resolution (number of pixels)
- Higher resolution = more pixels to refresh → requires a higher pixel clock to keep the same frame rate.
- For example, 800×480 needs less bandwidth than 1920×1080 for the same refresh rate.
- Color Depth (Bits per Pixel)
- 24-bit RGB (8 bits per color) transfers 50% more data than 16-bit RGB, so it may limit maximum refresh rate if bandwidth is fixed.
- Interface Type
- Parallel RGB (DOTCLK) — refresh rate directly tied to pixel clock.
- LVDS, eDP, MIPI-DSI — higher data rate interfaces that allow higher refresh rates.
- SPI/MCU Interface — limited bandwidth, usually for lower resolution displays.
- Panel Response Time
- Response time is how fast the liquid crystal changes state (in milliseconds).
- Even if the refresh rate is high, slow response time can cause motion blur.
| Parameter | Impact on Refresh Rate | Notes |
| Pixel Clock (DCLK) | Directly determines refresh rate | Higher clock = faster refresh |
| Resolution | Inversely proportional | More pixels = lower refresh if clock fixed |
| Color Depth | Affects data throughput | Higher bit depth = slower if bandwidth limited |
| Interface Type | Sets max possible rate | SPI ≪ RGB ≪ LVDS/MIPI |
| Response Time | Doesn’t change refresh rate but affects motion clarity | Measured in ms |
The relationship between refresh rate and refresh time is inversely proportional. As the refresh rate increases, the duration of each frame period decreases, allowing images to be updated more frequently. Table 1 below illustrates this relationship for several common refresh rate values used in LCD panels.
Table 1. Relationship Between Refresh Rate and Frame Refresh Time
| Refresh Rate (Hz) | Frame Time (milliseconds) | Explanation |
| 30 Hz | 33.33 ms | Each image is displayed for one-thirtieth of a second; suitable for static or low-motion displays. |
| 60 Hz | 16.67 ms | Standard rate for most consumer LCDs; offers good balance between smoothness and power efficiency. |
| 90 Hz | 11.11 ms | Provides noticeably smoother motion; used in high-end smartphones and VR headsets. |
| 120 Hz | 8.33 ms | Common for gaming and automotive displays requiring fast motion response. |
| 240 Hz | 4.17 ms | Enables extremely fluid motion; mainly used in professional gaming monitors and advanced prototypes. |
From a performance standpoint, higher refresh rates improve motion fluidity and reduce flicker, resulting in a more stable and comfortable viewing experience. Applications such as gaming, augmented reality, and high-speed instrumentation often benefit from 120 Hz or higher operation. Conversely, static or semi-static displays operate efficiently at lower frequencies, balancing performance with energy savings. Adaptive and variable refresh rate technologies now dynamically adjust the frequency according to displayed content, achieving both visual stability and power optimization.
In summary, the refresh rate embodies a complex interaction between optical materials, electronic architecture, and perceptual quality. Through precise control of refresh timing and signal management, LCD technology continues to evolve toward faster, more power efficient, and more adaptive display performance.
Should you have any questions about LCD’s refresh rate, please consult our engineering.