What is CKV1, CKV2, CKVB, CKVB2 And Common Electrode of LCD?

CKV: In the intricate world of LCD (Liquid Crystal Display) technology, terms like CKV1, CKV2, CKVB, and CKVB2 often surface when discussing panel operation and repair. These signals are fundamental to how an LCD panel generates and controls the images we see. To truly grasp their function, one must first understand the underlying architecture of an LCD panel, particularly the role of the "Common Electrode."
At its core, an LCD screen displays images using millions of tiny dots, known as pixels. Each pixel is composed of three subpixels, each with a red, green, and blue color filter. Beneath each of these subpixels lies a tiny liquid crystal cell. These cells act as light shutters; by twisting or untwisting the liquid crystals inside them, they control how much backlight passes through the color filters, ultimately creating the vast spectrum of colors on the screen.
For each liquid crystal cell to function, it requires two electrical connecting points or electrodes. A voltage difference applied across these electrodes creates an electric field, which in turn determines the alignment of the liquid crystals. One of these electrodes is individual to each subpixel, while the other is a shared layer known as the "Common Electrode," which is where signals like CKV come into play.
What is the Common Electrode (Anode) in an LCD Panel?
As illustrated in the figure below, the anode electrodes of multiple liquid crystal cells are connected to a single, large conductive layer. This shared layer is known as the LCD's Common Electrode (also referred to as VCOM or Common Anode in some contexts). It serves as a universal reference point for electrical potentials across the entire display panel.
Figure 1: Simplified diagram illustrating the CKV connection to the Common Electrode in an LCD structure.
What is the Common Electrode (Anode) in an LCD Panel?
As illustrated in the figure above, the anode electrodes of multiple liquid crystal cells are connected to a single, large conductive layer. This shared layer is known as the LCD's Common Electrode (also referred to as VCOM or Common Anode in some contexts). It serves as a universal reference point for electrical potentials across the entire display panel.
The Common Electrode is crucial for controlling the alignment of liquid crystals, which dictates the passage of light to create images. Here’s a breakdown of its key functions:
1. Shared Reference Point: It acts as a common ground or reference voltage layer for nearly all pixels on the LCD panel. The state of each pixel is determined by the voltage difference between its individual pixel electrode and this common electrode.
2. Alignment of Liquid Crystals: By establishing a potential difference, the common electrode, in conjunction with the pixel electrode, creates the necessary electric field to orient the liquid crystal molecules. This orientation determines whether light is blocked or allowed to pass through.
3. Receives CKV Signals: Crucially, clock signals like CKV (Clocking Vertical) are applied to or influence the voltage of this common electrode layer to synchronize the row-by-row scanning process of the display.
4. Physical Placement: The common electrode is typically a transparent conductive layer (often made of Indium Tin Oxide - ITO) located on one of the glass substrates, sandwiching the liquid crystal layer between it and the individual pixel electrodes on the other substrate.
Overall, the common electrode is an indispensable component in LCD technology, enabling precise and synchronized control of liquid crystals for high-quality image production.
What are CKV1, CKV2, CKVB1, CKVB2 in LCD?
In the context of LCD panels, CKV stands for Clocking Vertical. These are essential clock signals used in the gate driver circuitry (often embedded on the glass, known as GOA - Gate on Array) to control the vertical scanning of the display. They ensure that each row of pixels is turned on and off at the precise moment required to build the image frame by frame.
The multiple CKV lines, such as CKV1, CKV2, and their inverted counterparts CKVB1, CKVB2 (where 'B' stands for Bar or inverted), are used to manage the timing and polarity of the gate pulses. This multi-phase clocking technique helps in:
• Reducing power consumption.
• Improving the charging characteristics of the pixels.
• Mitigating issues like image flickering and cross-talk.
These signals effectively modulate the voltage on the gate lines and indirectly influence the potential relative to the common electrode, facilitating the proper switching of the Thin-Film Transistors (TFTs) for each pixel row.
Figure 2: Typical test points for CKV1, CKV2, CKVB1, and CKVB2 on an LCD panel's T-con board or source PCB.
Where are the CKV lines connected in the LCD panel?
The CKV lines originate from the Power Management IC (PMIC) or a dedicated level shifter IC on the T-con (Timing Controller) board. From there, they are routed through the flexible flat cables (FFC) to the source PCB (the long board attached to the panel glass). Finally, they enter the glass panel itself to drive the Gate Driver circuitry, which is often integrated directly onto the glass substrate (GOA technology).

Inside the glass, these signals are ultimately functionally linked to the Common Electrode structure to manage the gate switching potentials. The number of CKV lines (e.g., CKV1, CKV2, CKV3, or CKV1, CKVB1, CKV2, CKVB2) depends on the specific design and resolution of the LCD panel.
How to find CKV lines on an LCD panel?
Identifying CKV lines is a critical step in diagnosing panel faults. You can find them using the following methods:
• Datasheet or Schematic: The most reliable method is to consult the datasheet or circuit diagram of the LCD panel or its PMIC/Level Shifter IC. For instance, for a Samsung LSC320AN10-XXX panel, you would check the schematic of its PMIC, such as the SM4168 IC. The pinout will clearly label the CKV outputs.
• PCB Test Points: Most T-con boards or source PCBs have labeled test points (like in Figure 2) for critical signals. Look for markings like CKV1, CKV2, CKVB1, CKVB2, STVP, etc., near the PMIC or the panel connector.
• Voltage Measurement: With the panel powered on, you can use an oscilloscope (recommended) or a multimeter to measure the signals at suspect test points. CKV signals are high-frequency pulsating DC voltages that swing between a high (VGH) and low (VGL) level.
For a deeper understanding of other critical panel voltages like AVDD, STV, VGH, VGL, and VCOM, you can read our detailed guide here: What are AVDD, STV, VGH, VCOM, VGL, and CKV?
CKV Short Killing Method: A Repair Technique
A common failure mode in LCD panels is a short circuit developing within the CKV lines inside the glass, often between a CKV line and another trace or the common electrode. This usually affects either the odd or even rows, leading to distorted images, horizontal lines, or a completely blank screen with the backlight on.
The "CKV Short Killing" method involves isolating the shorted CKV lines. This can sometimes be done by carefully cutting the problematic CKV tracks on the source PCB before they enter the glass. If successful, a part of the internal gate driver circuitry is disabled, but the remaining part may still be able to drive the panel, restoring the image (though sometimes with slightly reduced quality).
In cases where cutting tracks is not feasible or effective, technicians may use a specialized device known as a CKV Short Killer. This tool applies a controlled high-voltage pulse to the shorted line in an attempt to burn out the internal microscopic short circuit, thereby restoring normal operation.
Interested in building your own tool? Learn How to make a CKV Short Killer in our step-by-step tutorial.
For a practical demonstration of this repair technique, watch the video below:
Video: How to remove a CKV short on an LCD panel