EMR is the abbreviation of Electro Magnetic Resonance technology. Touch displays adopting this technology are commonly referred to as electromagnetic digitizer displays.
Electromagnetic pens can be classified into active pens (with an internal battery, generally considered lower-end) and passive pens (without an internal battery, powered by the electromagnetic field generated by the digitizer).
WACOM is the absolute leader and de facto monopolist in passive EMR pen technology.
1. EMR System Components
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Electromagnetic pen
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Cover glass
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LCD panel
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Digitizer (electromagnetic sensing board)
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Shielding plate
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Digitizer Control Board (DCB)
The components located around the digitizer that generate and receive electromagnetic fields through high-speed switching are collectively referred to as the digitizer module.
Wacom’s pen input system consists of:
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The digitizer (also called Antenna Grid Board)
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The electromagnetic pen
The digitizer module itself is composed of:
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The digitizer (antenna grid board)
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The Digitizer Control Board (DCB)
2. Basic Principle of EMR
The electromagnetic pen emits an electromagnetic signal and interacts with the digitizer located behind the display panel.
When the pen approaches the screen, the digitizer senses the electromagnetic signal emitted by the pen, causing changes in the sensing coils beneath the digitizer. By receiving signals through antenna arrays arranged in both horizontal and vertical directions, the system calculates the magnetic flux variation to determine the pen’s X and Y coordinates.
3. Pen Position Detection
Pen positioning is achieved through orthogonally arranged coils in the X and Y directions.
4. EMR Operating Sequence
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The digitizer coils are energized to generate a magnetic field
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The pen is powered (inductive energy transfer)
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The coils are de-energized and switch to receive mode
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The pen performs frequency modulation and resonance, feeding signals back to the digitizer
5. Pressure Sensitivity Implementation
The pen tip is mounted in front of flexible silicone rubber and conductive rubber.
During writing, the pen tip pushes the conductive rubber backward and forward, changing the distance between it and the capacitive electrodes. By detecting changes in capacitance, pressure sensitivity can be achieved.
This method supports up to 4,096 pressure levels, and current implementations support 8,192 levels.
6. Digitizer Control Board (DCB)
COB (Chip-on-Board) Design
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Increased pin count, up to 100 pins
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Maximum thickness: 0.32 mm
Module Design
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The DCB is bonded directly to the digitizer grid board
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Connected using ACF (Anisotropic Conductive Film)
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Pin count can be reduced to 8 pins
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Maximum thickness: 1.2 mm
7. Digitizer Outline Design Rules
A (mm): Distance from Digitizer Active Area to Digitizer Outline (X and Y axes)
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A = 3.5 mm for LCD ≤ 15 inches
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A = 6.0 mm for LCD > 15 inches
e (mm): Distance from LCD Active Area to Digitizer Active Area
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1.0 mm for general cases
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0 mm to comply with Windows 10 logo certification requirements
The LCD Active Area (LCM-AA) and Digitizer Active Area (Digitizer-AA) must be aligned at the center point (CP).
Normal Border Width
Adequate border width ensures proper signal detection.
Insufficient Border Width (Signal Loss)
If the border width is narrower than the required 4.5 mm / 7 mm, the digitizer layout, which requires at least 3.5 mm / 6 mm, will overlap with the non-effective border region, resulting in signal loss in those areas.
8. Structural Configurations
Connected Structure
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The opening area of the rear light-shielding plate must be equal to or larger than the digitizer active area
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The rear shielding plate must not use magnetic materials such as iron, cobalt, or nickel
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The combined distance between the rear shielding plate and the DSA must be less than 0.3 mm
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If masking tape or conductive tape is used for LCM grounding, materials containing iron, cobalt, or nickel must also be avoided
Embedded Structure
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No requirement for an opening area in the rear shielding plate
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The rear shielding plate must not use magnetic materials such as iron, cobalt, or nickel
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If masking tape is used, materials containing iron, cobalt, or nickel must also be avoided
9. Electromagnetic Interference
Metal components on the digitizer can affect the EM signal of the pen.
Common interference mechanisms include:
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Magnetic field distortion
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Mitigation: Use SUS304 stainless steel
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Eddy current effects
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Mitigation: Use high-resistivity materials
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Sources of electromagnetic interference include:
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Rectifier circuits
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DC-DC converters
10. Introduction to Magnetic Shielding
Magnetic flux lines can only be constrained or guided, but cannot be cut.
Since free magnetic charges do not exist, a shielding enclosure cannot interrupt magnetic flux lines nor eliminate a magnetic field.
However, magnetic shielding can be used to redirect magnetic flux lines to avoid unwanted electromagnetic coupling.
This can be achieved by using high magnetic permeability materials, such as:
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SUS430 stainless steel
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Low-carbon steel
These materials alter the path of magnetic flux lines, thereby improving electromagnetic compatibility within the EMR system.
