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LF-ANTENNA

DOOR type LF antenna

Door-type antennas are located inside or near the vehicle exterior door handle and send out LF triggers in the event of a door access event. Most are located inside the door handle and are interlocked with proximity sensors or door touch sensors.

● SYSTEM FLOW

Access detection

In system standby, sensors near door detect access
(capacitance, IR probability, etc.)

LF transmit

Door-type LF antennas transmit signals at approximately 125 kHz

FOB response

Smart key (FOB) sends corresponding UHF response after LF reception
(315/433MHz or 868/915MHz)

Certification

Vehicle ECU performs key authentication and distance determination
door unlock or lock
● feature
  • Signal coverage is limitedly designed(for the purpose of preventing bumpers or internal interference)
  • Multiple LF antennas (four doors, trunk, console, etc.)to secure communication redundancy
  • H-field based distance estimationis possible (based on actual signal strength)
● SPEC.
Installation Location Inside the door handle LH/RH Front Door
Signal coverage Up to 0.7 to 1.2 m, spherical distribution Oval diffusion, based on -6db coverage
magnetic field strength @300mm Based on distance ≥ 2.0 A/ms (based on ISO 14223, etc.)
Resonant circuit design LC parallel resonance circuit C = tens of nF/L = several mH
Voltage supply (Vcc) Mainly 5V (some 3.3V) 5V ±10%
Average consumption current Average based on Tx Pulse 5-20 mA (based on bust)
Antenna inductance High inductance design 2~8 mH
EMI Shielding Necessity Shield can + PCB GND Plane

SWITCH type LF antenna

The switched LF antenna is a trigger antenna that is activated by user input by interlocking with a physical button built into the door handle or a touch input unit. The LF signal is only sent when explicitly entered by the user.

● SYSTEM FLOW

Switch Button

The driver presses the switch/press on the door handle

ECU Receipt

ECU receives the event → LF antenna transmission trigger

Smart Key Communication

Smart Key LF Received → Send UHF Response

ECU key authentication

ECU key authentication → door control
● feature
  • Generally, Low cost and Structure Simple
  • Simplify wiring as it works with external switches, not inside the door
  • Enable system EMI stability by suppressing unnecessary LF transmission
● SPEC.
Installation Location Door handle outer button or near touch panel Rear door, trunk
signal range Limited, recommended within tens of cm 0.3~0.6 m
Trigger Method GPIO/Interrupt + Software Control Switch Input → Tx Pulse
voltage supply (Vcc) 5V or 3.3V 3.3V Easy to match with the system
current consumption Only short transmission works 1~5 mA (pulse Time is very short)
Resonant characteristics Narrow bandwidth, low Q design Q ≈ 20~50
Durability Requirements Interworking with button click lifetime 100,000 or more times (on a button-in-one basis)
EMC Requirements Low Burst EMI limit low