Photo Detectors – Logic Output

1. What are Logic Output Photo Detectors?

Logic output photo detectors are photo sensors with integrated signal processing capabilities that can directly convert received light signals into digital logic levels (such as TTL/CMOS-compatible signals). Their core advantage lies in their built-in comparator circuit, which enables light intensity threshold determination and outputs high/low signals without external signal processing.

 

2. What are the Operating Principles of Logic Output Photo Detectors?

Photoelectric Conversion Stage: The incident light signal is converted into a current signal using a PIN diode or APD (avalanche photodiode).

 

Signal Processing Stage: A built-in transimpedance amplifier (TIA) and Schmitt trigger amplify and shape the signal to eliminate noise interference.

 

Logic Output Stage: When the light intensity exceeds a preset threshold, a high level (such as 3.3V/5V) is output; otherwise, a low level (0V) is output, achieving a binary “light present/absent” determination.

 

3. What are the Technical Features of Logic Output Photo Detectors?

Fast Response: Typical rise/fall times can reach nanoseconds, making them suitable for high-speed optical communication systems.

 

Wide Dynamic Range: Adjustable threshold voltage to adapt to varying lighting conditions (e.g., 0.1mW/cm² to 100mW/cm²).

 

Low Power Design: Quiescent current is typically less than 1mA, making it suitable for battery-powered devices.

 

Anti-interference Capability: Built-in filtering circuitry suppresses the effects of ambient light fluctuations.

 

4. What are the Typical Application Scenarios of Logic Output Photo Detectors?

Industrial Automation: Object position detection, assembly line counting (e.g., encoder signal decoding).

Consumer Electronics: Smartphone proximity sensors, automatic brightness adjustment.

 

Optical Communications: Fiber link status monitoring (e.g., optical signal reception in ONU devices).

 

Security Systems: Infrared intrusion alarms, laser safety interlocks.

 

5. Key Selection Parameters of Logic Output Photo Detectors

Response Wavelength: Common wavelengths are 850nm/940nm/1550nm.

 

Output Type: Push-pull/open-drain.

 

Operating Voltage: 3.3V/5V/12V, etc.

 

Packaging: TO-46/SMD/COB.

 

6. Examples of Mainstream Logic Output Photo Detectors

LTR-390: A low-cost, general-purpose model suitable for consumer electronics.

 

SFH-340: High-speed industrial grade (5ns response time).

 

TSOP-4836: Dedicated for infrared remote control receivers.