Infrared receiver

The infrared receiver is the TV's eye for the remote control. It sits behind a small dark window on the front of the set, watching for flashes of infrared light that our eyes can't see, and turns them into a clean digital signal for the main board.

Inside is a silicon die carrying a light sensor, a photodiode that makes a tiny current when infrared hits it, plus an amplifier and filter circuit. In some designs the sensor and circuit share one chip; in others they are two chips side by side. The die is glued to a lead frame, whose three legs carry power, ground and the output signal, and joined to it by fine bond wires. It is then cast in epoxy resin dyed so dark it looks black. The dye blocks visible light, which would only add noise, but lets infrared through, and the epoxy is shaped into a small dome that acts as a lens.

The remote doesn't just switch its light on and off. During each pulse it flickers about 38,000 times a second, and the receiver listens only for that rate, ignoring sunlight and lamps, so the remote control's codes come through clearly.