Nec Electronics Corporation

Motoharu Kishi

Atsushi Iwata

Yoshitaka Murasaka

Toshifumi Imamura

Sadao Igarashi

Kouichi Kobinata

A photocoupler includes a LED for emitting light in accordance with an input electrical signal, a driver for supplying an electrical signal to the LED, a light receiver placed face to face with the LED and having a photodiode for receiving light emitted by the LED, and a half mirror placed between the LED and the photodiode, for changing the direction of light emitted by the LED. The photocoupler controls the current to be supplied to the LED in accordance with the reflected light by the half mirror to uniformize the light emission intensity of the LED.

Optical coupling device with a detecting element in the driver that provides uniform intensity of an optical signal

In an optical coupled isolation circuit, a PWM encoder encodes a one-bit binary data signal supplied from a sigma-delta analog-digital converter in synchronization with a clock signal of a cycle T to produce a pulse width modulation signal. The pulse width modulation signal includes a narrower pulse having a width of 1/T and a wider pulse having a width of 3/T according to binary codes '0' and '1'. The pulse width modulation signal is transmitted to a decoder as a recovered pulse width modulation signal through a light emitting device, a light detector and an optical recovery circuit. A decoder decodes the recovered pulse width modulation signal at timing of a half of the clock cycle from each rising edge of the recovered pulse width modulation signal. The rising edge is synchronized with the clock signal. Thus, the clock signal and the data signal can be transmitted in one channel.

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Kanagawa, Japan

Motoharu Kishi