Book Analog Interfacing to Embedded Microprocessors
convert the analog output into a digital level.
Optoisolators have the same speed and gain issues that optical sensors do.
The CTR of an optoisolator can be higher, typically in the 20% to 100% range,
because the LED is closer to the phototransistor base.
68 Analog Interfacing to Embedded Microprocessors
Figure 3.13
6N136.
The speed of an optoisolator is usually better than for an optical switch.
The common 4N35 optoisolator has turn-on and turn-off times of 10 ms each,
so it can pass signals over 10 Khz. However, as signals approach the limits of
the optoisolator speed, the output signal looks less like the input.
For high-speed isolation, a fast optoisolator is normally used. The 6N136
(Figure 3.13) is capable of speeds up to about 1 MHz. This part uses a photo-
diode coupled to a transistor to achieve high speed.
Discrete Optical Sensors
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