초록 ▼

In a common package, a light emitter, which is responsive to an input signal, produces an output optical signal which is coupled through an optically transmissive electrical insulator to a principal photodetector disposed in stray capacitive coupled relation to the light emitter for detecting the op

In a common package, a light emitter, which is responsive to an input signal, produces an output optical signal which is coupled through an optically transmissive electrical insulator to a principal photodetector disposed in stray capacitive coupled relation to the light emitter for detecting the optical signal to produce an output signal in response thereto. A dummy photodetector, which has similar electrical characteristics to that of the principal photodetector except that it is rendered nonresponsive to the output optical signal is similarly coupled in stray capacitive relation to the light emitter to derive a dummy output signal. The dummy signal together with the principal output signal are fed to the differential input terminals of a differential amplifier which takes the difference of the two signals, thereby cancelling common mode signal components capacitively coupled to said photodetector and producing an amplified output signal.

대표청구항 ▼

The method for increasing the common mode rejection between the input and output of an optically coupled isolator circuit of the type wherein, in a common package, a light emitter means which is responsive to an input signal produces an output optical signal which is coupled through an optically tra

The method for increasing the common mode rejection between the input and output of an optically coupled isolator circuit of the type wherein, in a common package, a light emitter means which is responsive to an input signal produces an output optical signal which is coupled through an optically transmissive electrical insulator to a principal photodetector disposed in stray capacitive coupled relation to said light emitter means for detecting the optical signal to produce an output signal in response thereto, the steps of: coupling a dummy photodetector, which has similar electrical characteristics to said principal photodetector means except being nonresponsive to the output optical signal, in stray capacitive coupled relation to said light emitter means, such stray capacitive coupling being similar in phase and magnitude to the stray capacitive coupling between said principal photodetector and said light emitter, to derive a dummy output electrical signal from said dummy photodetector which is nearly the same as that derived from said first photodetector except for the detected optical signal component in the output of said principal photodetector; and taking the difference between said dummy output signal and said output signal from said principal photodetector to derive a difference signal output having increased common mode rejection.