Light receiving circuit
View Patent ↗Provided is a light receiving circuit including: a photodiode; a first amplifier including a feedback resistor connected between an input and an output of an inverting amplifier and having an input connected to a cathode of the photodiode; a second amplifier having a configuration similar to that of the first amplifier and having an input connected to an anode of the photodiode; a capacitor element connected between an output of the first amplifier and the input of the second amplifier; and a bias current control circuit that outputs a bias current to the input of the second amplifier according to a current value of the photocurrent, and controls an output voltage signal of the light receiving circuit according to an output of the second amplifier by using the bias current to adjust the sensitivity. The bias current control circuit changes the sensitivity according to the output of the second amplifier.
1. A light receiving circuit comprising:
a photodiode that outputs a photocurrent in response to a received light signal;
a first amplifier including a feedback resistor connected between an input terminal and an output terminal of an inverting amplifier, and having an input terminal connected to a cathode of the photodiode;
a second amplifier having a configuration similar to that of the first amplifier, and having an input terminal connected to an anode of the photodiode;
a capacitor element connected between an output terminal of the first amplifier and the input terminal of the second amplifier; and
a bias current control circuit that outputs a bias current to the input terminal of the second amplifier according to a current value of the photocurrent, and controls an output voltage signal according to an output of the second amplifier by using the bias current to adjust sensitivity of the light receiving circuit,
wherein the bias current control circuit changes the sensitivity according to the output of the second amplifier.
2. The light receiving circuit according to claim 1 , wherein
the bias current control circuit comprises a third amplifier having a configuration similar to that of the first amplifier, and
the third amplifier outputs the bias current according to the current value of the photocurrent.
3. The light receiving circuit according to claim 2 , further comprising a fourth amplifier that has a configuration similar to that of the first amplifier and outputs a signal according to the output of the second amplifier,
wherein a control terminal of an output transistor of the third amplifier and a control terminal of an output transistor of the fourth amplifier are connected to each other.
4. The light receiving circuit according to claim 1 , wherein
the first amplifier comprises a first transistor serving as an input transistor, a second transistor serving as an output transistor, and first to third resistors,
the first resistor has one terminal connected to a first power supply voltage terminal, and another terminal connected to a first node,
the first transistor has one terminal connected to the first node, another terminal connected to a second power supply voltage terminal, and a control terminal connected to the input terminal of the first amplifier,
the second transistor has one terminal connected to the first power supply voltage terminal, another terminal connected to the output terminal of the first amplifier, and a control terminal connected to the first node,
the second resistor has one terminal connected to the output terminal of the first amplifier, and another terminal connected to the second power supply voltage terminal, and
the third resistor has one terminal connected to the input terminal of the first amplifier, and another terminal connected to the output terminal of the first amplifier.
5. The light receiving circuit according to claim 1 , wherein the light receiving circuit is used on a reception side of the photocoupler.