Optical sensor, and electronic apparatus
A light receiving sensor ( 1 ) includes: a photodiode (PD) which generates a photocurrent (Ipd) upon receipt of light; a transistor (Tr 11 ) through which the photocurrent (Ipd) flows; a transistor (Tr 12 ) which forms, together with the transistor (Tr 11 ), a first current mirror circuit (CM 1 ); a transistor (Tr 9 ) whose channel type is different from that of the transistor (Tr 11 ), and a resistor (R 10 ) which converts, to a voltage, a current flowing through the transistors (Tr 11 and Tr 12 ). The first current mirror circuit (CM 1 ) amplifies the photocurrent (Ipd), the transistor (Tr 11 ) has a source connected with a gate of a MOS transistor (Tr 9 ), and the MOS transistor (Tr 9 ) has a threshold voltage that is set to be equal to or above a threshold voltage of the transistor (Tr 11 ). This decreases a capacity of the photodiode (PD) and therefore allows the light receiving sensor ( 1 ) to operate at a high speed while the photodiode (PD) is biased.
1. An optical sensor comprising:
a photodiode which generates a photocurrent upon receipt of light;
a first MOS transistor through which the photocurrent flows;
a second MOS transistor which forms, together with the first MOS transistor, a current mirror circuit;
a third MOS transistor whose channel type is different from that of the first MOS transistor; and
a current-voltage conversion element which converts, to a voltage, a current flowing through the second MOS transistor,
the current mirror circuit amplifying the photocurrent,
the first MOS transistor having a source connected with a gate of the third MOS transistor, and
the third MOS transistor having a threshold voltage that is set to be equal to or above a threshold voltage of the first MOS transistor.
2. The optical sensor according to claim 1 , wherein a back gate of the first MOS transistor is connected with a gate of the first MOS transistor.
3. The optical sensor according to claim 1 , further comprising:
an inverter which turns on or off the third MOS transistor by switching on or off in accordance with a voltage into which the photocurrent amplified by the current mirror circuit is converted,
wherein the inverter is formed by two inverter MOS transistors, one of which has a channel type that is identical to that of the first MOS transistor and has a back gate and a gate connected with each other.
4. The optical sensor according to claim 3 , wherein
the inverter MOS transistors are P-type MOS transistors, and
the optical sensor further includes a diode-connected N-type MOS transistor which is an auxiliary MOS transistor connected in series with the inverter MOS transistor.
5. The optical sensor according to claim 1 , wherein
the first MOS transistor is a P-type MOS transistor, and
both a drain and a gate of the first MOS transistor are connected with a cathode of the photodiode.
6. The optical sensor according to claim 1 , wherein
the first MOS transistor is an N-type MOS transistor, and
both a drain and a gate of the first MOS transistor are connected with an anode of the photodiode.
7. An electronic device comprising an optical sensor of claim 1 .