Distance sensor
The present embodiment relates to a distance sensor that reduces a difference in amounts of current injected into each of plural charge collection regions prepared for one photosensitive region in order to avoid saturation caused by disturbance light. A current injection circuit injecting current into each charge collection region includes a voltage generation circuit generating a control voltage for adjustment of the injected current amount, and the voltage generation circuit generates the control voltage corresponding to a large amount of charge between the charge amounts of storage nodes coupled, respectively, to the charge collection regions. Meanwhile, a cascode device is disposed between a transistor configured to adjust the amount of current according to the control voltage and the storage node, and a potential of a current output end of the transistor and a potential of the storage node are separated.
1. A distance sensor configured to irradiate an object with light and measure a distance to the object by detecting reflected light from the object, the distance sensor comprising:
a semiconductor substrate having a photosensitive region generating charges corresponding to a light amount of the reflected light, and first and second charge collection regions each collecting the charges from the photosensitive region, the first and second charge collection regions disposed in the state of being separated from the photosensitive region by a predetermined distance;
a first transfer electrode disposed on a region between the photosensitive region and the first charge collection region, the first transfer electrode being set to an on-potential configured to enable charge transfer from the photosensitive region to the first charge collection region during a first period after irradiation of light, and set to an off-potential configured to stop the charge transfer during a second period following the first period;
a second transfer electrode disposed on a region between the photosensitive region and the second charge collection region, the second transfer electrode being set to an off-potential configured to stop charge transfer from the photosensitive region to the second charge collection region during the first period, and set to an on-potential configured to enable the charge transfer during the second period;
a voltage generation circuit having one end connected to a first constant potential line set to a predetermined potential and another end connected to a second constant potential line set to a lower potential than the first constant potential line, the voltage generation circuit being configured to generate a control voltage corresponding to a larger one between a charge amount stored in a storage node coupled to the first charge collection region and a charge amount stored in a storage node coupled to the second charge collection region;
first and second transistors each having a control terminal to which the control voltage is applied, a first current terminal connected to the first constant potential line, and a second current terminal;
a third transistor having a first current terminal connected to the second current terminal of the first transistor, a second current terminal connected to the storage node coupled to the first charge collection region, and a control terminal to be applied with a constant voltage; and
a fourth transistor having a first current terminal connected to the second current terminal of the second transistor, a second current terminal connected to the storage node coupled to the second charge collection region, and a control terminal to be applied with a constant voltage.
2. The distance sensor according to claim 1 , wherein
the third and fourth transistors are MOSFETs.