On-chip light sensor
AssigneeTexas Instruments Incorporated
InventorClaude E. Tew
Life of this patent
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Abstract
A brightness sensing circuit for providing a binary electrical signal for indicating whether incident light exceeds a certain brightness. The circuit's light detector is a photodiode, whose output is amplified by a first current mirror. The circuit has a reference current source, whose output is amplified by a second current mirror. Both currents are delivered to a common node, whose voltage level transitions from low to high when the amplified input current exceeds the amplified reference current. This node is connected to the gate input of a CMOS inverter, which provides a binary output.
Claims20
A circuit for providing an electrical signal to indicate when incident light exceeds or falls below a certain level of brightness, comprising:
- a photodiode for detecting incident light and generating an input current;
- a first current mirror for receiving and amplifying said input current and delivering the amplified input current to an intermediate node;
- a current source for providing a reference current;
- a second current mirror for receiving and amplifying said reference current and for delivering the amplified reference current to said intermediate node;
- and
- an inverter for receiving the current from said intermediate node and for changing state at its output when said amplified input current exceeds said amplified reference current.
A monolithic device which includes a deformable mirror and a circuit for indicating the brightness level of light incident on the mirror, comprising:
- at least one micro-mechanical mirror element on said device;
- and
- a shut-off circuit on said monolithic device comprising a photodiode for receiving a portion of said light incident on said monolithic device and providing an input current, a first current mirror for amplifying said input current to an intermediate node, a current source for providing a reference current, a second current mirror for amplifying said reference current to said intermediate node, and an inverter connected to said intermediate node for providing a binary output depending on the voltage at said intermediate node.
A method of measuring incident light comprising;
- generating an input current based on the level of said incident light;
- amplifying said input current;
- providing a reference current;
- outputting a first signal level when the magnitude of said amplified input current exceeds the magnitude of said reference current;
- and
- outputting a second signal level when the magnitude of said reference current exceeds the magnitude of said amplified input current.
Dependencies are inferred from the claim text.