Method and circuit arrangement for measuring the light output of an emitter diode of an optical monitoring unit

An optical monitoring arrangement comprising a receiving unit and a transmitting unit, wherein:

• said transmitting unit comprises plural pairs of photodiodes, a current source, and a load resistor;
• said receiving unit comprises at least one receiving diode arranged separately from said plural pairs of photodiodes;
• said pairs of photodiodes of said transmitting unit each include two respective diodes that are arranged immediately adjacent to each other and that are connected to each other at a respective diode pair connection node;
• said current source is connected in series with a selected first one of said diodes of each one of said plural pairs of photodiodes, to a common reference voltage point;
• said load resistor is connected in series with a selected second one of said diodes of each one of said plural pairs of photodiodes, to said common reference voltage point;
• said current source is adapted to cause an activation current to flow through said first one of said diodes of at least a selected one of said pairs of photodiodes and thereby to cause said first one of said diodes to emit light, a first portion of which impinges on said second one of said diodes of said selected one of said pairs of photodiodes, and a second portion of which is emitted from said transmitting unit;
• said second one of said diodes of said selected one of said pairs of photodiodes is adapted to generate a, photoelectric current that flows through said load resistor responsive to said first portion of said light impinging on said second one of said diodes;
• and
• said receiving diode is adapted to receive an externally reflected portion of said second portion of said light that is reflected back to said receiving unit from an external environment outside of said optical monitoring arrangement.

A method of operating an optical monitoring arrangement including plural photodiodes in a transmitting unit and at least one receiving diode spatially separated from said plural photodiodes, said method comprising the steps:

• a) emitting light from a first one of said photodiodes, such that a first portion of said light impinges on a second one of said photodiodes and a second portion of said light is emitted from said transmitting unit into an external environment outside of said optical monitoring arrangement;
• b) receiving said first portion of said light with said second one of said photodiodes, and responsively thereto generating a photoelectric current or a photoelectric voltage in said second one of said photodiodes;
• c) evaluating said photoelectric current or said photoelectric voltage as being indicative of a light output of said light emitted from said first one of said photodiodes;
• d) receiving with said at least one receiving diode an externally reflected portion of said second portion of said light that is reflected from said external environment back to said at least one receiving diode, and responsively thereto generating a signal representative of a feature of said external environment;
• and
• e) selecting a first different one of said plural photodiodes as said first one of said photodiodes, selecting a second different one of said plural photodiodes as said second one of said photodiodes, and then repeating at least said steps a), b) and c) with said first and second different ones of said photodiodes.

A method of operating an optical transmitting unit including:

• a first photodiode;
• a second photodiode;
• an electrical power source;
• an electrical current or voltage measuring device;
• and
• a circuit arrangement adapted selectively to connect either selected one of said photodiodes to said electrical power source so that said selected one of said photodiodes operates as a transmitting diode and emits light, and simultaneously to connect the other one of said photodiodes to said measuring device so that said other one of said photodiodes operates as a monitoring diode and generates a photoelectric current responsive to receiving a portion of the light emitted by said selected one of said photodiodes, wherein said method comprises the steps:
• a) selecting said first photodiode as said selected one of said photodiodes, switching said circuit arrangement to connect said first photodiode to said power source and to connect said second photodiode to said measuring device, operating said first photodiode as said transmitting diode and emitting light therefrom, and operating said second photodiode as said monitoring diode and generating a photoelectric current therewith responsive to receiving a portion of said light emitted by said first photodiode;
• and
• b) at a time other than said step a), selecting said second photodiode as said selected one of said photodiodes, switching said circuit arrangement to connect said second photodiode to said power source and to connect said first photodiode to said measuring device, operating said second photodiode as said transmitting diode and emitting light therefrom, and operating said first photodiode as said monitoring diode and generating a photoelectric current therewith responsive to receiving a portion of said light emitted by said second photodiode.