# US 9,753,060 B2 · Apparatus with device with fault detection protection > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,753,060 B2 - Document ID: US9753060B2 - Status: Granted - Kind: B2 - Application number: 14/838,447 - Filed: 2015-08-28 - Published: 2017-03-02 - Granted: 2017-09-05 - Earliest claimed: 2015-08-28 - Assignees: STMicroelectronics (Research & Development) Limited - Applicants: Stmicroelectronics (Research & Development) Limited - Inventors: Shatabda Saha - Web page: https://patentgrep.com/patent/US9753060B2 ## CPC - G01R 17/02: Arrangements in which the value to be measured is automatically compared with a reference value - G01C 3/02: Details - G01S 7/484: Transmitters - G01S 7/497: Means for monitoring or calibrating - G01S 17/10: using transmission of interrupted, pulse-modulated waves (determination of distance by phase measurements G01S17/32) - H01S 5/06825: {Protecting the laser, e.g. during switch-on/off, detection of malfunctioning or degradation} - G01R 19/16571: {comparing AC or DC current with one threshold, e.g. load current, over-current, surge current or fault current (G01R19/16514, G01R19/16519, G01R19/16528, G01R19/16533, G01R19/1659 take precedence; measuring currents by using elements sensitive to the magnetic field generated G01R15/14; measuring earth resistance G01R27/18; testing for leakage or short circuits in electrical apparatus G01R31/52)} - G01R 31/44: Testing lamps - H01S 5/0428: {for applying pulses to the laser} - H01S 5/183: having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S) - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES - H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL ## Abstract A device such as a laser diode is provided with a monitoring arrangement. The monitoring arrangement has voltage to current converters arranged to provide respectively currents which are proportional to the respective voltages on an anode and on a cathode of the laser diode. The monitoring arrangement provides a first output signal when the laser diode is on too long. That output signal is used to cause the laser diode to be switched off. ## Claims ### Claim 1 An apparatus comprising: a device configured to emit a photon and to be switched on and off by a driver circuit; a first voltage-to-current circuit configured to provide a first current dependent on a voltage at a first node of the device; a second voltage-to-current circuit configured to provide a second current dependent on a voltage at a second node of the device; a comparator configured to be responsive to the first current and the second current and to generate a first output when the device is switched on; and a monitoring circuit having an input coupled to an output of the comparator, the monitoring circuit being configured to receive the first output and to generate a control signal in response to the first output being received for greater than a threshold period of time, the control signal being configured to cause the driver circuit to switch off the device. ### Claim 2 (depends on 1) The apparatus according to claim 1, wherein the comparator is further configured to provide a different output when the device is switched off. ### Claim 3 (depends on 1) The apparatus according to claim 1, wherein said comparator comprises a first transistor configured to be responsive to said first current, a second transistor configured to be responsive to said second current and a node between said first and second transistors configured to provide said first output. ### Claim 4 (depends on 3) The apparatus according to claim 3, wherein said first and second transistors of said comparator are configured as current sources. ### Claim 5 (depends on 3) The apparatus according to claim 3, wherein said voltage-to-current circuits each comprise a transistor arranged in a mirrored arrangement with a respective one of said first and second transistors such that the respective first and second currents are upwardly scaled. ### Claim 6 (depends on 1) The apparatus according to claim 1, wherein the second current is substantially the same when the device is on and when said device is off. ### Claim 7 (depends on 1) The apparatus according to claim 1, wherein the first current is substantially off when said device is off and on when said device is on. ### Claim 8 (depends on 1) The apparatus as claimed in claim 1, further comprising a driver configured to drive said device, said control signal being provided to a control circuit of said driver. ### Claim 9 (depends on 1) The apparatus as claimed in claim 1, further comprising a switch for controlling the switching on and off of said device, said control signal causing said switch to switch off said device. ### Claim 10 (depends on 1) The apparatus as claimed in claim 1, further comprising a clamp switch arranged across said device, said clamp switch when on is configured to cause first and second nodes on either side of said device to be at substantially the same voltage to cause said device to be off, said control signal causing said clamp switch to be on. ### Claim 11 (depends on 1) The apparatus as claimed in claim 1, wherein said device comprises a laser diode. ### Claim 12 (depends on 1) The apparatus as claimed in claim 1, wherein the device comprises a light emitting diode. ### Claim 13 (depends on 1) The apparatus as claimed in claim 1, wherein the first current is greater than the second current when the device is switched on. ### Claim 14 (depends on 1) The apparatus as claimed in claim 1, wherein the first current is less than the second current when the device is switched off. ### Claim 15 (depends on 1) The apparatus as claimed in claim 1, wherein the monitoring circuit comprises: a counter configured to receive the first output, the counter being further configured to generate the control signal in response to the first output being at a binary level for more than a threshold number of counts.