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[TEST] Laser Diode Current Output Temperature Coefficient #44

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opened 2024-04-26 15:08:53 +08:00 by linuswck · 0 comments
linuswck commented 2024-04-26 15:08:53 +08:00
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Objective

To investigate laser diode output current drift under the change of ambient temperature.

Test Setup

Hardware

Kirdy Rev0_3 with no LD adapter installed

The LD output current is controlled by MAX5719 20bit DAC being connected with LTC6655 4.096V Reference
The LD Drive Circuit has a transimpedance of 10.0/0.75 (1/Ohm)

Firmware:

A Custom firmware based on commit b8241d1f27

  • AD7172-2 has a built-in temperature sensor. It is located far away from the major heat source so it can be use as a reference for the ambient temperature.
  • Firmware is modified to read the AD7172-2 Temperature Sensor and report it via debug console and report for data logging.
  • AD7172-2 Filter Settings
    • Temperature Sensor: Sinc5Sinc1 Filter 31,250SPS -> 6211SPS (as multiple channels are enabled)
    • Laser Diode NTC: Sinc5Sinc1 with Enhanced 50 Hz and 60 Hz Rejection Filters: 16.667SPS

Test Equipment

Agilent 34401A Multimeter (Not re-calibrated since manufacturing)

  • Measurement Mode: DC Current Mode with 6.5 Digit Measurement
  • Integration Time: 100 PLC
  • Input Range: 0-100mA
  • Internal Shunt Resistance: 5 Ohm

A Temperature Controlled Oven is used to heat up the air around the board evenly

Circuit Connection:

  • LD+ and LD- are connected directly to the Multimeter

Output Setting

Thermostat: Turned OFF
Laser Diode Output Current: 50mA

Result

Board Temperature (Degree) Current (mA)
43.1801299361277 50.0277
47.0413065928144 50.0263
49.102155476 50.0257
51.0310358622754 50.025
51.5556305968064 50.0249
55.903212552 50.0235

Controllable Range = 307.2mA
Temperature Coefficient = -0.328713232975702(uA/Degree) = -1.122007 (LSB/Degree) = -1.07003005525945 (ppm/Degree)
Note: Calculated with Linear Regression

Temperature Reading Cross Checked:
Fluke 87V: 46.2 Degree
Temperature Reading on the Oven: 46.2 Degree
Kirdy Board Temperature Reading: 45.072815 Degree

(Edited1 : Add ppm calculation)
(Edited2: Add temperature readings comparison with different instruments)

# Objective To investigate laser diode output current drift under the change of ambient temperature. # Test Setup ## Hardware Kirdy Rev0_3 with no LD adapter installed The LD output current is controlled by MAX5719 20bit DAC being connected with LTC6655 4.096V Reference The LD Drive Circuit has a transimpedance of 10.0/0.75 (1/Ohm) ## Firmware: A Custom firmware based on commit [b8241d1f27](https://git.m-labs.hk/M-Labs/kirdy/commit/b8241d1f27dcaf04cb218cfac6abe151745c48ff) - AD7172-2 has a built-in temperature sensor. It is located far away from the major heat source so it can be use as a reference for the ambient temperature. - Firmware is modified to read the AD7172-2 Temperature Sensor and report it via debug console and report for data logging. - AD7172-2 Filter Settings - Temperature Sensor: Sinc5Sinc1 Filter 31,250SPS -> 6211SPS (as multiple channels are enabled) - Laser Diode NTC: Sinc5Sinc1 with Enhanced 50 Hz and 60 Hz Rejection Filters: 16.667SPS ## Test Equipment Agilent 34401A Multimeter (Not re-calibrated since manufacturing) - Measurement Mode: DC Current Mode with 6.5 Digit Measurement - Integration Time: 100 PLC - Input Range: 0-100mA - Internal Shunt Resistance: 5 Ohm A Temperature Controlled Oven is used to heat up the air around the board evenly ## Circuit Connection: - LD+ and LD- are connected directly to the Multimeter ## Output Setting Thermostat: Turned OFF Laser Diode Output Current: 50mA # Result | Board Temperature (Degree) | Current (mA) | |---|---| | 43.1801299361277 | 50.0277 | | 47.0413065928144 | 50.0263 | | 49.102155476 | 50.0257 | | 51.0310358622754 | 50.025 | | 51.5556305968064 | 50.0249| | 55.903212552 | 50.0235| Controllable Range = 307.2mA Temperature Coefficient = -0.328713232975702(uA/Degree) = -1.122007 (LSB/Degree) = -1.07003005525945 (ppm/Degree) Note: Calculated with Linear Regression Temperature Reading Cross Checked: Fluke 87V: 46.2 Degree Temperature Reading on the Oven: 46.2 Degree Kirdy Board Temperature Reading: 45.072815 Degree (Edited1 : Add ppm calculation) (Edited2: Add temperature readings comparison with different instruments)
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