Tektronix partner Ketai released: 3D sensing VCSEL array test solution based on TOF technology
What is TOF technology for 3D sensing?
A TOF sensor measures the time it takes for light to travel a certain distance in a medium. Typically, this is a measurement of the time it takes for a pulse of emitted light to reach an object and reflect back to the TOF sensor. A TOF camera uses the TOF measurement principle (TOF image sensor) to determine the distance between the camera and an object or surrounding environment, and generates a depth image or 3D image from the measured points.
What is a Passive VCSEL Array?
Passive VCSEL array refers to a VCSEL array device without a driver circuit. When VCSEL arrays are used for 3D sensing of TOF technology, the rise and fall time characteristics of the light pulses emitted by the sensing system are very important, especially for dTOF, TR/TF directly affects the performance of the final product .
For passive VCSEL arrays, their transient response is usually very good, reaching hundreds of ps or even tens of ps. However, since they are driven by large currents, it is very difficult to measure their true TR/TF. This depends on the capabilities of the driver and test system used for testing, as well as the design selection of the driver circuit, the link length between the driver and the device under test, the operating point and matching adjustment, etc.
Currently, common TR/TF tests are mainly used in R&D and verification of a limited number of single devices. The main test method used is to solder the device on a customized (or final use) driver circuit board, using a high-speed PD and a high-bandwidth oscilloscope. Due to the use of a soldering connection, this test is destructive, meaning that the device under test cannot be used in the product later; and soldering and removing the device under test is time-consuming and labor-intensive, so there are usually not many test samples .
On the other hand, the TR/TF test using an external driver board essentially tests the TR/TF of the “driver board + VCSEL array” rather than the “TR/TF of the VCSEL array”. Therefore, this test is an evaluative test and may not reflect the true performance of the VCSEL array (unless the driver capability is much higher than that of the VCSEL array being tested).
Based on the current status of TR/TF evaluation test of passive VCSEL arrays, and taking into account the versatility, convenience and repeatability of the test, Tektronix partner Kotek Test has developed a test system based on universal drivers and universal instruments .
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The main target scenarios for using this test system include:
- 3D sensing module research and development
- Array module packaging test
- 3D sensing system manufacturers' incoming material inspection and failure analysis
- VCSEL chip performance evaluation
Test System Overview
The test system components mainly include:
· General purpose narrow pulse driver
Multi-channel power supply to control the driver operating conditions
Universal pulse signal source
High - speed photodetector
Broadband Oscilloscope
Automatic testing software
Replaceable test fixture
Other test accessories, such as light attenuation sheets, light shielding boxes, high-frequency cables, etc.
The main features of the test system are:
Use customized test fixtures to achieve non-destructive rapid testing
Adapt to different DUTs by adjusting the working conditions of the driver board
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Using universal test instruments, the controllability and repeatability of test conditions are better than traditional customized systems. The instruments in the system can also be used in other tests, with good versatility.
Small
integrated test bench to improve system building efficiency
One
-click automated testing software automatically scans working points to improve work efficiency
Test
system components can be replaced as needed to achieve higher test requirements
System Configuration and Indicators
System Configuration:
A typical configuration of this system (KAS-NPT1500 rack model) includes:
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Four-channel oscilloscope with bandwidth no less than 1.5 GHz
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High-speed spatial light detector with bandwidth no less than 1.4 GHz
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Arbitrary function generator (AFG) with a frequency range of at least 240 MHz
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Three-channel programmable DC power supply
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CTA-NPD12 narrow pulse driver board
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CTA-LTC1 Laser Test Bench
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Customized fixtures according to the test piece
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Automatic test software KTS-TRTF-A01
TR/TF indicator:
Under typical configuration, the test system can achieve typical TR/TF index parameters as shown in the following table:
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index |
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Minimum rise and fall time |
<300ps |
20~80%
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3ns
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(Note 1: Based on the actual test results of limited samples, the test uses a universal fixture. There may be better performance in actual use. In addition: This system supports welding, and better performance may also be obtained during welding)
(Note 2: Other main indicators, such as operating current, voltage, etc., will be given in the subsequent "Narrow Pulse LIV Test System Specifications")
Test Bench:
The CTA-LTC1 laser test bench is suitable for laboratory environments and provides multiple structures such as driver fixation, PD positioning, filter switching, shading, cable connection, etc., which can quickly build an experimental environment. Its external dimensions are 330mm x 330mm x 600mm (excluding support feet).
CTA-LTC1 Test Bench
Automatic test software KTS-TRTF-A01
In the TR/TF evaluation test system of the passive VCSEL array, the working conditions of the driver have a significant impact on the results of the TR/TF test. At the same time, when the same driver works with different DUTs, its optimal working point will also change.
The universal driver board provided in this test system needs to be carefully tuned to cooperate with the device under test to obtain the best TR/TF results. KTS-TRTF-A01 automatic test software provided by KTS-TEST can complete this delicate and tedious work. Based on the professional understanding of test instruments and in-depth analysis of test methods, we select the best instrument combination, supplemented by detailed triggering mode, sampling mode and measurement parameter settings, so that users only need to provide the relevant scanning range of the working point, and the software can present the recommended value of the best working point in a list. Then, the user only needs to double-click the setting in the recommended list to complete the corresponding test setting selection.
Automated testing software example
Currently, the list of instruments supported by this software is as follows:
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Oscilloscope |
Tektronix MSO4 Series, MSO5 Series, MSO6 Series |
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power supply |
Tektronix, Keithley, Itech full range of programmable DC sources |
For more information about our products and applications, you can also contact us via the following methods:
Email: china.mktg@tektronix.com
Website: www.tek.com.cn
Tel: 400-820-5835 (Monday to Friday 9:00-17:00)
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