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Grasp LVDS and automated measurements (Part 2)

Posted: 31 Aug 2015     Print Version  Bookmark and Share

Keywords:LVDS  microcontroller  LabVIEW  oscilloscope  FLASH memory 

Today's vehicles employ TFT LCD displays for presenting the vehicle's status, entertainment system, and other information to the driver. The displays are driven by an SoC that contains memory, an control unit, and a bridge that delivers a serial low voltage differential signalling (LVDS) data stream. LVDS lets us achieve high speed data transfer with high signal integrity and low power consumption.

In Part 1, I described the LVDS signalling standards and the architecture of LVDS module used in a microcontroller. The signal specifications need robust characterisation and functional tests to avoid field failures. In part 2, I'll describe which instruments are needed for characterisation and how to automate measurements.

Hardware used:
 • SoC Development Board
 • P&E Debugger: Lauterbach Debugger to load DUT Code into SoC
 • Power Supply: Keysight E3648A
 • Digital Multimeter for DC Characteristics. You can use a meter from any manufacturer
 • UART Cable to run several test cases
 • Source-measure unit for leakage current measurements
 • Digital Serial Analyser: Tektronix (50 GS/s with 16GHz Bandwidth
 • Differential probes

Software used:
 • LabVIEW 2012
 • Trace32 for LauterBach Debugger
 • ARB Express Signal Generator
 • TINA TI for simulations
 • GHS Code Compiler
 • P&E Debugger Software
 • Automation process

LabVIEW based automation is used to sequence the test case and data acquisition routines. An oscilloscope acquires the LVDS signals. The instruments preferably should have GPIB for automation. Figure 1 gives a flowchart of the automation. Figure 2 shows the process in flowchart form.

Figure 1: This LabVIEW VI shows the automation process in code form.

Figure 2: Test automation flowchart.

The above automation process helps us automatically carry out the desired tests under various temperature and voltage conditions. Initially, a GPIB signal is sent to all the hardware devices, which establishes control through LabVIEW and sets up communication between the SoC and the test instruments. A temperature loop operates the SOC on various temperature levels. We also use a voltage loop to operate the SoC under various voltages. We then load DUT code into the SoC. The Digital Serial Analyser measures the desired parameters using LabVIEW and stores the report with desired parameters. The data from the report is then imported into an Excel sheet for further Analysis. Both the DC and AC Characteristics are carried out using the Automation processes done using LabVIEW.

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