UnitTest

The procedures below used SDR (Software Defined Radio) as a case study which summarized the testing process & ideas through the whole design process as a reference for future design.

Breadboard Level Testing

Unit Testing

Purpose

• When subsystems are assembled / compiled, they are ready for unit testing.

• Unit testing determines if you satisfied the requirements as set out by ICD and the design proposal

2. Pre-Test Tips

• polarity connection

  •  be careful about positive & negative terminals to avoid backword connection to damaged & rendered usability of main board

• install one PCB at once

  • this depends on the testing plan (some plan settings and test board assume all other PCBs are absent)

• set current limit on power supply

  • Normally, a current limit of 100 ~ 200 mA is enough

  • before powering up, set a constant voltage & a current limit on PC, then turn on the switch 

    • correct output ✅ : PC stays in CV mode, current shows a small & expected value (50 mA)

    • wrong output 🚨: PC immediately switches to CC mode, huge voltage drop, current hits the limit, smells hot

-> solution: shut it off right away, look for shorted power rails, any wrong orientation,  measure VCC ~ GND resistance 

• Need for Dummy Load?

  • made by precision resistor & heat sink,  important to consider when test power amplifier & RF circuit individually

  • electrically acts like an antenna (real load) but doesn't radiate

  • purpose:

    • impedance matching -> avoid signal reflection, stress damage, high voltage standing wave ration (VSWR)

    • actively pushing circuit current (power) into the dummy load as an output

    • prevents thermal runaway (unintended RF radition) or oscillation ( unstable operation & teminatio)

• Collection of Usable Procedures:

  • Testing without switch installed:

    • use jump wite, hard-wire the output, observe the signal there

  • Set output termination:

    • For CMOS & Oscilloscope, use High - Z -> so function generator assumes it's driving a high-impedance load, correctly deliever and display the intended signal

    • otherwise: wrong load, wrong output voltage, oscilloscope may display double the expected amplitude

  • when signal frequency > = 10 MHz:

    • select "sine wave" at "waveform" ,  the function generator cannot generate non-sinusoidal signals with a frequency higher than 10 MHz -> even if  I want a square wave

  • when systems  exist  multi-input signals  (eg. 3.3v, 5v):

    • identify the  function of siganls  (3.3v  controls  high & low stage,  5v is power signal), and what should respond

    • first, set 3.3v high & disable other parts of circuit (eg. PA), discover current draw + set 3.3v low, repeat

    • enable function generator observe the output -> calculate power

  • total harmonic distoration (THD):

    • use FFT by automation scripts

    • measure the amplitudes of various harmonics (n >= 5) for various output power
      
      
      

Integration Testing