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Lecture 3 Mixed Signal Testing DC and Parametric Test Slide 2 Continuity Testing Detect on-chip ESD devices Validate Connection of Device to Tester Eliminate DC Package Bridging Faults 0.1-1.0mA current (over voltage) Parallel testing to speed process Current Limit Test Accuracy Slide 3 Power Supply Test: Iddq Many manufacturing defects result in abnormal power current Metal Errors shorted traces Implant/Diffusion errors shorted substrate Faulty ESD Clamps Open/Floating Wells Open/Floating Digitial gate input Slide 4 Power Test II Testing over Operation Range (Schmoo Plots): Voltage/Current/Freq Earliest form of Binning Memory devices Processors Slide 5 Impedance Measurement Z=V/I (Usually Z= V/ I) Force V, measure I (High Impedance) Force I, Measure V (Low Impedance) Defined Testing Levels Reduce possibility of DUT damage Increase accuracy of measurement Slide 6 DC Transfer Characteristics Offset Input or Output Referenced Slide 7 Tester Loading Impedance Input impedance of tester is not infinite Possibility of substantial error Slide 8 Output Offset Definition Single Ended: relative to reference Differential: Common Mode (V1+V2)/2 Differential Mode (V1-V2) Slide 9 Input Offset Voltage (Current) needed to set output voltage (current) at reference level In theory can measure ouput offset and divide by gain In practice gain often too high device output is pinned to rail Slide 10 Measuring Gain For practical Op-Amps, gain is high Use Nulling amplifier and resistor divider Null Amplifier acts as servo to drive ouput voltage to known reference Resistor divider acts to lower input sensitivity Need Loop Compensation Want Divider ratio similar to expected Gain Can get input offset as well by choosing null reference goal Slide 11 Nulling Amplifier Slide 12 Power Supply Rejection Input held constant Slide 13 Power Sensitivity Measurement Slide 14 Common Mode Rejection Ratio Measure Offset Voltage Similar problem to Gain need servo loop Slide 15 Voltage Search Need to set input to fix complex output Three ideas: Step Search (Ramp) Issue (Cost of test) Binary Search (Faster) Issue (Hysteresis of DUT or Tester) Linear Search (Simplified form of Newton) Needs Computerized Tester Slide 16 Digital DC Tests I ih /I il Leakage V ih /V il Thresholds I oh /I ol Drives Short Circuit Currents