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Lecture 3 Mixed Signal Testing

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Presentation on theme: "Lecture 3 Mixed Signal Testing"— Presentation transcript:

1 Lecture 3 Mixed Signal Testing
DC and Parametric Test

2 Continuity Testing Detect on-chip ESD devices
Validate Connection of Device to Tester Eliminate DC Package Bridging Faults mA current (over voltage) Parallel testing to speed process Current Limit Test Accuracy

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

4 Power Test II Testing over Operation Range
(Schmoo Plots): Voltage/Current/Freq Earliest form of Binning Memory devices Processors

5 Impedance Measurement
Z=V/I (Usually Z=DV/DI) Force V, measure I (High Impedance) Force I, Measure V (Low Impedance) Defined Testing Levels Reduce possibility of DUT damage Increase accuracy of measurement

6 DC Transfer Characteristics
Offset Input or Output Referenced

7 Tester Loading Impedance
Input impedance of tester is not infinite Possibility of substantial error

8 Output Offset Definition
Single Ended: relative to reference Differential: Common Mode (V1+V2)/2 Differential Mode (V1-V2)

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

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

11 Nulling Amplifier

12 Power Supply Rejection
Input held constant

13 Power Sensitivity Measurement

14 Common Mode Rejection Ratio
Measure Offset Voltage Similar problem to Gain – need servo loop

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

16 Digital DC Tests Iih/Iil Leakage Vih/Vil Thresholds Ioh/Iol Drives
Short Circuit Currents

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