Lecture 3 Mixed Signal Testing

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
• 0.1-1.0mA 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

• ZV/I (Usually ZDV/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 (V1V2)/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