Download Lecture 3 Mixed Signal Testing

Lecture 3 Mixed Signal Testing
DC and Parametric Test
Continuity Testing
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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
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Current Limit
Test Accuracy
Power Supply Test: Iddq
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Many manufacturing defects result in
abnormal power current
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Metal Errors – shorted traces
Implant/Diffusion errors – shorted
substrate
Faulty ESD Clamps
Open/Floating Wells
Open/Floating Digitial gate input
Power Test II
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Testing over Operation Range
(Schmoo Plots): Voltage/Current/Freq
Earliest form of Binning
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Memory devices
Processors
Impedance Measurement
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Z=V/I (Usually Z=DV/DI)
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Force V, measure I (High Impedance)
Force I, Measure V (Low Impedance)
Defined Testing Levels
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Reduce possibility of DUT damage
Increase accuracy of measurement
DC Transfer Characteristics
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Offset
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Input or Output Referenced
Tester Loading Impedance
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Input impedance of tester is not infinite
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Possibility of substantial error
Vmeasured  (
Rin
)Vactual
Rin  Rout
Output Offset Definition
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Single Ended: relative to reference
Differential:
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Common Mode (V1+V2)/2
Differential Mode (V1-V2)
Input Offset
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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
Measuring Gain
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For practical Op-Amps, gain is high
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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
Nulling Amplifier
 R1  R2  DVsrc
DVo
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G
 
DVin
 R1  DVnull
Power Supply Rejection
DVout
Sensitivity 
DVdd
Vin
Sensitivity
PSRR 
Gain
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Input held constant
Power Sensitivity
Measurement
Common Mode Rejection Ratio
GCM
DVO
DVOS
CMRR 
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GD
DVCM GD
DVCM
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Measure Offset Voltage
Similar problem to Gain – need servo
loop
Voltage Search
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Need to set input to fix complex output
Three ideas:
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Step Search (Ramp)
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Binary Search (Faster)
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Issue (Cost of test)
Issue (Hysteresis of DUT or Tester)
Linear Search (Simplified form of Newton)
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Needs Computerized Tester
Digital DC Tests
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Iih/Iil Leakage
Vih/Vil Thresholds
Ioh/Iol Drives
Short Circuit Currents