Test Generation for MixedSignal Circuits Using Testability Analysis

1
Test Generation for Mixed-Signal Circuits Using
Testability Analysis

• M. Stancic and H. G. Kerkhoff
• MESA Research Institute / University of Twente
• CADTES/TDT Group
• The Netherlands

ETW 2002, Corfu
2
Outline

• Introduction
• Definition of the TTF
• Testability measures
• Testability analysis
• Test pattern generation
• Conclusions

3
Introduction

• Introducing measures for controllability and
  observability of nodes in the circuit theory have
  been necessary, because testability of a circuit
  is directly related to them
• A new definition of the testability transfer
  factor for circuit components that provides
  better sensitivity with regard to parametric
  deviations is introduced
• New equations for controllability and
  observability of nodes are derived

4
Definition of the TTF

• The TTF of a component represents
• the easy of achieving an arbitrary signal on its
  outputs by exercising its inputs
• the easy of determining whether a specific signal
  occurred on its inputs by examining the values on
  its outputs

5
Definition of the TTF
a
b
Z(w)
a
b
T(Z(w))
6
Definition of the TTF

• In order to increase the sensitivity for low
  impedances, a new definition of the testability
  transfer factor of a frequency dependent
  impedance Z (w) is given

7
The TTF for different values of the parameter a
8
Deviation of the TTF as function of the component
deviation for a1
9
Testability measures

• The controllability of a node in a circuit
  represents the ease of applying an arbitrary
  signal value at that node by full control of the
  primary inputs.
• The observability of a node represents the ease
  of determining whether or not the expected signal
  value occurs at the node by observing the signal
  values at the primary outputs of the circuit.

10
Why new Testability measures/analysis?

• Derived test patterns are very complex for
  practical generation

11
Testability measures
12
Testability Analysis

• Transformation of the circuit into the SFG
• Calculation of the testability for all nodes for
  all frequency range
• Solution for circuits with multiple
  inputs/outputs

13
Example circuit
14
Example circuit / SFG
15
Test pattern generation

• The fault list bridging faults between nodes and
  interconnection faults modeled by a serial
  resistance
• The error function difference between the
  testability for the faulty and the fault-free
  case
• If the error function for a frequency is under a
  predefined threshold, than that test signal
  frequency can be used for detecting that fault in
  the circuit

16
Signature for a faulty and fault-free circuit for
a bridging fault (D05-XPD).
faulty
f450kHz
f450kHz
17
Signature for a faulty and fault-free circuit for
a interconnection fault (D04).
f850kHz
18
Example circuit II
19
Test responses of the filter for fault-free and
faulty case for a bridging fault observed on the
band-pass output (out_BP)
faulty
f16.5kHz f211.5kHz
20
Conclusions

• new definition for the TTF for circuit components
  is introduced
• new equations for the C/O of nodes in a
  mixed-signal circuit are proposed
• Major improvement reduction in CPU time