Page 73 - Building A Succesful Board-Test Strategy
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Jest Methods 59
Board-Test Categories
* Shorts and opens
* Manufacturing defects analyzer
* In-circuit
* Functional
* Combinational
* "Hot mockup"
* Emulation
* System
Figure 2-3 Electronics manufacturers select test strategies that include one or more of
these test techniques.
R M —
—
Figure 2-4 The "apply voltage, measure current" in-circuit measurement technique.
the process remains in control and that no random problems get through the
monitoring steps.
Electronics manufacturers select test strategies that include one or more of
the techniques listed in Figure 2-3. The following sections will explore each test
technique in detail. The next chapter will address the issue of inspection.
2.3.I Analog Measurements
Bed-of-nails~based automatic test equipment generally performs analog mea-
surements using one or both of the operational-amplifier configurations shown in
Figures 2-4 and 2-5.
In each case, the operational amplifier, a high-gain difference device featuring
high-impedance inputs and a low-impedance output, serves as a current-to-voltage
converter. Both versions tie the positive input to ground. Because (ideal) op-amp
design requires that the two inputs be at the same potential, the amplifier is stable
only when the negative input is at virtual ground and no current flows at that point.
