Abstract
The preceding chapters of this book have confined the discussion to digital circuits and test subjects. Most electronic engineers are experts in digital technology but many will admit that their familiarity falls off quickly when the discussion turns to analog topics, particularly analog testing. Before getting into IEEE 1149.4 Analog Boundary-Scan, it will be important to lay a foundation for basic analog measurements used today in In-Circuit testers. While 1149.4 does have significant differences over classical In-Circuit test, there are a lot of similarities. Knowing where we came from will also help motivate where we are now going.
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Notes
- 1.
Real components, not parasitics.
- 2.
As we will see later in this section, we also have to be careful of other devices surrounding the device we are testing.
- 3.
There is the case where the impedance is infinite because of an open circuit. In this case the process of finding a current setting will converge on zero.
- 4.
It is possible that the search would converge on zero volts in the case where the value of R was zero, such as in the case of a short circuit.
- 5.
Not shown in this figure are Electrostatic Discharge (ESD) protection diodes often found between IC pins and the power rails. These diodes can provide additional conduction paths if they turn on.
- 6.
The switching time from open to closed is less than perfect, in the neighborhood of 500 microseconds. They often take longer to open.
- 7.
An example at the macroscopic level of Heisenberg’s Uncertainty Principle. To measure the value of a component with this technique, we must significantly perturb the circuit under test.
- 8.
Relays will have sub-ohm resistances typically, but nail contacts may have resistances of 2 Ω and higher depending on the cleanliness of the nail and board surfaces. Nail contact resistance may increase with time but may be restored by periodic cleaning of nails .
- 9.
Remember that because of its very high input impedance, the insertion of the voltmeter will not seriously affect the current flow of the circuit.
- 10.
This capacitor doesn’t need to be accurate (only stable over the period of measurement) but it should have excellent characteristics with respect to dielectric absorption.
- 11.
This region will be within the power supply rail voltages of the operational amplifier .
- 12.
To limit effects from environmental noise, we may restrict the values of T to those that will mask out common sources such as low frequency power line noise.
- 13.
Actually, switches D and E are conceptual. The AC voltages are digitally constructed by the system sources. The system has complete on-the-fly control of the frequency and phase.
- 14.
Imaginary signal detection is sometimes called a quadrature measurement.
- 15.
The techniques shown here work for higher numbers of nodes and components. However it is difficult to visualize higher-order dimensions.
- 16.
Using AC voltages, we can also determine if a different type of component, for example, a capacitor, has been misloaded in place of a resistor. With extreme miniaturization, many components look the same and do not have enough space on them for labels.
- 17.
One node is always used as the reference node for voltage measurements.
- 18.
Indeed, it is possible to have a single signal with both natures. Consider for example the encoding of digital information within an analog television signal, used for closed-captioning.
- 19.
“Continuous” means non-quantized, to differentiate analog signals from multiple-valued logic signals that are still essentially digital in nature.
- 20.
Printed circuit dimensions are often specified in English (Imperial) units. A “mil” is 0.001 in., or about 25 μm.
- 21.
Consider a board requiring 4000 nails , each with 0.5 lb of spring force. That comes to 2000 lb (nearly 1 metric ton) of spring force distributed across a board and fixture .
References
“Analog In-Circuit Component Measurements: Problems and Solutions”, D. T. Crook, Hewlett-Packard Journal, vol 30, No. 3, March 1979
“Analog Fault Diagnosis for Unpowered Circuit Boards”, J. L. Huang and K. T. Cheng, Proceedings, International Test Conference, pp 640–648, Washington DC, Nov 1997
“Limited Access Testing: Ability and Requirements”, J. McDermid, Proceedings, NEPCON 1998, Anaheim CA, Feb 1998
“Solving Limited Access Constraints in ICT”, J. McDermid, Electronics Engineer, July 1998
“Limited Access Testing: 1149.4 Instrumentation and Methods”, J. McDermid, Proceedings, International Test Conference, Washington DC, Oct 1998
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Parker, K.P. (2016). Analog Measurement Basics. In: The Boundary-Scan Handbook. Springer, Cham. https://doi.org/10.1007/978-3-319-01174-5_6
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