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Design+ Defect-oriented BIST for AMS circuits

tests. It should also be emphasized that rigorous post- These invariants should fall within an acceptable, defect-
manufacturing tests are expensive endeavors, especially free range; any violation of this range indicates the
considering the cost-sensitive nature of the automotive detection of a defect. The most important feature of this
semiconductor industry. Therefore, system designers are approach is the transparency of the BIST with respect
increasingly compelled to employ built-in self-test (BIST) to the main circuit. However, the approach is tested for
solutions. This not only reduces testing time and costs but a selected set of defects and has overall average defect
also significantly enhances the functional safety of ICs by coverage of 87.56%. Another work was presented by Das
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enabling in-field health monitoring of the devices. et al., in which the analog circuit was broken down into
small circuits of operational amplifiers, comparators, phase
Based on the failure reports, nearly 80% of the in-field IC
failures are due to malfunction in analog and mixed signal lock loops (PLL), and filters. These subcircuits were then
(AMS) circuits. Considering the fact that AMS circuits converted to oscillators by adding proper circuitry. Defects
5,6
comprise only 20% of the area in a general system on chip were detected by comparing the oscillation parameters
(SoC) but are responsible for 80% of the failures, makes the with the nominal values. This work represents one of
functional safety and reliability concerns in AMS circuits the early endeavors in AMS structural testing, providing
a solution for AMS reliability concerns. However, it
are even more critical. This significant difference between necessitates circuit alterations and the addition of resistive
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the reliability performance of the AMS circuitry and their and capacitive components, which can pose challenges for
digital counterparts primarily comes from the nature of implementation as a BIST or online testing method.
AMS circuitry, making the development of structural tests
for these circuits a challenging task. In this paper, we introduce a structural defect-oriented
test for AMS circuits, solely utilizing digital monitoring
Over the past few decades, several methods and circuits. This approach achieves 100% defect coverage
strategies have been introduced, developed, and advanced without altering the circuit’s topology and incurs with a
for defect-oriented structural testing of digital circuits. minimum area overhead. In this approach, we first identify
In addition, several standards have been developed to the critical nodes of the circuit, and then we develop a
systemize these tests for digital circuits. However, AMS test mechanism using external injector circuitry or by
circuits have been and mostly still are being tested only operating the circuit itself in a specific test mode. Finally,
for characteristic performance. The lack of a systematic using digital monitors, the occurrence of defects is detected
structural test for AMS circuits is largely due to the nature by changes in the digital output of monitors from defect-
of these circuits. When a defect occurs in AMS circuits, it free code to faulty code. The proposed test method can be
often results in only a slight deviation from the nominal employed as a post-manufacturing test or as an in-field
expected value, which still falls within the desired, structural test targeting the latent defects. The proposed
acceptable range and may be crossed out as the result of method is demonstrated on the successive approximation
the process, voltage, and temperature (PVT) variation. register (SAR) analog-to-digital converter (ADC), as a case
However, in the long run, it is these seemingly innocuous study. We performed a full structural test on a 12-bit ADC
defects that might result in a latent failure of the said designed in a 65 nm technology node.
circuit block or even the entire IC as the IC faces harsh
environmental conditions in the field. As an example, in The rest of the paper is organized as follows. In section
the automotive industry, most in-field IC failures happen II, the approach to the digital-like built-in structural test
after thousands of kilometers of driving. Therefore, though for AMS circuits is discussed. In section III, we discuss
structural defects in AMS circuitry may not significantly the defect universe and simulation method for high-
affect the IC’s characteristics initially, rendering them speed defect coverage test. We demonstrate the proposed
invisible during the characteristic testing, they need to be structural test for SAR ADC in section IV. Section V will
detected, nonetheless. This lack of a structural test for AMS include the simulation results of the defect-oriented BIST
circuits and their impact on IC reliability has recently made for SAR ADC based on the proposed method. Finally,
defect-oriented testing for AMS circuits a hot topic, 3,7,8 section VI concludes the paper.
leading to the ongoing development of IEEE 2427 standard
for addressing this issue. 9 2. Materials and methods
As mentioned, little research has been performed 2.1. Digital-like defect-oriented test
on developing structural defect-oriented tests for AMS As mentioned earlier, developing a defect-oriented BIST
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circuits. Among the few is SymBIST, which introduces for AMS circuits is a challenging task. Part of the challenge
a BIST based on the inherent or pseudo symmetries in a lies in adhering to the general principals of developing
circuit that can generate values referred to as invariant. BIST for any type of circuit, regardless of its domain of

Volume 1 Issue 1 (2024) 2 doi: 10.36922/dp.4351