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DFT Scan Types And Their Mechanism

As Design Complexity increases, there are a number of challenges such as higher test costs, higher power consumption, pin count, and new defects at small geometries. So, as VLSI technology shrinks to lower technology nodes, we need efficient techniques for testing on lower nodes. Both reliability and testability are critical criteria in today’s VLSI design. For this, we employ design for testability. In this post, we will explore more about DFT scans, DFT Scan types, etc. 

What is DFT Scan?

DFT scan is a technique used in digital circuit design to facilitate the testing and debugging of integrated circuits (ICs). The DFT scan methodology involves modifying the circuit design by adding extra logic to enable the capture and output of internal states for testing purposes. The DFT scan technique involves dividing the circuit into a series of smaller units called scan chains. Each scan chain is made up of a set of flip-flops connected in a serial configuration, with additional control logic to enable the scan operation. The scan chains are used to capture the internal state of the circuit, which can then be output for analysis and testing.

DFT scan is an essential part of modern IC design, as it enables comprehensive testing of the circuit to ensure that it meets its specifications and is free of defects. Without a DFT scan, it would be much more challenging and time-consuming to test and debug complex digital circuits.

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What Are DFT Scan Types?

Design for Testability (DFT in VLSI) is a set of techniques used in electronic design to improve the ease and efficiency of testing electronic systems. There are several types of DFT scans that can be performed:

  1. Full Scan: In full scan, all flip-flops in the circuit are connected in a scan chain, allowing for the capture and output of all internal states. 
  2. Partial Scan: In partial scan, only a subset of the flip-flops in the circuit are connected in a scan chain, typically those that are most difficult to test. This technique reduces the test data volume and test time.
  3. Scan Chain Insertion: This involves adding scan chains to the design, which allows the state of the design to be easily captured and analyzed during testing.
  4. Boundary Scan Insertion: This involves adding boundary scan cells to the design, which allow the inputs and outputs of the design to be accessed and tested.
  5. Functional Test Insertion: This involves adding specialized circuitry to the design, which can be used to test specific functionality or features of the design.
  6. Analog and Mixed-Signal Test Insertion: This involves adding specialized circuitry to the design, which can be used to test the analog and mixed-signal components of the design, such as analog-to-digital converters (ADCs) and digital-to-analog converters (DACs).

The goal of DFT is to make it easier and more efficient to test electronic designs, which can help reduce time-to-market and improve the reliability and quality of electronic systems.


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