What is scan flip-flop?

What is scan flip-flop?

A scan flip-flop is a D flip-flop with a 2×1 multiplexer added at its input D. one input of the MUX acting as the functional input D when SE/TE=0 and the other input serving as the Scan-In (SI) input when SE/TE=1. Scan/Test Enable (SE/TE) is used to control the MUX i.e used as selection bit.

How does scan chain work?

SCAN CHAIN Scan chain acts as a shift register when the design is in test timing mode; SE (test enable signal) is active. The first flip-flop of the scan chain is connected to the scan input port and the last flop the scan chain is connected to the scan output port.

What is scan chain insertion?

Scan chain is a technique used in design for testing. The objective is to make testing easier by providing a simple way to set and observe every flip-flop in an IC. The basic structure of scan include the following set of signals in order to control and observe the scan mechanism.

What is scan chain balancing?

Scan chain balance the scan vector length will depend on longest chain – increase in test time. and also, the other shorter vectors must be X-filled at the front – wastage in tester memory. it is best to divide the FFs into scan chains in such a way as to leave only one short scan chain if there are any FFs left over.

What is the purpose of scan testing?

Scan testing is done in order to detect any manufacturing fault in the combinatorial logic block. In order to do so, the ATPG tool try to excite each and every node within the combinatorial logic block by applying input vectors at the flops of the scan chain.

Why do we need scan insertion?

SCAN insertion architecture helps to test each of the logic elements in the IC irrespective of its position by inserting test vectors to device pins.

What is scan insertion and what is the need of it?

To enable a scan test for a chip design, additional test logic must be inserted; this is called “scan insertion”. Scan insertion consists of two steps: 1. Replace plain memory cells like flipflops or latches by scan cells. 2.

Why is DFT scan needed?

Scan is the first step for inserting DFT(design for testability) architecture in any chip. Thus scan insertion improves the controllability and observability of the sequentially flops.

Why do we need to scan chain reordering?

Scan chain reordering is a process used in the design and testing of computing devices that enables the optimization of placing and stitching flip flop registers with a scan chain. It is used to optimize and reorder the scan chain process if it gets detached, stopped or congested.

What is lockup latch?

A lock-up latch is a transparent latch used to avoid large clock skew and mitigate the problem in closing hold timing due to large uncommon clock path.

What is DFT scan?

Overview. Design for testability (DFT) makes it possible to: ■ Assure the detection of all faults in a circuit. ■ Reduce the cost and time associated with test development.

What is scan operation in DFT?

So the industry moved to a design for test (DFT) approach where the design was modified to make it easier to test. The approach that ended up dominating IC test is called structural, or “scan,” test because it involves scanning test patterns into internal circuits within the device under test (DUT).

What is scan def in VLSI?

Design Exchange Format (DEF) . is used to represent the physical layout of an IC in an ASCII format. It represents the netlist and circuit layout. We used DEF along with LEF (Library Exchange Format) to represent complete physical layout of an integrated circuit while it is being designed.

What is DRV in VLSI?

DRV(Design Rule Violations) and DRC(Design rule check) are the terms used judge the quality of chip in different stages in VLSI Physical Design. DRC: It is actually used for making sure layout of a design must be in accordance with a set of predefined technology rules given by the foundry for manufacturability.

What is DFT latch?

A lock up latch is a sequential circuit which is used to address skew problems when multiple clock domains are used in a chip. From a DFT perspective it holds the previous scan data, and delays output transition so that the scan data can be effectively captured.

Why lockup latches are used?

Lock-up latches are used in between the two scan flops having large hold failure probability due to uncommon clock path so that there is no issue in closing timing in a scan chain across domains in scan-shift mode.

What is DEF and LEF?

Library Exchange Format (LEF) is a specification for representing the physical layout of an integrated circuit in an ASCII format. LEF is used in conjunction with Design Exchange Format (DEF) to represent the complete physical layout of an integrated circuit while it is being designed.

What is difference between DRC and DRV in VLSI?

The main DRCs include shorts, opens, spacing between metals, n and p wells, same and different nets, min length, area and enclosure etc. DRV: The DRV holds a higher priority to DRC at any given stage of VLSI PD flow. DRV is basically the set of factors based on which the design is characterized.