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. From timing perspective lock-up latches can be the best solution to avoid large uncommon path between the clocks of two flops.
What is lockup latch in DFT?
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.
In which path we insert the lockup latch data or clock path?
The hold check between lockup latch and domain2 flop is already relaxed as it is half cycle check. So, we can say that the correct way to insert a lockup latch is to insert it closer to launching flop and connect the launch domain clock to its clock pin.
Can latches be part of scan chains explain?
Full Member level 2 Can latches be part of scan chains, explain. yes.. if you design is latch based then you can implement the LSSD style scan instead of mux-scan.
What is transparent latch in DFT?
A transparent latch is a storage element. It has an input, an output, and an enable or gate pin. When the enable is active, the output transparently follows the input (with some small delay). Transparent latches are described elsewhere on the website in VHDL and Verilog.
What is clock mixing in DFT?
Majorly, in DFT, we avoid mixing different clocks in the same chain, but if there is a constraint to I/O ports we have to stitch scan flops driven by two different clocks in one chain.
How do you make a latch transparent?
latches are designed to be transparent. by adding enable control signal to latch it can be made non-transparent which mean when enable is active output follows input.
Which is a transparent latch?
A “transparent latch” is one where the inputs are passed straight through to the outputs when the “select” signal is active. When the select signal goes inactive, the final input state is latched on the outputs.
What is scan insertion in DFT?
Scan Insertion: Tool Objective. SCAN is a DFT design technique used in IC Design to increase the overall testability of a circuit. 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.
Why DFT is required?
Chip production: DFT at this stage helps to test the overall shipped-product quality. To ensure the smooth working of the product, chips are thoroughly checked and tested. Board-level test: DFT at this stage helps to test the operational life of chips with a temperature test.
What is the multi clock domain design?
The difference between the single clock domain and multiple clock domain designs is the phase difference between arrivals of the clock signals. The clock sources CLK1 and CLK2 are different for both the domains and regardless of the same or different frequencies the design is treated as multiple clock domain design.
How does a transparent latch work?
A transparent latch is a storage element. It has an input, an output, and an enable or gate pin. When the enable is active, the output transparently follows the input (with some small delay). When the enable becomes inactive, the output freezes.
What is a lock-up Latch?
A lock-up latch is nothing more than a transparent latch used intelligently in the places where clock skew is very large and meeting hold timing is a challenge due to large uncommon clock path.
What is the lock-up latch on the scan path?
Lock-up latches on the scan path act as “break points” across which flops cannot be reordered. Due to lock-up latch on scan path, tool is not able to improve the chain length by reordering in an efficient manner. Whenever there is a lock-up latch in the chain, the scan chain is broken into two smaller segments.
How to add a lock-up Latch to a flip-flop?
Insert the buffers, to add sufficient delay, so that hold timing is finally met. Add the Lock-Up Latch between the two flip-flops where scan chain crosses the functional domains. The first might not be a robust solution because the delay of the buffers would vary across the PVT corners and RC corners.
Why lock-up latches are important for static timing analysis?
This is a guest post by Naman Gupta, a Static Timing Analysis (STA) engineer at a leading semiconductor company in India. Lock-Up Latches are important elements for STA engineer while closing timing on their DFT Modes: particularly the hold timing closure of the Shift Mode.