Latch-Up is a condition where a low impedance path is created between a supply pin and ground. The Latch-Up condition typically requires a power cycle to eliminate the low impedance path. CMOS and BiCMOS circuits use NMOS and PMOS transistors to create the circuit functions.
What causes Latchup?
A common cause of latch-up is a positive or negative voltage spike on an input or output pin of a digital chip that exceeds the rail voltage by more than a diode drop. Another cause is the supply voltage exceeding the absolute maximum rating, often from a transient spike in the power supply.
What is Latchup in VLSI?
Technically latch-up is the phenomena of activating the parasitic BJTs in a CMOS circuit which forms a low impedance path between the power and ground terminals. This low impedance path draws a large current and heats up the IC (Integrated Chip) which cause permanent damage of IC.
What is Latchup in physical design?
A latch-up is a type of short circuit which can occur in an integrated circuit (IC). During a latch-up when one of the transistors is conducting, the other one begins conducting too.
What is latchup in CMOS design and ways to prevent it?
There are several ways to reduce the possibility of latchup:
- Reduce the beta of either or both parasitic devices.
- Increase well and substrate doping concentrations to reduce Rwell and Rsub.
- Provide alternative (or better) collectors of the minority carriers.
What is Latchup in IGBT?
Latch-up results from turning on of the parasitic PNPN thyristor. At that point, the IGBT current is no longer controlled by the. MOS gate. The IGBT would be destroyed unless the current is externally forced OFF.
What are spare cells and why it is used?
Spare cells are basically elements embedded in the design which are not driving anything. The idea is that maybe they will enable an easy (metal) fix without the need of a full redesign.
How do you stop latch in CMOS?
There are several ways to reduce the possibility of latchup: Reduce the beta of either or both parasitic devices. In practice this can be achieved by increasing the spacing between the devices, which increases the width of the lateral device. However, such increased spacing reduces packing density.
What is delay in CMOS?
The propagation delay of a logic gate e.g. inverter is the difference in time (calculated at 50% of input-output transition), when output switches, after application of input. The propagation delay high to low (tpHL) is the delay when output switches from high-to-low, after input switches from low-to-high.
How guard ring prevent latch up?
You will always have the parasitic bjt’s, guard rings try to minimize the chances of turning on these bjts which result in latch up. consider you get a esd current spike, and you sink that current into your nwell, via a protection diode.
What is spare cell?
Spare cells are basically elements embedded in the design which are not driving anything. The idea is that maybe they will enable an easy (metal) fix without the need of a full redesign. Having spare cells might mean that we are able to fix a design for a few 10K dollars (sometimes less) rather than a few 100K.
What is the use of spare cells?
Use of Spare cells: Spare cells enable us to modify/improve the functionality of a chip with minimal changes in the mask. We can use already placed spare cells from the nearby location and just need to modify the metal interconnect. There is no need to make any changes in the base layers.
What is latchup in CMOS?
vlsi universe Latchup and its prevention in CMOS devices What is Latchup : Latchup refers to short circuit formed between power and ground rails in an IC leading to high current and damage to the IC.
What is latch up in CMOS transistors?
Speaking about CMOS transistors, latch up is the phenomenon of low impedance path between power rail and ground rail due to interaction between parasitic pnp and npn transistors. The structure formed by these resembles a Silicon Controlled rectifier (SCR, usually known as a thyristor, a PNPN device used in power electronics).
What is latch up problem in VLSI design?
Latch Up Problem in CMOS – VLSI Design. Latch-up is defined as the generation of a low-impedance path in CMOS chips between the power supply (VDD) and the ground (GND) due to the interaction of parasitic PNP and NPN bipolar junction transistors (BJTs).
What is CMOS technology and how does it work?
Complementary Metal Oxide Semiconductor (CMOS) is the dominant technology for manufacturing today’s integrated circuits (ICs). Among other things, CMOS technology owes its dominance to two key features. Namely, high noise immunity and low power consumption.
