Understanding CMOS Latch Up Issue in VLSI

CMOS latch-up occurs due to feedback loop sustaining current flow from VDD to ground, causing chip failure.

### Understanding CMOS Latch-Up: The Phenomenon and Modeling
*🔌 CMOS latch-up is a critical issue that occurs within standard cells due to the formation of parasitic elements, leading to a short circuit from VDD to ground.
*📊 The phenomenon is demonstrated through the modeling of NPN and PNP transistors inside CMOS, showing how input or output disturbances can lead to a sustained feedback loop and self-sustained latch-up.
*📏 The naming of "CMOS latch-up" is attributed to the self-sustained feedback loop that can cause a short circuit, persisting even after the removal of the initial disturbances.
*🔍 The video provides a clear explanation of CMOS latch-up and encourages viewers to ask questions, promising more concepts in future videos.

PD Lec 39 - CMOS Latch Up | VLSI | Physical Design

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Understanding CMOS Latch-Up Issue in VLSI Manufacturing

CMOS latch-up issue is a fundamental problem in VLSI manufacturing, involving the formation of parasitic elements inside the chip.

It occurs due to the unintended creation of npn and pnp transistors, leading to unwanted behavior.

The issue is modeled using two transistors to demonstrate its impact on CMOS layout and functionality.

Modeling Transistor Operation with NPN and PNP Transistors

The circuit consists of an NPN transistor connected to the base of a PNP transistor, with the NPN's collector connected to the PNP's base.

The transistors are used for modeling purposes to understand the behavior during operation, such as voltage overshoot.

In the case of overshoot, the terminals of the PMOS and NMOS transistors are connected to the emitter of the PNP transistor, allowing for a better understanding of the impact of overshoot on the circuit.

Understanding the Operation of Transistors

The parasitic elements create a path from VDD to ground, but they are reverse biased to prevent current flow.

If the input or output exceeds VDD, it creates a forward bias, turning on the PMOS and creating a complete path from VDD to ground, potentially causing a power ground short and failure.

If the input or output is less than ground, it can result in the turning on of the parasitic NPN transistor, also leading to potential failure.

Understanding CMOS Latch-Up in Transistors

CMOS latch-up occurs when the input or output voltage exceeds the power supply rails, causing a feedback loop between the NPN and PNP transistors.

This feedback loop allows the latch-up condition to sustain itself independently of the initial voltage disturbances.

The name "latch-up" comes from the self-sustaining nature of this feedback loop, even after the initial disturbances are removed.

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